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THE CENTURY SCIENCE SERIES.

Edited by SIR HENRY E. ROSCOE, D.C.L., LL.D., F.R.S.

THE HERSCHELS
AND
MODERN ASTRONOMY

The Century Science Series.

EDITED BY
SIR HENRY E. ROSCOE, D.C.L., F.R.S., M.P.

John Dalton and the Rise of Modern Chemistry.

By Sir Henry E. Roscoe, F.R.S.

Major Rennell, F.R.S., and the Rise of English Geography.

By Clements R. Markham, C.B., F.R.S., President of the Royal Geographical Society.

The Herschels and Modern Astronomy.

By Miss Agnes M. Clerke, Author of “A Popular History of Astronomy during the 19th Century,” &c.

In Preparation.

Justus von Liebig: his Life and Work.

By W. A. Shenstone, Science Master in Clifton College.

Michael Faraday: his Life and Work.

By Professor Silvanus P. Thompson, F.R.S.

Clerk Maxwell and Modern Physics.

By R. T. Glazebrook, F.R.S., Fellow of Trinity College, Cambridge.

Charles Lyell: his Life and Work.

By Rev. Professor T. G. Bonney, F.R.S.

Humphry Davy.

By T. E. Thorpe, F.R.S., Principal Chemist of the Government Laboratories.

Pasteur: his Life and Work.

By Armand Ruffer, Director of the British Institute of Preventive Medicine.

Charles Darwin and the Origin of Species.

By Edward B. Poulton, M.A., F.R.S., Hope Professor of Zoology in the University of Oxford.

Hermann von Helmholtz.

By A. W. Rücker, F.R.S., Professor of Physics in the Royal College of Science, London.

CASSELL & COMPANY, Limited, London; Paris & Melbourne.

SIR WILLIAM HERSCHEL.

Ætat. 50.

(From Abbott’s painting in the National Portrait Gallery.)

THE CENTURY SCIENCE SERIES.

The Herschels
AND
MODERN ASTRONOMY

BY
AGNES M. CLERKE

AUTHOR OF
“A POPULAR HISTORY OF ASTRONOMY DURING THE 19TH CENTURY,”
“THE SYSTEM OF THE STARS,” ETC.

CASSELL and COMPANY, Limited
LONDON, PARIS & MELBOURNE
1895

ALL RIGHTS RESERVED

PREFACE.

The chief authority for the Life of Sir William Herschel is Mrs. John Herschel’s “Memoir of Caroline Herschel” (London, 1876). It embodies Caroline’s Journals and Recollections, the accuracy of which is above suspicion. William himself, indeed, referred to her for dates connected with his early life. The collateral sources of information are few and meagre; they yield mere gleanings, yet gleanings worth collecting. Professor E. S. Holden has had recourse to many of them for his excellent little monograph entitled “Herschel, his Life and Works” (London, 1881), which is usefully supplemented by “A Synopsis of the Scientific Writings of Sir William Herschel,” prepared by the same author with the aid of Professor Hastings. It made part of the Smithsonian Report for 1880, and was printed separately at Washington in 1881. But the wonderful series of papers it summarises have still to be sought, one by one, by those desiring to study them effectually, in the various volumes of the Philosophical Transactions in which they originally appeared. Their collection and republication is, nevertheless, a recognised desideratum, and would fill a conspicuous gap in scientific literature.

Sir John Herschel’s life has yet to be written. The published materials for it are scanty, although they have been reinforced by the inclusion in the late Mr. Graves’s “Life of Sir William Rowan Hamilton” (Dublin, 1882–9) of his correspondence with that remarkable man. The present writer has, however, been favoured by the late Miss Herschel, and by Sir William J. Herschel, with the perusal of a considerable number of Sir John Herschel’s, as well as of Sir William’s, manuscript letters. She also gratefully acknowledges the kind help afforded to her by Lady Gordon and Miss Herschel in connection with the portraits reproduced in this volume. For detailed bibliographical references, the articles on Sir John, Sir William, and Caroline Herschel, in the “Dictionary of National Biography,” may be consulted.

CONTENTS.

ILLUSTRATIONS.

The Herschels
AND
MODERN ASTRONOMY.

CHAPTER I.
EARLY LIFE OF WILLIAM HERSCHEL.

William Herschel was descended from one of three brothers, whose Lutheran opinions made it expedient for them to quit Moravia early in the seventeenth century. Hans Herschel thereupon settled as a brewer at Pirna, in Saxony; his son Abraham rose to some repute as a landscape-gardener in the royal service at Dresden; and Abraham’s youngest son, Isaac, brought into the world with him, in 1707, an irresistible instinct and aptitude for music. Having studied at Berlin, he made his way in 1731 to Hanover, where he was immediately appointed oboist in the band of the Hanoverian Guard. A year later he married Anna Ilse Moritzen, by whom he had ten children. The fourth of these, Frederick William, known to fame as William Herschel, was born November 15th, 1738.

His brilliant faculties quickly displayed themselves. At the garrison-school he easily distanced his brother Jacob, his senior by four years, and learned besides, privately, whatever French and mathematics the master could teach him. He showed also a pronounced talent for music, and was already, at fourteen, a proficient on the hautboy and violin. In this direction lay his manifest destiny. His father was now bandmaster of the Guard; he was poor, and had no other provision to give his sons than to train them in his own art; and thus William, driven by necessity to become self-supporting while still a boy, entered the band as oboist in 1753. They were a family of musicians. Of the six who reached maturity, only Mrs. Griesbach, the elder daughter, gave no sign of personally owning a share in the common gift, which descended, nevertheless, to her five sons, all noted performers on sundry instruments.

William Herschel accompanied his regiment to England in 1755, with his father and elder brother. He returned a year later, bringing with him a copy of Locke “On the Human Understanding,” upon which he had spent the whole of his small savings. Two of the three volumes thus acquired were recovered by his sister after seventy years, and transmitted to his son. The breaking-out of the Seven Years’ War proved decisive as to his future life. Campaigning hardships visibly told upon his health; his parents resolved, at all hazards, to rescue him from them; and accordingly, after the disaster at Hastenbeck, July 26th, 1757, they surreptitiously shipped him off to England. By this adventure, since he was in the military service of the Elector of Hanover, George III. of England, he incurred the penalties of desertion; but they were never exacted, and were remitted by the King himself in 1782.

William Herschel was in his nineteenth year when he landed at Dover with a French crown-piece in his pocket. Necessity or prudence kept him for some time obscure; and we next hear of him as having played a solo on the violin at one of Barbandt’s concerts in London, February 15th, 1760. In the same year he was engaged by the Earl of Darlington to train the band of the Durham Militia, when his shining qualities brought him to the front. The officers of the regiment looked with astonishment on the phenomenal young German who had dropped among them from some cloudy region; who spoke English perfectly, played like a virtuoso, and possessed a curious stock of varied knowledge. Their account of him at a mess-dinner excited the curiosity of Dr. Miller, organist and historian of Doncaster, who, having heard him perform a violin solo by Giardini, fell into a rapture, and invited him on the spot to live with him.

He left nothing undone for the advancement of his protégé; procured for him tuitions and leading concert engagements; and encouraged him, in 1765, to compete for the post of organist at Halifax. Herschel’s special qualifications were small; his chief rival, Dr. Wainwright, was a skilled player, and at the trial performance evoked much applause by his brilliant execution. Only the builder of the organ, an odd old German named Schnetzler, showed dissatisfaction, exclaiming: “He run about the keys like one cat; he gif my pipes no time for to shpeak.” Then Herschel mounted the loft, and the church was filled with a majestic volume of sound, under cover of which a stately melody made itself heard. The “Old Hundredth” followed, with equal effect. Schnetzler was beside himself with delight. “I vil luf dis man,” he cried, “because he git my pipes time for to shpeak.” Herschel had virtually provided himself with four hands. A pair of leaden weights brought in his pocket served to keep down two keys an octave apart, while he improvised a slow air to suit the continuous bass thus mechanically supplied. The artifice secured him the victory.

This anecdote is certainly authentic. It is related by Dr. Miller from personal knowledge. Nor is it inconsistent with a story told by Joah Bates, of King’s College, Cambridge, a passionate lover of music. Repairing to Halifax, his native place, to conduct the “Messiah” at the opening of a new organ, he was accosted in the church by a young man, who asked for an opportunity of practising on it. Although as yet, he said, unacquainted with the instrument, he aspired to the place of organist; and the absolute certitude of his manner so impressed Bates that he not only granted his request, but became his warm patron. The young man’s name was William Herschel. We hear, further, on Dr. Burney’s authority, that he played first violin in Bates’s orchestra.

But the tide of his fortunes was flowing, and he knew how to “take it at the flood.” Early in 1766 he removed to Bath as oboist in Linley’s celebrated orchestra, which played daily in the Pump Room to enliven the parade of blushing damsels and ruffling gallants pictured to our fancy in Miss Austen’s novels. Bath was then what Beau Nash had made it—the very focus of polite society. Turbans nodded over cards; gigs threaded their way along Union Passage; Cheap Street was blocked with vehicles; the Lower Rooms witnessed the nightly evolutions of the country-dance; the Grove, as Doran reminds us, was brilliant with beauty, coquelicot ribbons, smart pelisses, laced coats, and ninepins. The feat of “tipping all nine for a guinea” was frequently performed; and further excitement might be had by merely plucking some lampoons from the trees, which seemed to bear them as their natural fruit. Music, too, was in high vogue. The theatres were thronged; and Miss Linley’s exquisite voice was still heard in the concert-halls.

On the 4th of October, 1767, the new Octagon Chapel was opened for service, with Herschel as organist. How it was that he obtained this “agreeable and lucrative situation” we are ignorant; but he had that singular capacity for distinction which explains everything. The Octagon Chapel became a centre of fashionable attraction, and he soon found himself lifted on the wave of public favour. Pupils of high rank thronged to him, and his lessons often mounted to thirty-five a week. He composed anthems, psalm-tunes, even full services for his assiduously-trained choir. His family were made sharers in his success. He secured a post in Linley’s orchestra for his younger brother Alexander, in 1771; and he himself fetched his sister Caroline to Bath in 1772. Both were of very considerable help to him in his musical and other enterprises, the latter of which gradually gained ground over the former.

Music was never everything to William Herschel. He cultivated it with ardour; composed with facility in the prevalent graceful Italian style; possessed a keen appreciation and perfect taste. But a musical career, however brilliant, did not satisfy him. The inner promptings of genius told him to look beyond. The first thirty-five years of his life were thus spent in diligently preparing to respond to an undeclared vocation. Nothing diverted him from his purpose of self-improvement. At first, he aimed chiefly at mastering the knowledge connected with his profession. With a view to the theory of music, “I applied myself early,” he said, in a slight autobiographical sketch sent to Lichtenberg at Göttingen, “to all the branches of the mathematics, algebra, conic sections, fluxions, etc. Contracting thereby an insatiable desire for knowledge in general, I extended my application to languages—French, Italian, Latin, English—and determined to devote myself entirely to the pursuit of knowledge, in which I resolved to place all my future enjoyment and felicity. This resolution I have never had occasion to change.” At Bath, in the midst of engrossing musical occupations, his zeal for study grew only the more intense. After fourteen or sixteen hours of teaching, he would “unbend his mind” by plunging into Maclaurin’s “Fluxions,” or retire to rest with a basin of milk, Smith’s “Opticks,” and Ferguson’s “Astronomy.” He had no sooner fallen under the spell of this last science than he “resolved to take nothing upon trust, but to see with my own eyes all that other men had seen before.”

He hired, to begin with, a small reflector; but what it showed him merely whetted his curiosity. And the price of a considerably larger instrument proved to be more than he could afford to pay. Whereupon he took the momentous resolution of being, for the future, his own optician. This was in 1772. He at first tried fitting lenses into pasteboard tubes, with the poor results that can be imagined. Then he bought from a Quaker, who had dabbled in that line, the discarded rubbish of his tools, patterns, polishers, and abortive mirrors; and in June, 1773, when fine folk had mostly deserted Bath for summer resorts, work was begun in earnest. The house was turned topsy-turvy; the two brothers attacked the novel enterprise with boyish glee. Alexander, a born mechanician, set up a huge lathe in one of the bedrooms; a cabinet-maker was installed in the drawing-room; Caroline, in spite of secret dismay at such unruly proceedings, lent a hand, and kept meals going; William directed, inspired, toiled, with the ardour of a man who had staked his life on the issue. Meanwhile, music could not be neglected. Practising and choir-training went on; novelties for the ensuing season were prepared; compositions written, and parts copied. Then the winter brought the usual round of tuitions and performances, while all the time mirrors were being ground and polished, tried and rejected, without intermission. At last, after two hundred failures, a tolerable reflecting telescope was produced, about five inches in aperture, and of five and a half feet focal length. The outcome may seem small for so great an expenditure of pains; but those two hundred failures made the Octagon Chapel organist an expert, unapproached and unapproachable, in the construction of specula. With his new instrument, on March 4th, 1774, he observed the Nebula in Orion; and a record of this beginning of his astronomical work is still preserved by the Royal Society.

William Herschel was now, as to age, in mezzo cammin. He had numbered just so many years as had Dante when he began the “Divina Commedia.” But he had not, like Dante, been thrown off the rails of life. The rush of a successful professional career was irresistibly carrying him along. Almost any other man would have had all his faculties absorbed in it. Herschel’s were only stimulated by the occupations which it brought. Yet they were of a peculiarly absorbing nature. Music is the most exclusive of arts. In turning aside, after half a lifetime spent in its cultivation, to seek his ideal elsewhere, Herschel took an unparalleled course. And his choice was final. Music was long his pursuit, astronomy his pastime; a fortunate event enabled him to make astronomy his pursuit, while keeping music for a pastime.

Yet each demands a totally different kind of training, not only of the intellect, but of the senses. From his earliest childhood William Herschel’s nerves and brain had been specially educated to discriminate impressions of sound, and his muscles to the peculiar agility needed for their regulated and delicate production; while, up to the age of thirty-five, he had used his eyes no more purposefully than other people. The eye, nevertheless, requires cultivation as much as the ear. “You must not expect to see at sight,” he told Alexander Aubert, of Loam Pit Hill, in 1782. And he wrote to Sir William Watson: “Seeing is in some respects an art which must be learnt. Many a night have I been practising to see, and it would be strange if one did not acquire a certain dexterity by such constant practice.” A critical observation, he added, could no more be expected from a novice at the telescope than a performance of one of Handel’s organ-fugues from a beginner in music. In this difficult art of vision he rapidly became an adept. Taking into account the full extent of his powers, the opinion has been expressed, and can scarcely be contradicted, that he never had an equal.

At midsummer, 1774, Herschel removed from No. 7, New King Street, to a house situated near Walcot Turnpike, Bath. A grass-plot was attached to the new residence, and it afforded convenient space for workshops. For already he designed to “carry improvements in telescopes to their utmost extent,” and “to leave no spot of the heavens unvisited.” An unprecedented ambition! No son of Adam had ever before entertained the like. To search into the recesses of space, to sound its depths, to dredge up from them their shining contents, to classify these, to investigate their nature, and trace their mutual relations, was what he proposed to do, having first provided the requisite optical means. All this in the intervals of professional toils, with no resources except those supplied by his genius and ardour, with no experience beyond that painfully gained during the progress of his gigantic task.

Since the time of Huygens, no systematic attempt had been made to add to the power of the telescope. For the study of the planetary surfaces, upon which he and his contemporaries were mainly intent, such addition was highly desirable. But Newton’s discovery profoundly modified the aims of astronomers. Their essential business then became that of perfecting the theories of the heavenly bodies. Whether or not they moved in perfect accordance with the law of gravitation was the crucial question of the time. Newton’s generalisation was on its trial. Now and again it almost seemed as if about to fail. But difficulties arose only to be overcome, and before the eighteenth century closed the superb mechanism of the planetary system was elucidated. Working flexibly under the control of a single dominant force, it was shown to possess a self-righting power which secured its indefinite duration. Imperishable as the temple of Poseidon, it might be swayed by disturbances, but could not be overthrown.

The two fundamental conclusions—that the Newtonian law is universally valid, and that the solar system is a stable structure—were reached by immense and sustained labours. Their establishment was due, in the main, to the mathematical genius of Clairaut, D’Alembert, Lagrange, and Laplace. But refined analysis demands refined data; hence the need for increased accuracy of observation grew continually more urgent. Attention was accordingly concentrated upon measuring, with the utmost exactitude, the places at determinate epochs of the heavenly bodies. The one thing needful was to learn the “when” and “where” of each of them—that is, to obtain such information as the transit-instrument is adapted to give. In this way the deviations of the moon and planets from their calculated courses became known; and upon the basis of these “errors” improved theories were built, then again compared with corrected observations.

For these ends, large telescopes would have been useless. They were not, however, those that Herschel had in view. The nature of the orbs around us, not their motions, formed the subject of his inquiries, with which modern descriptive astronomy virtually originated. He was, moreover, the founder of sidereal astronomy. The stars had, until his career began, received little primary attention. They were regarded and observed simply as reference-points by which to track the movements of planets, comets, and the moon. Indispensable for fiducial purposes, they almost escaped consideration for themselves. They were, indeed, thought to lie beyond the reach of effective investigation. Only the outbursts of temporary stars, and the fluctuations of two or three periodical ones, had roused special interest, and seemed deserving of particular inquiry.

Of the dim objects called “nebulæ,” Halley had counted up half a dozen in 1714; Lacaille compiled a list of forty-two at the Cape, in 1752–55; and Messier published at Paris, in 1771, a catalogue of forty-five, enlarged to one hundred and three in 1781. He tabulated, only to rid himself of embarrassments from them. For he was by trade a comet-hunter, and, until he hit upon this expedient, had been much harassed in its exercise by mistakes of identity.

But Herschel did not merely “pick up;” he explored. This was what no one before him had thought of doing. A “review of the heavens” was a complete novelty. The magnificence of the idea, which was rooted in his mind from the start, places him apart from, and above, all preceding observers.

To its effective execution telescopic development was essential. The two projects of optical improvement and of sidereal scrutiny went together. The skies could be fathomed, if at all, only by means of light-collecting engines of unexampled power. Rays enfeebled by distance should be rendered effective by concentration. Stratum after stratum of bodies—

“Clusters and beds of worlds, and bee-like swarms

Of suns and starry streams,”

previously unseen, and even unsuspected, might, by the strong focussing of their feebly-surviving rays, be brought to human cognisance. The contemplated “reviews” would then be complete just in proportion to the grasp of the instrument used in making them.

The first was scarcely more than a reconnaissance. It was made in 1775, with a small reflector of the Newtonian make.[A] Its upshot was to impress him with the utter disproportion between his daring plans and the means as yet at his disposal. Speculum-casting accordingly recommenced with fresh vigour. Seven- and ten-foot mirrors were succeeded by others of twelve, and even of twenty feet focal length. The finishing of them was very laborious. It was at that time a manual process, during the course of which the hands could not be removed from the metal without injury to its figure. One stretch of such work lasted sixteen hours, Miss Herschel meantime, “by way of keeping him alive,” putting occasional morsels of food into the diligent polisher’s mouth. His mode of procedure was to cast and finish many mirrors of each sort; then to select the best by trial, and repolish the remainder. In this manner he made, before 1781, “not less than 200 seven-foot, 150 ten-foot, and about 80 twenty-foot mirrors, not to mention those of the Gregorian form.” Repolishing operations were, moreover, accompanied by constant improvements, so that each successive speculum tended to surpass its predecessors.

[A] In “Newtonian” telescopes the image formed by the large speculum is obliquely reflected from a small plane mirror to the side of the tube, where it is viewed with an ordinary eye-piece. With a “Gregorian,” the observer looks straight forward, the image being thrown back by a little concave mirror through a central perforation in the speculum where the eye-piece is fitted.

These absorbing occupations were interrupted by the unwelcome news that Dietrich, the youngest of the Herschel family, had decamped from Hanover “with a young idler” like himself. William instantly started for Holland, where the fugitive was supposed to be about to take ship for India, but missed his track; and, after having extended his journey to Hanover to comfort his anxious mother—his father had died in 1767—returned sadly to Bath. There, to his immense surprise, he found the scapegrace in strict charge of his sister, “who kept him to a diet of roasted apples and barley-water.” His ineffectual escapade had terminated with an attack of illness at Wapping, whither Alexander Herschel, on learning how matters stood, had posted off to take him in charge and watch his recovery. Musical occupation was easily procured for him at Bath, since he was an accomplished violinist—had, indeed, started on his unprosperous career in the guise of an infant prodigy; but he threw it up in 1779 and drifted back to Hanover, married a Miss Reif, and settled down to live out a fairly long term of shiftless, albeit harmless, existence.

In 1776 William Herschel succeeded Thomas Linley, Sheridan’s father-in-law, as Director of the Public Concerts at Bath. His duties in this capacity, while the season lasted, were most onerous. He had to engage performers, to appease discontents, to supply casual failures, to write glees and catches expressly adapted to the voices of his executants, frequently to come forward himself as a soloist on the hautboy or the harpsichord. The services of his brother Alexander, a renowned violoncellist, and of his sister, by this time an excellent singer, were now invaluable to him. Nor for musical purposes solely. The vision of the skies was never lost sight of, and the struggle to realise it in conjunction with his sympathetic helpers absorbed every remnant of time. At meals the only topics of conversation were mechanical devices for improving success and averting failure. William ate with a pencil in his hand, and a project in his head. Between the acts at the theatre, he might be seen running from the harpsichord to his telescope. After a rehearsal or a morning performance, he would dash off to the workshop in periwig and lace ruffles, and leave it but too often with those delicate adjuncts to his attire torn and pitch-bespattered. Accidents, too, menacing life and limb, were a consequence of that “uncommon precipitancy which accompanied all his actions;” but he escaped intact, save for the loss of a finger-nail.

His introduction to the learned world of Bath was thus described by himself:—

“About the latter end of December, 1779, I happened to be engaged in a series of observations on the lunar mountains; and the moon being in front of my house, late in the evening I brought my seven-feet reflector into the street, and directed it to the object of my observations. Whilst I was looking into the telescope, a gentleman, coming by the place where I was stationed, stopped to look at the instrument. When I took my eye off the telescope, he very politely asked if he might be permitted to look in, and this being immediately conceded, he expressed great satisfaction at the view.”

The inquisitive stranger called next morning, and proved to be Dr. (later Sir William) Watson. He formed on the spot an unalterable friendship for the moon-struck musician, and introduced him to a Philosophical Society which held its meetings at his father’s house. Herschel’s earliest essays were read before it, but they remained unpublished. His first printed composition appeared in the “Ladies’ Diary” for 1780. It was an answer to a prize question on the vibration of strings.

The long series of his communications to the Royal Society of London opened May 11th, 1780, with a discussion of his observations, begun in October, 1777, of Mira, the variable star in the neck of the Whale. As to the theory of its changes, he agreed with Keill that they could best be explained by supposing rotation on an axis to bring a lucid side and a side obscured by spots alternately into view. A second paper by him on the Mountains of the Moon was read on the same day. He measured, in all, about one hundred of these peaks and craters.

In January, 1781, there came an essay stamped with the peculiar impress of his genius, entitled “Astronomical Observations on the Rotation of the Planets round their Axes, made with a view to determine whether the earth’s diurnal motion is perfectly equable.” It embodied an attempt to apply a definite criterion to the time-keeping of our planet. But the prospect is exceedingly remote of rating one planet-clock by the other. Herschel’s methods of inquiry are, however, aptly illustrated in this curiously original paper. His speculations always invited the control of facts. If facts were not at hand, he tried somehow to collect them. The untrammelled play of fancy was no more to his mind than it was to Newton’s. His ardent scientific imagination was thus, by the sobriety of his reason, effectively enlisted in the cause of progress.

Herschel began in 1780 his second review of the heavens, using a seven-foot Newtonian, of 6¼ inches aperture, with a magnifying power of 227. “For distinctness of vision,” he said, “this instrument is, perhaps, equal to any that was ever made.” His praise was amply justified. As he worked his way with it through the constellation Gemini, on the night of March 13th, 1781, an unprecedented event occurred. “A new planet swam into his ken.” He did not recognise it as such. He could only be certain that it was not a fixed star. His keen eye, armed with a perfect telescope, discerned at once that the object had a disc; and the application of higher powers showed the disc to be a substantial reality. The stellar “patines of bright gold” will not stand this test. Being of purely optical production, they gain nothing by magnification.

At that epoch new planets had not yet begun to be found by the dozen. Five, besides the earth, had been known from the remotest antiquity. Five, and no more, seemed to have a prescriptive right to exist. The boundaries of the solar system were of immemorial establishment. It was scarcely conceivable that they should need to be enlarged. The notion did not occur to Herschel. His discovery was modestly imparted to the Royal Society as “An Account of a Comet.” He had, indeed, noticed that the supposed comet moved in planetary fashion from west to east, and very near the ecliptic; and, after a few months, its true nature was virtually proved by Lexell of St. Petersburg. On November 28th, Herschel measured, with his freshly-invented “lamp-micrometer,” the diameter of this “singular star;” and it was not until a year later, November 7th, 1782, that he felt sufficiently sure of its planetary status to exercise his right of giving it a name. Yet this, in the long run, he failed to accomplish. The appellation “Georgium Sidus,” bestowed in honour of his patron, George III., never crossed the Channel, and has long since gone out of fashion amongst ourselves. Lalande tried to get the new planet called “Herschel;” but the title “Uranus,” proposed by Bode, of Berlin, was the “fittest,” and survived.

This discovery made the turning-point of Herschel’s career. It transformed him from a music-master into an astronomer. Without it his vast abilities would probably have been in great measure wasted. No man could long have borne the strain of so arduous a double life as he was then leading. Relief from it came just in time. It is true that fame, being often more of a hindrance than a help, brought embarrassments in its train. In November, 1781, Herschel was compelled to break the complex web of his engagements at Bath by a journey to London for the purpose of receiving in person the Copley Medal awarded to him by the Royal Society, of which body he was, some days later, elected a Fellow. At home, he was persecuted by admirers; and they were invariably received with an easy suavity of manner that gave no hint of preoccupation. Everyone of scientific pretension who visited Bath sought an interview with the extraordinary man who, by way of interlude to pressing duties, had built telescopes of unheard-of power, and performed the startling feat of adding a primary member to the solar system. Among the few of these callers whose names have been preserved were Sir Harry Englefield, Sir Charles Blagden, and Dr. Maskelyne, then, and for thirty years afterwards, Astronomer-Royal. “With the latter,” Miss Herschel relates, “he (William) was engaged in a long conversation which to me sounded like quarrelling, and the first words my brother said after he was gone were, ‘That is a devil of a fellow!’” The phrase was doubtless meant as a sign of regard, for the acquaintance thus begun ripened into cordial intimacy. And William Herschel never lost or forgot a friend.

As regards music alone, the winter of 1781–82 was an exceptionally busy one. He had arranged to conduct, jointly with Rauzzini, a Roman singer and composer, a series of oratorios; undertaking, besides, pecuniary responsibilities which turned out little to his advantage. The labour, vexation, and disappointment involved in carrying out this unlucky plan can readily be imagined. But neither the pressure of business, nor the distractions of celebrity, checked the ardour of his scientific advance. The review which afforded him the discovery of Uranus, and the materials for his first catalogue of 269 double stars, was completed in 1781; and a third, made with the same beautiful instrument, bearing the high magnifying power of 460, was promptly begun. This had for one of its special objects the ascertainment of possible changes in the heavens since Flamsteed’s time; and in the course of it many thousands of stars came under scrutiny, directed to ascertain their magnitude and colour, singleness or duplicity, hazy or defined aspect.

The first of Herschel’s effective twenty-foot telescopes was erected at 19, New King Street, in the summer of 1781. Enclosing a mirror twelve inches in diameter, it far surpassed any seeing-machine that had ever existed in the world. Yet its maker regarded it as only marking a step in his upward progress. A speculum of thirty-feet focus was the next object of his ambition. For its achievement no amount of exertion was counted too great. Its composition was regulated by fresh experiments on various alloys of copper and tin. Its weight and shape were again and again calculated, and the methods appropriate to its production earnestly discussed. “I saw nothing else,” Caroline Herschel tells us, “and heard nothing else talked of but these things when my brothers were together.”[B]

[B] In borrowing Miss Herschel’s lively narratives and comments, some obvious slips in grammar and construction have been corrected. Quotations, too, from the writings of Sir William and Sir John Herschel are often slightly abridged.

“The mirror,” she continues, “was to be cast in a mould of loam prepared from horse-dung, of which an immense quantity was to be pounded in a mortar and sifted through a fine sieve. It was an endless piece of work, and served me for many an hour’s exercise; and Alex frequently took his turn at it, for we were all eager to do something towards the great undertaking. Even Sir William Watson would sometimes take the pestle from me when he found me in the work-room.”

The matter was never out of the master’s thoughts. “If a minute could but be spared in going from one scholar to another, or giving one the slip, he called at home to see how the men went on with the furnace, which was built in a room below, even with the garden.”

At last, the concert season being over, and everything in readiness for the operation of casting, “the metal,” we hear from the same deeply-interested eyewitness, “was in the furnace; but, unfortunately, it began to leak at the moment when ready for pouring, and both my brothers, and the caster with his men, were obliged to run out at opposite doors, for the stone flooring, which ought to have been taken up, flew about in all directions, as high as the ceiling. My poor brother William fell, exhausted with heat and exertion, on a heap of brickbats. Before the second casting was attempted, everything which could ensure success had been attended to, and a very perfect metal was found in the mould, which had cracked in the cooling.”

This second failure terminated the enterprise. Not that it was abandoned as hopeless, but because of a total change in the current of affairs. Herschel’s fame had stirred the royal curiosity, and rumours had now and again reached Bath that he was to be sent for to court. In the spring of 1782 the actual mandate arrived; and on May 8th, leaving his pupils and his projects to shift for themselves, he set out for London. He carried with him his favourite seven-foot reflector, and all the apparatus necessary for viewing double stars and other objects of interest. On May 25th he wrote to his sister:—

“I have had an audience of His Majesty this morning, and met with a very gracious reception. I presented him with the drawing of the solar system, and had the honour of explaining it to him and the Queen. My telescope is in three weeks’ time to go to Richmond, and meanwhile to be put up at Greenwich.... Tell Alexander that everything looks very like as if I were to stay here. The King enquired after him, and after my great speculum. He also gave me leave to come and hear the Griesbachs (Herschel’s nephews) play at the private concert which he has every evening.... All my papers are printing, and are allowed to be very valuable. You see, Lina, I tell you all these things. You know vanity is not my foible, therefore I need not fear your censure. Farewell.”

His next letter is dated June 3rd, 1782. “I pass my time,” he informed “Lina,” “between Greenwich and London agreeably enough, but am rather at a loss for work that I like. Company is not always pleasing, and I would much rather be polishing a speculum. Last Friday I was at the King’s concert to hear George play. The King spoke to me as soon as he saw me, and kept me in conversation for half an hour. He asked George to play a solo-concerto on purpose that I might hear him.... I am introduced to the best company. To-morrow I dine at Lord Palmerston’s, next day with Sir Joseph Banks, etc. Among opticians and astronomers nothing now is talked of but what they call my great discoveries. Alas! this shows how far they are behind, when such trifles as I have seen and done are called great. Let me but get at it again! I will make such telescopes and see such things—that is, I will endeavour to do so.”

A comparison of his telescope with those at the Royal Observatory showed its striking superiority, although among them was one of Short’s famous Gregorians, of 9½ inches aperture. It had thus a reflecting surface above twice that of Herschel’s seven-foot, the competition with which was nevertheless so disastrous to its reputation that Dr. Maskelyne fell quite out of conceit with it, and doubted whether it deserved the new stand constructed for it on the model of Herschel’s.

In the midst of these scientific particulars, we hear incidentally that influenza was then so rife in London that “hardly one single person” escaped an attack.

On July 2nd he made his first appearance as showman of the heavens to royalty. The scene of the display was Buckingham House (now Buckingham Palace). “It was a very fine evening,” he wrote to his sister. “My instrument gave general satisfaction. The King has very good eyes, and enjoys observations with telescopes exceedingly.”

Next night, the King and Queen being absent at Kew, the Princesses desired an exhibition. But, since they objected to damp grass, the telescope, Herschel says, “was moved into the Queen’s apartments, and we waited some time in hopes of seeing Jupiter or Saturn. Meanwhile I showed the Princesses and several other ladies the speculum, the micrometers, the movements of the telescope, and other things that seemed to excite their curiosity. When the evening appeared to be totally unpromising, I proposed an artificial Saturn as an object, since we could not have the real one. I had beforehand prepared this little piece, as I guessed by the appearance of the weather in the afternoon we should have no stars to look at. This being accepted with great pleasure, I had the lamps lighted up, which illuminated the picture of a Saturn (cut out in pasteboard) at the bottom of the garden wall. The effect was fine, and so natural that the best astronomer might have been deceived. Their royal highnesses seemed to be much pleased with the artifice.” From a somewhat prolonged conversation, he judged them to be “extremely well instructed,” and “most amiable characters.”

Shortly afterwards Herschel received the appointment of royal astronomer, with the modest salary of £200 a year. “Never,” exclaimed Sir William Watson on being made acquainted with its amount, “bought monarch honour so cheap!” The provision was assuredly not munificent; yet it sufficed to rescue a great man from submergence under the hard necessities of existence. The offer was critically timed. It was made precisely when teaching and concert-giving had come to appear an “intolerable waste of time” to one fired with a visionary passion. “Stout Cortes” staring at the Pacific, Ulysses starting from Ithaca to “sail beyond the sunset,” were not more eager for experience of the Unknown.

CHAPTER II.
THE KING’S ASTRONOMER.

William Herschel was now an appendage to the court of George III. He had to live near Windsor, and a large dilapidated house on Datchet Common was secured as likely to meet his unusual requirements. The “flitting” took place August 1, 1782. William was in the highest spirits. There were stables available for workrooms and furnaces; a spacious laundry that could be turned into a library; a fine lawn for the accommodation of the great reflector. Crumbling walls and holes in the roof gave him little or no concern; and if butcher’s meat was appallingly dear (as his sister lamented) the family could live on bacon and eggs! In this sunny spirit he entered upon the career of untold possibilities that lay before him.

Nevertheless the King’s astronomer did not find it all plain sailing. His primary duty was to gratify the royal taste for astronomy, and this involved no trifling expenditure of time and toil. The transport of the seven-foot to the Queen’s lodge could be managed in the daylight, but its return-journey in the dark, after the conclusion of the celestial raree-show, was an expensive and a risky business; yet fetched back it should be unless a clear night were to be wasted—a thing not possible to contemplate. This kind of attendance was, however, considerately dispensed with when its troublesome nature came to be fully understood. Herschel’s treatment by George III. has often been condemned as selfish and niggardly; but with scant justice. In some respects, no doubt, it might advantageously have been modified. Still, the fact remains that the astronomer of Slough was the gift to science of the poor mad King. From no other crowned head has it ever received so incomparable an endowment.

Herschel’s salary was undeniably small. It gave him the means of living, but not of observing, as he proposed to observe. If the improvement of telescopes were to be “carried to its utmost limit,” additional funds must be raised. Without an ample supply of the “sinews of war,” fresh campaigns of exploration were out of the question. There was one obvious way in which they could be provided. Herschel’s fame as an optician was spread throughout Europe. His telescopes were wanted everywhere, but could be had from himself alone; for the methods by which he wrought specula to a perfect figure are even now undivulged. They constituted, therefore, a source of profit upon which he could draw to almost any extent. He applied himself, accordingly, to make telescopes for sale. They brought in large sums. Six hundred guineas a-piece were paid to him by the King for four ten-foot reflectors; he received at a later date £3,150 for a twenty-five foot, sent to Spain; and in 1814 £2,310 from Lucien Bonaparte for two smaller instruments. The regular scale of prices (later considerably reduced) began with 200 guineas for a seven-foot, and mounted to 2,500 for a twenty-foot; and the commissions executed were innumerable.

But Herschel did not come into the world to drive a lucrative trade. It was undertaken, not for itself, but for what was to come of it; yet there was danger lest the end should be indefinitely postponed in the endeavour to secure the means.

“It seemed to be supposed,” Miss Herschel remarked, “that enough had been done when my brother was enabled to leave his profession that he might have time to make and sell telescopes. But all this was only retarding the work of a thirty or forty-foot instrument, which it was his chief object to obtain as soon as possible; for he was then on the wrong side of forty-five, and felt how great an injustice he would be doing to himself and the cause of astronomy by giving up his time to making telescopes for other observers.”

This he was, fortunately, not long obliged to do. A royal grant of £2,000 for the construction of the designed giant telescope, followed by another of equal amount, together with an annual allowance of £200 for its repairs, removed the last obstacle to his success. The wide distribution of first-class instruments might, indeed, have been thought to promise more for the advancement of astronomy than the labours of a single individual. No mistake could be greater. Not an observation worth mentioning was made with any of the numerous instruments sent out from Datchet or Slough, save only those acquired by Schröter and Pond. The rest either rusted idly, or were employed ineffectually, aptly illustrating the saying that “the man at the eye-end” is the truly essential part of a telescope.

No one knew this better than Herschel. Every serene dark night was to him a precious opportunity availed of to the last minute. The thermometer might descend below zero, ink might freeze, mirrors might crack; but, provided the stars shone, he and his sister worked on from dusk to dawn. In this way, his “third review,” begun at Bath, was finished in the spring of 1783. The swiftness with which it was conducted implied no want of thoroughness. “Many a night,” he states, “in the course of eleven or twelve hours of observation, I have carefully and singly examined not less than 400 celestial objects, besides taking measures, and sometimes viewing a particular star for half an hour together, with all the various powers.”

The assiduity appears well-nigh incredible with which he gathered in an abundant harvest of nebulæ and double stars; his elaborate papers, brimful of invention and experience, being written by day, or during nights unpropitious for star-gazing. On one occasion he is said to have worked without intermission at the telescope and the desk for seventy-two hours, and then slept unbrokenly for twenty-six hours. His instruments were never allowed to remain disabled. They were kept, like himself, on the alert. Relays of specula were provided, and one was in no case removed from the tube for re-polishing, unless another was ready to take its place. Even the meetings of the Royal Society were attended only when moonlight effaced the delicate objects of his particular search.

The summer of 1788 was spent in getting ready the finest telescope Herschel had yet employed. It was called the “large twenty-foot” because of the size of its speculum, which was nearly nineteen inches in diameter; and with its potent help he executed his fourth and last celestial survey. His impatience to begin led him into perilous situations.

“My brother,” says Miss Herschel, “began his series of sweeps when the instrument was yet in a very unfinished state; and my feelings were not very comfortable when every moment I was alarmed by a crack or fall, knowing him to be elevated fifteen feet or more on a temporary cross-beam instead of a safe gallery. The ladders had not even their braces at the bottom; and one night, in a very high wind, he had hardly touched the ground before the whole apparatus came down. Some labouring men were called up to help in extricating the mirror, which was fortunately uninjured, but much work was cut out for carpenters next day.”

In the following March, he himself wrote to Patrick Wilson, of Glasgow, son of Dr. Alexander Wilson, the well-known professor of astronomy:—“I have finished a second speculum to my new twenty-foot, very much superior to the first, and am now reviewing the heavens with it. This will be a work of some years; but it is to me so far from laborious that it is attended with the utmost delight.” He, nevertheless, looked upon telescopes as “yet in their infant state.”

The ruinous mansion at Datchet having become uninhabitable, even by astronomers, their establishment was shifted, in June, 1785, to Clay Hall, near Old Windsor. Here the long-thought-of forty-foot was begun, but was not destined to be finished. A litigious landlady intervened. The next move, however, proved to be the last. It was to a commodious residence at Slough, now called “Observatory House”—“le lieu du monde,” wrote Arago, “où il a été fait le plus de découvertes.” Thither, without the loss of an hour, in April, 1786, the machinery and apparatus collected at Clay Hall were transported. Yet, “amidst all this hurrying business,” Caroline remembered “that every moment after daylight was allotted to observing. The last night at Clay Hall was spent in sweeping till daylight, and by the next evening the telescope stood ready for observation at Slough.”

During the ensuing three months, thirty to forty workmen were constantly employed, “some in felling and rooting out trees, some in digging and preparing the ground for the bricklayers who were laying the foundation for the telescope.” “A whole troop of labourers” were, besides, engaged in reducing “the iron tools to a proper shape for the mirror to be ground upon.” Thus, each morning, when dawn compelled Herschel to desist from observation, he found a bevy of people awaiting instructions of all sorts from him. “If it had not been,” his sister says, “for the intervention of a cloudy or moonlit night, I know not when he, or I either, should have got any sleep.” The wash-house was turned into a forge for the manufacture of specially designed tools; heavy articles cast in London were brought by water to Windsor; the library was so encumbered with stores, models, and implements, that “no room for a desk or an atlas remained.”

On July 3rd, 1786, Herschel, accompanied by his brother Alexander, started for Göttingen, commissioned by the King to present to the University one of the ten-foot reflectors purchased from him. He was elected a Member of the Royal Society of Göttingen, and spent three weeks at Hanover with his aged mother, whom he never saw again. During his absence, however, the forty-foot progressed in accordance with the directions he had taken care to leave behind. He trusted nothing to chance. “There is not one screwbolt,” his sister asserted, “about the whole apparatus but what was fixed under the immediate eye of my brother. I have seen him lie stretched many an hour in a burning sun, across the top beam, whilst the iron-work for the various motions was being fixed. At one time no less than twenty-four men (twelve and twelve relieving each other) kept polishing day and night; my brother, of course, never leaving them all the while, taking his food without allowing himself time to sit down to table.”

At this stage of the undertaking it became the fashion with visitors to use the empty tube as a promenade. Dr. and Miss Burney called, in July, 1786, “to see, and take a walk through the immense new telescope.” “It held me quite upright,” the authoress of “Evelina” related, “and without the least inconvenience; so would it have done had I been dressed in feathers and a bell-hoop.”

George III. and the Archbishop of Canterbury followed the general example; and the prelate being incommoded by the darkness and the uncertain footing, the King, who was in front, turned back to help him, saying: “Come, my lord bishop, I will show you the way to heaven.” On another occasion “God save the King” was sung and played within the tube by a large body of musicians; and the rumour went abroad that it had been turned into a ball-room!

The University of Oxford conferred upon Herschel, in 1786, an honorary degree of LL.D.; but he cared little for such distinctions. Miss Burney characterised him as a “man without a wish that has its object in the terrestrial globe;” the King had “not a happier subject.” The royal bounty, she went on “enables him to put into execution all his wonderful projects, from which his expectations of future discoveries are so sanguine as to make his present existence a state of almost perfect enjoyment.” Nor was it possible to “admire his genius more than his gentleness.” Again, after taking tea in his company in the Queen’s lodge: “this very extraordinary man has not more fame to awaken curiosity than sense and modesty to gratify it. He is perfectly unassuming, yet openly happy; and happy in the success of those studies which would render a mind less excellently formed presumptuous and arrogant.” Mrs. Papendick, another court chronicler, says that “he was fascinating in his manner, and possessed a natural politeness, and the abilities of a superior nature.”

His great telescope took rank, before and after its completion, as the chief scientific wonder of the age. Slough was crowded with sightseers. All the ruck of Grand Dukes and Serene Highnesses from abroad, besides royal, noble, and gentle folk at home, flocked to gaze at it and interrogate its maker with ignorant or intelligent wonder. The Prince of Orange was a particularly lively inquirer. On one of his calls at Slough, about ten years after the erection of the forty-foot, finding the house vacant, he left a memorandum asking if it were true, as the newspapers reported, that “Mr. Herschel had discovered a new star whose light was not as that of the common stars, but with swallow-tails, as stars in embroidery?”!

Pilgrim-astronomers came, too—Cassini, Lalande, Méchain and Legendre from Paris, Oriani from Milan, Piazzi from Palermo. Sniadecki, director of the observatory of Cracow, “took lodgings,” Miss Herschel relates, “in Slough, for the purpose of seeing and hearing my brother whenever he could find him at leisure. He was a very silent man.” One cannot help fearing that he was also a very great bore. Von Magellan, another eminent foreign astronomer, communicated to Bode an interesting account of Herschel’s methods of observation. The multitude of entries in his books astonished him. In sweeping, he reported, “he lets each star pass at least three times through the field of his telescope, so that it is impossible that anything can escape him.” The thermometer in the garden stood that night, January 6th, 1785, at 13 deg. Fahrenheit; but the royal astronomer, his visitor remarked, “has an excellent constitution, and thinks about nothing else in the world but the celestial bodies.”

In January, 1787, Herschel made trial with his twenty-foot reflector of the “front-view” plan of construction, suggested by Lemaire in 1732, but never before practically tested. All that had to be done was to remove the small mirror, and slightly tilt the large one. The image was then formed close to the upper margin of the tube, into which the observer, turning his back to the heavens, looked down. The purpose of the arrangement was to save the light lost in the second reflection; and its advantage was at once illustrated by the discovery of two Uranian moons—one (Titania) circling round its primary in about 8¾ hours, the other (Oberon) in 13½ hours. In order to assure these conclusions, he made a sketch beforehand of what ought to be seen on February 10th; and on that night, to his intense satisfaction, “the heavens,” as he informed the Royal Society, “displayed the original of my drawing by showing, in the situation I had delineated them, the Georgian planet attended by two satellites. I confess that this scene appeared to me with additional beauty, the little secondary planets seeming to give a dignity to the primary one which raises it into a more conspicuous situation among the great bodies of our solar system.”

This brilliant result determined him to make a “front-view” of the forty-foot. Its advance towards completion was not without vicissitudes. The first speculum, when put into the tube, February 19th 1787, was found too thin to maintain its shape. A second, cast early in 1788, cracked in cooling. The same metal having been recast February 16th, the artist tried it upon Saturn in October; but the effect disappointing his expectation, he wrought at it for ten months longer. At last, after a few days’ polishing with his new machine, he turned the great speculum towards Windsor Castle; when its high quality became at once manifest. And such was his impatience to make with it a crucial experiment, that—as he told Sir Joseph Banks—he directed it to the heavens (August 28th, 1789) before it had half come to its proper lustre. The stars came out well, and no sooner had he got hold of Saturn than a sixth satellite stood revealed to view! Its “younger brother” was detected September 17th; and the two could be seen, on favourable opportunities, threading their way, like beads of light, along the lucid line of the almost vanished ring. Herschel named them Enceladus and Mimas, and found, on looking up his former observations of Saturn, that Enceladus, the exterior and brighter object, had been unmistakably seen with the twenty-foot, August 19th, 1787. Mimas is a very delicate test of instrumental perfection.

The mirror by which it was first shown measured nearly fifty inches across, and weighed 2,118 pounds. It was slung in a ring, and the sheet-iron tube in which it rested was thirty-nine and a-half feet long and four feet ten inches wide. Ladders fifty feet in length gave access to a movable stage, from which the observer communicated through speaking tubes with his assistants. The whole erection stood on a revolving platform; for the modern equatorial form of mount, by which the diurnal course of the heavens is automatically followed, was not then practically available, and the necessary movements had to be imparted by hand. This involved the attendance of two workmen, but was otherwise less inconvenient than might be supposed, owing to the skill with which the required mechanism was contrived.

Herschel estimated that, with a magnifying-power of 1,000, this grand instrument could, in the climate of England, be effectively used during no more than one hundred hours of every year. A review with it of the whole heavens would hence have occupied eight centuries. In point of fact, he found the opportunities for its employment scarce. The machine took some time to get started, while the twenty-foot was ready in ten minutes. The speculum, moreover, proved unpleasantly liable to become dewed in moist weather, or frozen up in cold; and, in spite of all imaginable care, it preserved the delicacy of its polish no more than two years. An economist of minutes, such as its maker, could, then, do no otherwise than let the giant telescope lie by unless its powers were expressly needed. They were surprisingly effective. “With the forty-foot instrument,” he reported to the Royal Society in 1800, “the appearance of Sirius announced itself at a great distance like the dawn of the morning, till this brilliant star at last entered the field, with all the splendour of the rising sun, and forced me to take my eye from that beautiful sight.” Which, however, left the vision impaired in delicacy for nigh upon half-an-hour.

Thus the results gathered from the realisation of Herschel’s crowning optical achievement fell vastly short of what his imagination had pictured. The promise of the telescope’s initial disclosures was not realised in its subsequent career. Yet it was a superb instrument. The discovery with it of Mimas gave certain proof that the figure of the speculum was as perfect as its dimensions were unusual. But its then inimitable definition probably fell off later. Its “broad bright eye” was, for the last time, turned towards the heavens January 19th, 1811, when the Orion nebula showed its silvery wings to considerable advantage. But incurable dimness had already set in—incurable, because the artist’s hand had no longer the strength needed to cure the growing malady. The big machine was, however, left standing, framework and all. It figured as a landmark on the Ordnance Survey Map of England; and, stamped in miniature on the seal of the Royal Astronomical Society, aptly serves to illustrate its motto, “Quicquid nitet notandum.” At last, on New Years Eve, 1839, the timbers of the scaffolding being dangerously decayed, it was, with due ceremony, dismounted. A “Requiem,” composed by Sir John Herschel, was sung by his family, fourteen in number, assembled within the tube, which was then riveted up and laid horizontally on three stone piers in the garden at Slough. “It looks very well in its new position,” Sir John thought. Yet it has something of a memento mori aspect. It seems to remind one that the loftiest human aspirations are sprinkled “with the dust of death.” The speculum adorns the hall of Observatory House.

Herschel married, May 8th, 1788, Mary, the only child of Mr. James Baldwin, a merchant in the City of London, and widow of Mr. John Pitt. She was thirty-eight and he fifty. Her jointure relieved him from pecuniary care, and her sweetness of disposition secured his domestic happiness. They set up a curious double establishment, taking a house at Upton, while retaining that at Slough. Two maidservants were kept in each, and a footman maintained the communications. So at least runs Mrs. Papendick’s gossip. Miss Burney records in her Diary a tea at Mr. De Luc’s, where Dr. Herschel accompanied a pair of vocalists “very sweetly on the violin. His newly-married wife was with him, and his sister. His wife seems good-natured; she was rich, too! And astronomers are as able as other men to discern that gold can glitter as well as stars.”

He was now at the height of prosperity and renown. Diplomas innumerable were showered upon him by Academies and learned societies. In a letter to Benjamin Franklin, he returned thanks for his election as a member of the American Philosophical Society, and acquainted him with his recent detection of a pair of attendants on the “Georgian planet.” A similar acknowledgment was addressed to the Princess Daschkoff, Directress of the Petersburg Academy of Sciences. The King of Poland sent him his portrait; the Empress Catherine II. opened negotiations for the purchase of some of his specula, Lucien Bonaparte repaired to Slough incognito; Joseph Haydn snatched a day from the turmoil of his London engagements to visit the musician-astronomer, and gaze at his monster telescopes. By universal agreement, Dr. Burney declared, Herschel was “one of the most pleasing and well-bred natural characters of the day, as well as the greatest astronomer.” They had much in common, according to Dr. Burney’s daughter. Both possessed an uncommon “suavity of disposition”; both loved music; and Dr. Burney had a “passionate inclination for astronomy.” They became friends through the medium of Dr. Burney’s versified history of that science. In September, 1797, he called at Slough with the manuscript in his valise. “The good soul was at dinner,” he relates; and, to his surprise, since he was ignorant of Herschel’s marriage, the company included several ladies, besides “a little boy.” He was, nothing loth, compelled to stay over-night; discussed with his host the plan of his work, and read to him its eighth chapter. Herschel listened with interest, and modestly owned to having learnt much from what he had heard; but presently dismayed the author by confessing his “aversion to poetry,” which he had generally regarded as “an arrangement of fine words without any adherence to the truth.” He added, however, that “when truth and science were united to those fine words,” they no longer displeased him. The readings continued at intervals, alternately at Slough and Chelsea, to the immense gratification of the copious versifier, who occasionally allowed his pleasure to overflow in his correspondence.

“Well, but Herschel has been in town,” he wrote from Chelsea College, December 10th, 1798, “for short spurts and back again, two or three times, and I have had him here two whole days. I read to him the first five books without any one objection.” And again; “He came, and his good wife accompanied him, and I read four and a-half books; and on parting, still more humble than before, or still more amiable, he thanked me for the instruction and entertainment I had given him. What say you to that? Can anything be grander?”

In spite of his “aversion,” Herschel had once, and once only, wooed the coy muse himself. The first evening paper that appeared in England, May 3rd, 1788, contained some introductory quatrains by him. An excuse for this unwonted outburst may be found in the circumstance that the sheet in which they were printed bore the name of The Star. They began with the interrogation:

“What Star art thou, about to gleam

In Novelty’s bright hemisphere?”

and continued:

“A Planet wilt thou roll sublime,

Spreading like Mercury thy rays?

Or chronicle the lapse of Time,

Wrapped in a Comet’s threatening blaze?”

That they are of the schoolboy order need surprise no one. Such a mere sip at the “Pierian spring” could scarcely bring inspiration.

Herschel’s grand survey of the heavens closed with his fourth review. His telescopic studies thereupon became specialised. The sun, the planets and their satellites, the lately discovered asteroids, certain double stars, and an occasional comet, in turn received attention. Laboratory experiments were also carried on, and discussions of profound importance were laid before the Royal Society. All this cost him but little effort. The high tension of his earlier life was somewhat relaxed; he allowed himself intervals of rest, and indulged in social and musical recreations. Concerts were now frequently given at his house; and the face of beaming delight with which he presided over them is still traditionally remembered. Visits to Sir William Watson at Dawlish gave him opportunities, otherwise rare, for talks on metaphysical subjects; and he stayed with James Watt at Heathfield in 1810. He had been a witness on his side in an action for infringement of patent in 1793.

Herschel rented a house on Sion Hill, Bath, for some months of the year 1799; and from time to time stayed with friends in London, or sought change of air at Tunbridge Wells, Brighton, or Ramsgate. In July, 1801, he went to Paris with his wife and son, made acquaintance with Laplace, and had an interview with the First Consul. It was currently reported that Bonaparte had astonished him by the extent of his astronomical learning; but the contrary was the truth. He had tried to be impressive, but failed. Herschel gave an account of what passed to the poet Campbell, whom he met at Brighton in 1813.

“The First Consul,” he said, “did surprise me by his quickness and versatility on all subjects; but in science he seemed to know little more than any well-educated gentleman; and of astronomy much less, for instance, than our own king. His general air was something like affecting to know more than he did know.” Herschel’s election in 1802 as one of the eight foreign Associates of the French Institute was probably connected with his Parisian experiences.

He inspired Campbell with the most lively enthusiasm. “His simplicity,” he wrote, “his kindness, his anecdotes, his readiness to explain—and make perfectly conspicuous too—his own sublime conceptions of the universe, are indescribably charming. He is seventy-six, but fresh and stout; and there he sat, nearest the door at his friend’s house, alternately smiling at a joke, or contentedly sitting without share or notice in the conversation. Any train of conversation he follows implicitly; anything you ask, he labours with a sort of boyish earnestness to explain. Speaking of himself, he said, with a modesty of manner which quite overcame me, when taken together with the greatness of the assertion, ‘I have looked further into space than ever human being did before me; I have observed stars, of which the light, it can be proved, must take two millions of years to reach this earth.’ I really and unfeignedly felt at the moment as if I had been conversing with a supernatural intelligence. ‘Nay, more,’ said he, ‘if those distant bodies had ceased to exist two millions of years ago we should still see them, as the light would travel after the body was gone.’ These were Herschel’s words; and if you had heard him speak them, you would not think he was apt to tell more than the truth.”

The appearance of a bright comet, in October, 1806, drew much company to Slough. On the 4th, Miss Herschel narrates, “Two parties from the Castle came to see it, and during the whole month my brother had not an evening to himself. As he was then in the midst of polishing the forty-foot mirror, rest became absolutely necessary after a day spent in that most laborious work; and it has ever been my opinion that on the 14th of October his nerves received a shock from which he never got the better afterwards; for on that day he had hardly dismissed his troop of men when visitors assembled, and from the time it was dark, till past midnight, he was on the grass-plot surrounded by between fifty and sixty persons, without having had time to put on proper clothing, or for the least nourishment to pass his lips. Among the company I remember were the Duke of Sussex, Prince Galitzin, Lord Darnley, a number of officers, Admiral Boston, and some ladies.”

A dangerous attack of illness in the spring of 1807 left Herschel’s strength permanently impaired. But he travelled to Scotland in the summer of 1810, and received the freedom of the City of Glasgow. Then, in 1814, he made a final, but fruitless attempt, to renovate the four-foot speculum. In the midst of the confusion attending upon the process, word was given to prepare for the reception of the Czar Alexander, the Duchess of Oldenburg, and sundry other grandees just then collected at Windsor for the Ascot races. The setting to rights was no small job; “but we might have saved ourselves the trouble,” his sister remarks drily, “for they were sufficiently harassed with public sights and festivities.”

On April 5th, 1816, Herschel was created a Knight of the Royal Hanoverian Guelphic Order, and duly attended one of the Prince Regent’s levées in May. He went to town in 1819 to have his portrait painted by Artaud. The resulting fine likeness is in the possession of his grandson, Sir William James Herschel. The Astronomical Society chose him as its first President in 1821; and he contributed to the first volume of its memoirs a supplementary list of 145 double stars. The wonderful series of his communications to the Royal Society closed when he was in his eightieth year, with the presentation, June 11th, 1818, of a paper on the Relative Distances of Star-clusters. On June 1st, 1821, he inserted into the tube with thin and trembling hands the mirror of the twenty-foot telescope, and took his final look at the heavens. All his old instincts were still alive, only the bodily power to carry out their behests was gone. An unparalleled career of achievement left him unsatisfied with what he had done. Old age brought him no Sabbath rest, but only an enforced and wearisome cessation from activity. His inability to re-polish the four-foot speculum was the doom of his chef d’œuvre. He could not reconcile himself to it. His sunny spirits gave way. The old happy and buoyant temperament became overcast with despondency. His strong nerves were at last shattered.

On August 15th, 1822, Miss Herschel relates:—“I hastened to the spot where I was wont to find him with the newspaper I was to read to him. But I was informed my brother had been obliged to return to his room, whither I flew immediately. Lady Herschel and the housekeeper were with him, administering everything which could be thought of for supporting him. I found him much irritated at not being able to grant Mr. Bulman’s[C] request for some token of remembrance for his father. As soon as he saw me, I was sent to the library to fetch one of his last papers and a plate of the forty-foot telescope. But for the universe I could not have looked twice at what I had snatched from the shelf, and when he faintly asked if the breaking-up of the Milky Way was in it, I said ‘Yes,’ and he looked content. I cannot help remembering this circumstance; it was the last time I was sent to the library on such an occasion. That the anxious care for his papers and workrooms never ended but with his life, was proved by his whispered inquiries if they were locked, and the key safe.”

[C] The grandson of one of Herschel’s earliest English friends.

He died ten days later, August 25th, 1822. Above his grave, in the church of Saint Laurence at Upton, the words are graven:—“Coelorum perrupit claustra”—He broke through the barriers of the skies.

William Herschel was endowed by nature with an almost faultless character. He had the fervour, without the irritability of genius; he was generous, genial, sincere; tolerant of ignorance; patient under the acute distress, to which his situation rendered him peculiarly liable, of unseasonable interruptions at critical moments: he was warm-hearted and open-handed. His change of country and condition, his absorption in science, the homage paid to him, never led him to forget the claims of kindred. Time and money were alike lavished in the relief of family necessities. He supported his brother Alexander after his retirement from the concert-stage in 1816, until his death at Hanover, March 15th, 1821. Dietrich’s recurring misfortunes met his unfailing pity and help. He bequeathed to him a sum of £2,000, and to his devoted sister, Caroline, an annuity of £100.

His correspondents, abroad and at home, were numerous; nor did he disdain to remove the perplexities of amateurs. In a letter, dated January 6th, 1794, we find him explaining to Mr. J. Miller of Lincoln’s Inn, “the circumstances which attend the motion of a race-horse upon a circle of longitude.” And he wrote shortly afterwards to Mr. Smith of Tewkesbury:—“You find fault with the principles of gravitation and projection because they will not account for the rotation of the planets upon their axes. You might certainly with as much reason find fault with your shoes because they will not likewise serve your hands as gloves. But, in my opinion, the projectile motion once admitted, sufficiently explains the rotatory motion; for it is hardly possible mechanically to impress the one without giving the other at the same time.”

On religious topics he was usually reticent; but a hint of the reverent spirit in which his researches were conducted may be gathered from a sentence in the same letter. “It is certainly,” he said, “a very laudable thing to receive instruction from the great workmaster of nature, and for that reason all experimental philosophy is instituted.”

To investigate was then, in his view, to “receive instruction”; and one of the secrets of his wonderful success lay in the docility with which he came to be taught.

CHAPTER III.
THE EXPLORER OF THE HEAVENS.

“A knowledge of the construction of the heavens,” Herschel wrote in 1811, “has always been the ultimate object of my observations.” The “Construction of the Heavens”! A phrase of profound and novel import, for the invention of which he was ridiculed by Brougham in the Edinburgh Review; yet expressing, as it had never been expressed before, the essential idea of sidereal astronomy. Speculation there had been as to the manner in which the stars were grouped together; but the touchstone of reality had yet to be applied to them. This unattempted, and all but impossible enterprise Herschel deliberately undertook. It presented itself spontaneously to his mind as worth the expenditure of a life’s labour; and he spared nothing in the disbursement. The hope of its accomplishment inspired his early exertions, carried him through innumerable difficulties, lent him audacity, fortified him in perseverance. For this,

“He left behind the painted buoy

That tosses at the harbour’s mouth,”

and burst his way into an unnavigated ocean.

Herschel has had very few equals in his strength of controlled imagination. He held the balance, even to a nicety, between the real and the ideal. Meditation served in him to prescribe and guide experience; experience to ripen the fruit of meditation.

“We ought,” he wrote in 1785, “to avoid two opposite extremes. If we indulge a fanciful imagination, and build worlds of our own, we must not wonder at our going wide from the path of truth and nature. On the other hand, if we add observation to observation without attempting to draw, not only certain conclusions, but also conjectural views from them, we offend against the very end for which only observations ought to be made.”

This was consistently his method. If thought outran sight, he laboured earnestly that it should be overtaken by it: while sight, in turn, often took the initiative, and suggested thought. He was much more than a simple explorer. “Even at the telescope,” Professor Holden says, “his object was not discovery merely, but to know the inner constitution of the heavens.” He divined, at the same time that he observed.

The antique conception of the heavens as a hollow sphere upon which the celestial bodies are seen projected, survived then, and survives now, as a convenient fiction for practical purposes. But in the eighteenth century the fiction assumed to the great majority a sort of quasi-reality. Herschel made an exception in being vividly impressed with the depth of space. How to sound that depth was the first problem that he attacked. As a preliminary to further operations, he sought to fix a unit of sidereal measurement. The distances from the earth to the stars were then altogether unknown. All that had been ascertained was that they must be very great. Instrumental refinements had not, in fact, been carried far enough to make the inquiry profitable. Herschel did not underrate its difficulty. He recognised that, in pursuing it, one hundredth of a second of arc “became a quantity to be considered.” Justly arguing, however, that previous experiments on stellar parallax had been unsatisfactory and indecisive, he determined to try again.

He chose the “double star method,” invented by Galileo, but never, so far, effectually put to trial. The principle of it is perfectly simple, depending upon the perspective shifting to a spectator in motion, of objects at different distances from him. In order to apprehend it, one need only walk up and down before a lamp placed in the middle of a room, watching its apparent change of position relative to another lamp at the end of the same room. Just in the same way, a star observed from opposite sides of the earth’s orbit is sometimes found to alter its situation very slightly by comparison with another star close to it in the sky, but indefinitely remote from it in space. Half the small oscillation thus executed is called that star’s “annual parallax.” It represents the minute angle under which the radius of the terrestrial orbit would appear at the star’s actual distance. So vast, however, is the scale of the universe, that this tell-tale swing to and fro is, for the most part, imperceptible even with modern appliances, and was entirely inaccessible to Herschel’s observations. Yet they did not remain barren of results.

“As soon as I was fully convinced,” he wrote in 1781, “that in the investigation of parallax the method of double stars would have many advantages above any other, it became necessary to look out for proper stars. This introduced a new series of observations. I resolved to examine every star in the heavens with the utmost attention that I might fix my observations upon those that would best answer my end. The subject promises so rich a harvest that I cannot help inviting every lover of astronomy to join with me in observations that must inevitably lead to new discoveries. I took some pains to find out what double stars had been recorded by astronomers; but my situation permitted me not to consult extensive libraries, nor, indeed, was it very material; for as I intended to view the heavens myself, Nature, that great volume, appeared to me to contain the best catalogue.”

On January 10th, 1782, he presented to the Royal Society a catalogue of 269 double stars, of which 227 were of his own finding; and a second list of 434 followed in December, 1784. All were arranged in six classes, according to the distance apart of their components, ranging from one up to 120 seconds. The close couples he regarded as especially adapted for parallax-determinations; the wider ones might serve for criteria of stellar proper movements, or even of the sun’s transport through space. For the purpose of measuring the directions in which their members lay towards each other—technically called “position-angles”—and the intervals separating them, he invented two kinds of micrometers, and notes were added as to their relative brightness and colours. He was the first to observe the lovely contrasted or harmonised tints displayed by some of these objects.

Herschel’s double stars actually fulfilled none of the functions assigned to them. He was thus left without any definite unit of measurement for sidereal space; and he never succeeded in supplying the want. In 1814 he was “still engaged,” though vainly, “in ascertaining a scale whereby the extent of the universe, so far as it is possible for us to penetrate into space, may be fathomed.” He knew only that the distances of the stars nearest the earth could not be less, and might be a great deal more, than light-waves, propagated at the rate of 186,300 miles a second, would traverse in three or four years. Only the manner of stellar arrangement, then, remained open to his zealous investigations.

The initial question presenting itself to an intelligent spectator of the nocturnal sky is: What relation does the dim galactic star-stream bear to the constellations amidst which it flows? And this question our interior position makes very difficult to be answered. We see the starry universe, it has been well said, “not in plan but in section.” The problem is, from that section to determine the plan—to view the whole mentally as it would show visually from the outside. The general appearance to ourselves of the Milky Way leaves it uncertain whether it represents the projection upon the heavens of an immense stratum of equally scattered stars, or a ring-like accumulation, towards the middle of which our sun is situated. Herschel gave his preference, to begin with, to the former hypothesis, and then, with astonishing boldness and ingenuity, attempted to put it experimentally to the proof.

His method of “star-gauging” was described in 1784. It consisted in counting the stars visible in successive fields of his twenty-foot telescope, and computing the corresponding depths of space. Admitting an average regularity of distribution, this was easily done. If the stars did not really lie closer together in one region than in another, then the more of them there were to be seen along a given line of vision, the further the system could be inferred to extend in that particular direction. The ratio of its extension would also be given. It would vary with the cube-roots of the number of stars in each count.

Guided by this principle, Herschel ventured to lay down the boundaries of the stellar aggregation to which our sun belongs. So far as he “had yet gone round it,” in 1785, he perceived it to be “everywhere terminated, and in most places very narrowly too.” The differences, however, between his enumerations in various portions of the sky were enormous. In the Milky Way zone the stars presented themselves in shoals. He met fields—of just one quarter the area of the moon—containing nearly 600; so that, in fifteen minutes, 116,000 were estimated to have marched past his stationary telescope. Here, the calculated “length of his sounding-line” was nearly 500 times the distance of Sirius, his standard star. Towards the galactic poles, on the contrary, stars were comparatively scarce; and the transparent blackness of the sky showed that in those quarters the supply of stars was completely exhausted. At right angles to the Milky Way, then, the stellar system might be termed shallow, while in its plane, it stretched out on all sides to an inconceivable, though not to an illimitable extent. Its shape appeared, accordingly, to be that of a flat disc, of very irregular contour, and with a deep cleft matching the bifid section of the Milky Way between Cygnus and Scorpio.

Herschel regarded this conclusion only “as an example to illustrate the method.” Yet it was derived from the reckoning-up of 90,000 stars in 2,400 telescopic fields! Its validity rested on the assumption that stellar crowding indicated, not more stars in a given space, but more space stocked in the same proportion with stars. But his hope of thus getting a true mean result collapsed under the weight of his own observations. “It would not be difficult,” he stated in 1785, “to point out two or three hundred gathering clusters in our system.” The action of a “clustering power” drawing its component stars “into many separate allotments” grew continually clearer to him, and he admitted unreservedly in 1802 that the Milky Way “consists of stars very differently scattered from those immediately about us.”

In 1811, he expressly abandoned his original hypothesis. “I must freely confess,” he wrote, “that by continuing my sweeps of the heavens my opinion of the arrangement of the stars has undergone a gradual change. An equal scattering of the stars may be admitted in certain calculations; but when we examine the Milky Way, or closely compressed clusters, it must be given up.”

And in 1817: “Gauges, which on a supposition of an equality of scattering, were looked upon as gauges of distance, relate, in fact, more immediately to the scattering of the stars, of which they give valuable information.”

The “disc-theory” was then virtually withdrawn not many years after it had been propounded. “The subtlety of nature,” according to Bacon’s aphorism, “transcends the subtlety both of the intellect and of the senses.” Herschel very soon perceived the inadequacy of his colossal experiment; and he tranquilly acquiesced, not being among those who seek to entrench theory against evidence. He found that he had undervalued the complexity of the problem. Yet it remained before his mind to the end. The supreme object of his scientific life was to ascertain the laws of stellar distribution in cubical space, and he devoted to the subject the two concluding memoirs of the sixty-nine contributed by him to the “Philosophical Transactions.” He was in his eightieth year when he opened, with youthful freshness, a new phase of arduous investigation.

“The construction of the heavens,” he wrote in June, 1817, “can only be known when we have the situation of each body defined by its three dimensions. Of these three, the ordinary catalogues give but two, leaving the distance or profundity undetermined.” This element of “profundity” he went on to determine by the absolutely novel method of what may be called “photometric enumeration.”

He began by asserting what is self-evident—that faint stars are, “one with another,” more remote than bright ones; and he argued thence, reasonably enough, that the relative mean distances of the stars, taken order by order, might be inferred from their relative mean magnitudes. Next he pointed out that more space would be available for their accommodation in proportion to the cubes of their mean distances. Here lies the value of the method. It sets up, as Herschel said, “a standard of reference” with regard to stellar distribution. It makes it possible to compare actual stellar density, at a given mean distance, with a “certain properly modified equality of scattering.” By patiently calling over the roll of successive magnitudes, information may be obtained regarding over- and under-populated districts of space.

Herschel’s reasonings on the subject are perfectly valid, but for practical purposes far in advance of the time. Their application demanded a knowledge of stellar light-gradations, which, even now, has been only partially attained. His surprising anticipation of this mode of inquiry came, therefore, to nothing.

His device of “limiting apertures” was a simultaneous invention. It was designed as a measure of relative star-distances. Pointing two similar telescopes upon two unequal stars, he equalised them to the eye by stopping down the aperture of the instrument directed towards the brighter object. Assuming each to emit the same quantity of light, their respective distances would then be inversely as the diameters of the reflecting surfaces by which they were brought to the same level of apparent lustre. But the enormous real diversities of stellar size and brightness render this plan of action wholly illusory. Even for average estimates, proper motion is apparently a safer criterion of distance than magnitude.

Herschel employed the method of apertures with better success to ascertain the comparative extent of natural and telescopic vision. The boundary of the former was placed at “the twelfth order of distance.” Sirius, that is to say, removed to twelve times its actual remoteness, would be a barely discernible object to the naked eye. The same star carried seventy-five times further away still, could be seen as a faint light-speck with his twenty-foot telescope; and, transported 192 times beyond the visual limit, would make a similar appearance in the field of the forty-foot. These figures, multiplied by twelve, represented, in his expressive phrase, the “space-penetrating power” of his instruments. Their range extended respectively to 900 and 2,300 times the distance of his “standard star.” He estimated, moreover, that, through the agency of the larger, light might become sensible to the eye after a journey lasting nearly seven thousand years! So that, as he said, his telescopes penetrated both time and space.

His last observation of the Milky Way showed it to be in parts “fathomless,” even with the forty-foot. No sky-background could be seen, but only the dim glow of “star-dust.” This effect he attributed to the immeasurable extension, in those directions, of the stellar system. The serried orbs composing it, as they lay further and further from the eye, became at last separately indistinguishable. Herschel, as has been said, formulated no second theory of galactic structure after that of 1784–5 had been given up. What he thought on the subject, with ripened experience for his guide, can only be gathered piecemeal from his various writings. The general appearance of

That “broad and ample road, whose dust is gold,

And pavement stars,”

he described as “that of a zone surrounding our situation in the solar system, in the shape of a succession of differently condensed patches of brightness, intermixed with others of a fainter tinge.” And he evidently considered this seeming to be in fair accord with reality. The “patches of brightness” stood for genuine clusters, incipient, visibly forming, or formed. They are made up of stars not less lustrous, but much more closely collected than Sirius, Arcturus, or Capella. The smallness of galactic stars would thus be an effect of distance, while their crowding is a physical fact. The whole of these clusters are (on Herschel’s view) aggregated into an irregular, branching ring, distinct from, although bound together into one system with the brilliants of the constellations. “Our sun,” he emphatically affirmed in 1817, “with all the stars we can see with the eye, are deeply immersed in the Milky Way, and form a component part of it.”

He took leave of the subject which had engrossed so many of his thoughts in a paper read before the Royal Society, June 11th, 1818. In it he showed how the “equalising” principle could be applied to determine the relative distances of “globular and other clusters,” provided only that their component stars are of the rank of Sirius. It is improbable, however, that this condition is fulfilled. In open groups, such as the Pleiades, enormous suns are most likely connected with minute self-luminous bodies; but the stars compressed into “globular clusters” appear to be more uniform, and may, perhaps, be intermediate in magnitude. Yet here again, the only thing certain is the prevalence of endless variety. Celestial systems are not turned out by the dozen, like articles from a factory. Each differs from the rest in scale, in structure, in mechanism. Attempts to reduce all to any common standard must then prove futile. Disparities of distance are of course concerned in producing their varieties of aspect, coarse-looking “balls of stars” being, necessarily, on the whole, less remote than those of smoother texture. Finer graining, however, may also be due to a composition out of smaller and closer masses. The two causes concur, and the share of each in producing a certain effect cannot, in any individual case, be apportioned.

Herschel was indeed far too philosophical to adopt rigid lines of argument. His reasoning did not extend “so far as to exclude a real difference, not only in the size, but also in the number and arrangement of the stars in different clusters.” Nevertheless, the discussion founded upon it is no longer convincing. To modern astronomers it appears to travel quite wide of the mark. Its interest consists in the proof given by it that the problem of sidereal distances, the original incentive to Herschel’s reviews of the heavens, attracted his attention to the very end of his thinking life. Throughout his long career, the profundities of the universe haunted him. He sought, per fas, per nefas, trustworthy measures of the “third dimension” of celestial space. The object of his search was out of reach, and has not even now been fully attained; but the path it led him by was strewn with discoveries.

The nets spread in his “sweeps” brought in, besides double stars, plentiful takes of the filmy objects called “nebulæ.” He recognised with amazement their profusion in certain tracts of the sky; increased telescopic light-grasp never failed to render a further supply visible; the heavens teemed with them. He presented a catalogue of 1,000 to the Royal Society in 1786, a second equally comprehensive in 1789, and a supplementary list of 500 in 1802. Their natural history fascinated him. What they were, what they had been, and what they should come to, formed the subject of many of those ardent meditations which supplied motive power for his researches. He not only laid the foundation of nebular science, but carried the edifice to a considerable height, distinguishing the varieties of its objects, and classifying them according to their gradations of brightness. Some presented a most fantastic appearance.

“I have seen,” he wrote in 1784, “double and treble nebulæ variously arranged; large ones with small, seeming attendants; narrow, but much extended lucid nebulæ or bright dashes; some of the shape of a fan, resembling an electric brush, issuing from a lucid point; others of the cometic shape, with a seeming nucleus in the centre, or like cloudy stars surrounded with a nebulous atmosphere; a different sort, again, contained a nebulosity of the milky kind, like that wonderful, inexplicable phenomenon about Theta Orionis; while others shine with a fainter mottled kind of light which denotes their being resolvable into stars.”

He, “through the mystic dome,” discerned

“Regions of lucid matter taking form,

Brushes of fire, hazy gleams,

Clusters and beds of worlds, and bee-like swarms

Of suns and starry streams.”

Annular and planetary nebulæ were as such, first described by him. “Among the curiosities of the heavens,” he announced in 1785, “should be placed a nebula that has a regular concentric dark spot in the middle, and is probably a ring of stars.” This was the famous annular nebula in Lyra, then a unique specimen, now the type of a class.

The planetary kind, so-called from their planet-like discs, were always more or less of an enigma to him. The vividness and uniformity of their light appeared to cut them off from true nebulæ; on mature consideration, he felt driven to suppose them “compressed star-groups.” “If it were not, perhaps, too hazardous,” he went on, “to pursue a former surmise of a renewal in what I figuratively called the laboratories of the universe, the stars forming these extraordinary nebulæ, by some decay or waste of nature, being no longer fit for their former purposes, and having their projectile forces, if any such they had, retarded in each other’s atmospheres, rush at last together, and either in succession, or by one general tremendous shock, unite into a new body. Perhaps the extraordinary and sudden blaze of a new star in Cassiopeia’s Chair, in 1572, might possibly be of such a nature.”

At that early stage of his inquiries, Herschel regarded all nebulæ indiscriminately as composed of genuine stars. It was almost inevitable that he should do so. For each gain in telescopic power had the effect of transferring no insignificant proportion of them from the nebular to the stellar order. There was no apparent reason for drawing a line anywhere. The inference seemed irresistible, that resolvability was simply a question of optical improvement. As Messier’s nébuleuses sans étoiles had yielded to Herschel’s telescopes, so—it might fairly be anticipated—the “milky” streaks and patches seen by Herschel would curdle into stars under the compulsion of the still mightier instruments of the future. He was led on—to use his own expressions in 1791—“by almost imperceptible degrees from evident clusters, such as the Pleiades, to spots without a trace of stellar formation, the gradations being so well connected as to leave no doubt that all these phenomena were equally stellar.” They were what Lambert and Kant had supposed them to be—island-universes, vast congeries of suns, independently organised, and of galactic rank. They were, each and all, glorious systems, barely escaping total submergence in the illimitable ocean of space. Under the influence of these grandiose ideas, Herschel told Miss Burney, in 1786, that with his “large twenty-foot” he had “discovered 1,500 universes!” Fifteen hundred “whole sidereal systems, some of which might well outvie our Milky Way in grandeur.”

His contemplations of the heavens showed him everywhere traces of progress—of progress rising towards perfection, then sinking into decay, though with a sure prospect of renovation. He was thus led to arrange the nebulæ in a presumed order of development. The signs of interior condensation traceable in nearly all, he attributed to the persistent action of central forces. Condensation, then, gave evidence of age. Aggregated stars drew closer and closer together with time. So that scattered or branching formations were to be regarded as at an early stage of systemic existence; globular clusters, as representing universes still in the prime of life; while objects of the planetary kind were set down as “very aged, and drawing on towards a period of change, or dissolution.”

Our own nebula he characterised as “a very extensive, branching congeries of many millions of stars,” bearing upon it “fewer marks of profound antiquity than the rest.” Yet, in certain regions, he found “reason to believe that the stars are now drawing towards various secondary centres, and will in time separate into different clusters.” As an example of the ravages of time upon the galactic structure, he adverted to a black opening, four degrees wide, in the Zodiacal Scorpion, bordered on the west by an exceedingly compact cluster (Messier’s No. 80), possibly formed, he thought, of stars drawn from the adjacent vacancy. The chasm was to him one of the most impressive of celestial phenomena. His sister preserved an indelible recollection of hearing him, in the course of his observations, after a long, awful silence, exclaim, “Hier ist wahrhaftig ein Loch im Himmel!” (Here, truly, is a hole in the sky); and he recurred to its examination night after night and year after year, without ever clearing up, to his complete satisfaction, the mystery of its origin. The cluster significantly located at its edge was lit up in 1860 by the outburst of a temporary star.

This was not the sole instance noted by Herschel of the conjunction of a chasm with a cluster; and chasms and clusters alike told the same story of dilapidation. He foresaw, accordingly, as inevitable, the eventual “breaking-up” of the Milky Way into many small, but independent nebulæ. “The state into which the incessant action of the clustering power has brought it at present,” he wrote in 1814, “is a kind of chronometer that may be used to measure the time of its past and future existence; and although we do not know the rate of going of this mysterious chronometer, it is, nevertheless, certain that since the breaking up of the Milky Way affords a proof that it cannot last for ever, it equally bears witness that its past duration cannot be admitted to be infinite.”

Thus the idea of estimating the relative “ages” of celestial objects—of arranging them according to their progress in development, originated with Herschel in 1789. “This method of viewing the heavens,” he added, “seems to throw them into a new kind of light. They are now seen to resemble a luxuriant garden which contains the greatest variety of productions in different flourishing beds; and one advantage we may at least reap from it is that we can, as it were, extend the range of our experience to an immense duration. For, is it not almost the same thing whether we live successively to witness the germination, blooming, foliage, fecundity, fading, withering, and corruption of a plant, or whether a vast number of specimens, selected from every stage through which the plant passes in the course of its existence, be brought at once to our view?”

But while he followed the line of continuity thus vividly traced, another crossing, and more or less interfering with it, opened out before him. The discovery of a star in Taurus, “surrounded with a faintly luminous atmosphere,” led him, in 1791, to revise his previous opinions regarding the nature of nebulæ. He was not at all ashamed of this fresh start. No fear of “committing himself” deterred him from imparting the thoughts that accompanied his multudinous observations. He felt committed to nothing but truth. He was advancing into an untrodden country. At every step he came upon unexpected points of view. The bugbear of inconsistency could not prevent him from taking advantage of each in turn to gain a wider prospect.

Until 1791 Herschel never doubted that gradations of distance fully accounted for gradations of nebular resolvability. He had been led on, he explained, by almost imperceptible degrees from evident clusters to spots without a trace of stellar formation, no break anywhere suggesting the possibility of a radical difference of constitution. “When I pursued these researches,” he went on, “I was in the situation of a natural philosopher who follows the various species of animals and insects from the height of their perfection down to the lowest ebb of life; when, arriving at the vegetable kingdom, he can scarcely point out to us the precise boundary where the animal ceases and the plant begins; and may even go so far as to suspect them not to be essentially different. But, recollecting himself, he compares, for instance, one of the human species to a tree, and all doubt upon the subject vanishes. In the same manner we pass by gentle steps from a coarse cluster to an object such as the nebula in Orion, where we are still inclined to remain in the once adopted idea of stars exceedingly remote and inconceivably crowded, as being the occasion of that remarkable appearance. It seems, therefore, to require a more dissimilar object to set us right again. A glance like that of the naturalist, who casts his eye from the perfect animal to the perfect vegetable, is wanting to remove the veil from the mind of the astronomer. The object I have mentioned above is the phenomenon that was wanting. View, for instance, the nineteenth cluster of my sixth class, and afterwards cast your eye on this cloudy star, and the result will be no less decisive than that of the naturalist. Our judgment, I venture to say, will be that the nebulosity about the star is not of a starry nature.”

In this manner he inferred the existence of real nebulous matter—of a “shining fluid” of unknown and unimaginable properties. Was it perhaps, he asked himself, a display of electrical illumination, like the aurora borealis, or did it rather resemble the “magnificent cone of the zodiacal light?” A boundless field of speculation was thrown open. “These nebulous stars,” he added, “may serve as a clue to unravel other mysterious phenomena.”

As their close allies, he now recognised planetary nebulæ, the “milkiness, or soft tint of their light,” agreeing much better with the supposition of a fluid, than of a stellar condition. And he rightly placed in the same category the Orion nebula, and certain “diffused nebulosities” which he had observed just to tarnish the sky over wide areas. These last might, he considered, be quite near the earth, and the object in Orion not more distant than perhaps an average second magnitude star.

The relations of the sidereal to the nebular “principle” exercised Herschel’s thoughts during many years. He had no sooner reasoned out the existence in interstellar space of a rarefied, self-luminous substance, than he began to interrogate himself as to its probable function. Nature was to him the expression of Supreme Reason. He could only conceive of her doings as directed towards an intelligible end. Hence his confidence that rational investigation must lead to truth.

Already in 1791 he hinted at the conclusion which he foresaw. The envelope of a “cloudy star” was, he declared, “more fit to produce a star by its condensation than to depend upon the star for its existence.” And the surmise was confirmed by his detection, in a planetary nebula, of a sharp nucleus, or “generating star,” possibly to be completed in time by the further accumulation of luminous matter.

His conjectures developed in 1811 into a formal theory. The cosmical fluid was met with in all stages of condensation. Nebulous tracts of almost evanescent lustre were connected in an unbroken series with slightly “burred” objects, wanting only a few last touches to make them finished stars. The extremes, as he said, had been, by his “critical examination of the nebulous system,” “connected by such nearly allied intermediate steps, as will make it highly probable that every succeeding state of the nebulous matter is the result of the action of gravitation upon it while in a foregoing one.”

In 1814 he traced the progress towards maturity of binary systems. Originating in double nebulæ incompletely dissevered—Siamese-twin objects, of which he had collected 139 examples—they next appeared as nebulously-connected stars, finally as a pair materially isolated, and linked together by the sole tie of gravitation. Scattered clusters represented, in his scheme of celestial progress, a state antecedent to that of globular clusters. “The still remaining irregularity of their arrangement,” he said, “additionally proves that the action of the clustering power has not been exerted long enough to produce a more artificial construction.” He made, too, the important admission that clusters apparently “in, or very near the Milky Way,” were truly part and parcel of that complex agglomeration.

But what of his “fifteen hundred universes,” which had now logically ceased to exist? The stellar and nebular “principles” had virtually coalesced; both were included in the galactic system. The question of “island universes” was accordingly left in abeyance; although Herschel certainly believed in 1818 that among the multitude of “ambiguous objects”—we should call them irresolvable nebulæ—many exterior firmaments were included. Yet what he had ascertained about the distribution of nebulæ should alone have sufficed to shatter this remnant of a conviction.

The fact became clear to him during the progress of his “sweeps” that nebulæ, to some extent, replace stars. He found them to occur in “parcels,” more or less embedded with stars, “beds” and “parcels” together being surrounded by blank spaces. This arrangement grew so familiar to him that he used to notify his assistant, when stars thinned out in the zone he was traversing, “to prepare for nebulæ.” A wider relationship, brought within view by the large scale of his labours, was defined by his fortunate habit of charting, for convenience of identification, each newly-discovered batch of nebulæ.

“A very remarkable circumstance,” he wrote in 1784, “attending the nebulæ and clusters of stars, is that they are arranged into strata, which seem to run on to a great length; and some of them I have already been able to pursue, so as to guess pretty well at their form and direction. It is probable enough that they may surround the whole apparent sphere of the heavens, not unlike the Milky Way.”

In the following year he spoke no longer of a zone, but of two vast groupings of nebulæ about the opposite poles of the Milky Way. That is to say, where stars are scarcest nebulæ are most abundant. The correspondence did not escape him; but he did not recognise its architectonic meaning. He had traced out the main plan of the stellar world; he had discovered, not merely thousands of nebulæ, but the nebular system; he had shown that stars and nebulæ were intimately associated; he had even made it clear that nebular distribution was governed by the lines of galactic structure. It only remained to draw the obvious inference that these related parts made up one whole—that no more than a single universe is laid open to human contemplation. This was done by Whewell thirty years after his death.

CHAPTER IV.
HERSCHEL’S SPECIAL INVESTIGATIONS.

Double stars were, when Herschel began to pay attention to them, regarded as mere chance productions. No suspicion was entertained that a real, physical bond united their components. Only the Jesuit astronomer, Christian Mayer, maintained that bright stars were often attended by faint ones; and since his observations were not such as to inspire much confidence, his assertions counted for very little. “In my opinion,” Herschel wrote in 1782, “it is much too soon to form any theories of small stars revolving round large ones.” He, indeed, probably even then, suspected that close equal stars formed genuine couples; but he waited, if so, for evidence of the connection. The chief subject of his experiments on parallax was Epsilon Boötis, an exquisitely tinted, unequal pair. But he soon became aware that either stellar parallax was elusively small, or that he was on the wrong track for detecting it. And, since his favourite stars have proved to be a binary combination, it was, of course, drawing water in a sieve to make one the test of perspective shifting in the other.

The number of Herschel’s double stars alone showed them to be integral parts of an express design. Such a crop of casualties was out of all reasonable question. And it was actually pointed out in 1784 by John Michell, a man of extraordinary sagacity, that the odds in favour of their physical union were truly “beyond arithmetic.”

Herschel meantime kept them under watch and ward, and after the lapse of a score of years found himself in a position to speak decisively. On July 1, 1802, he informed the Royal Society that “casual situations will not account for the multiplied phenomena of double stars,” adding, “I shall soon communicate a series of observations proving that many of them have already changed their situation in a progressive course, denoting a periodical revolution round each other.” A year later he amply fulfilled this pledge. Discussing in detail the displacements brought to light by his patient measurements, he made it clear that they could be accounted for only by supposing the six couples in question to be “real binary combinations, intimately held together by the bond of mutual attraction.” His conclusion was, in each case, ratified by subsequent observation. The stars instanced by him—Castor, Gamma Leonis, Epsilon Boötis, Delta Serpentis, Gamma Virginis, and Zeta Herculis—are all noted binaries. Not satisfied with establishing the fact, Herschel assigned the periods of their revolutions. But he could only do so on the hypothesis of circular motion, while the real orbits are highly elliptical. His estimates then went necessarily wide of the mark. For one pair only, he was able to use an observation anterior to his own. Bradley had roughly fixed, in 1759, the relative position of the components of Castor, the finest double star in the northern heavens; and the preservation of the record in Dr. Maskelyne’s note-book extended by twenty years the basis of Herschel’s conclusions regarding this system.

He continued, in 1803, his discussions of double stars; announced a leisurely circulation of both the pairs composing the typical “double-double star,” Epsilon Lyræ; and conjectured the union of the two into one grand whole—a forecast verified by the evidence of common proper motion. The Annus Magnus of the quadruple system cannot, according to Flammarion, be less than a million of years.

The discovery of binary stars was, in Arago’s phrase, “one with a future.” In itself an amazing revelation, it marked the beginning of a series of investigations of immense variety and importance. By it, a science of sidereal mechanics was shown to be possible; the sway of gravitation received an unlimited extension; and the perception of order, which is the precursor of knowledge, ranged at once over the whole visible creation. Herschel, it is true, had not the means of formally proving that stellar orbits are described in obedience to the Newtonian law. His affirmative assertion rested only on the analogy of the solar system. But the rightness of his judgment has never seriously been called in question.

His research into the transport of the solar system through space proved, as Bessel said, that the activity of his mind was independent of the stimulus supplied by his own observations. It was one of his most brilliant performances.

The detection of progressive star-movements was due to Halley. It was announced in 1718. The bright objects spangling the sky are then “fixed” only in name. “But if the proper motion of the stars be admitted,” asked Herschel, “who can deny that of our sun?” The same idea had occurred to several earlier astronomers, but only one, Tobias Mayer, of Göttingen, had tried to test it practically; and he had failed. “To discern the proper motion of the sun between so many other motions of the stars,” Herschel might well designate “an arduous task.” Yet it was not on that account to be neglected. The conditions of the problem were perfectly clear to him. If the sun alone were in motion, the stars should unanimously appear to drift backward from the “apex,” or point on the sphere towards which his journey was directed. The heavens would open out in front of his advance, and close up behind. The effect was compared by Mayer to the widening prospect and narrowing vista of trees to a man walking through a forest. On this supposition, the perspective displacements of any two stars sufficiently far apart in the sky would suffice to determine the solar apex. For it should coincide with the intersection of the two great circles continuing the directions of those displacements. But the question is far from being of this elementary nature. The stars are all flitting about on their own account, after—to our apprehension—a haphazard fashion. The sole element of general congruity traceable among them is that “systematic, or higher, parallax,” by which each of them is, according to a determinate proportion, inevitably affected. If this can be elicited, the line of the sun’s progress becomes at once known.

Herschel treated the subject in the simplest possible manner. Striking a balance between the proper motions of only seven stars, he deduced, in 1783, from simple geometrical considerations, an apex for the sun’s way, marked by the star Lambda Herculis. But while he seemed to proceed by rule, he was really led by the unerring instinct of genius. His mode of conducting an investigation, small in compass, yet almost inconceivably grand in import, distances praise. Its directness and apparent artlessness strike us dumb with wonder. Eminently suited to the materials at his command, it was summary, yet, within fairly narrow limits, secure. And the result has stood the test of time. It ranks, even now, as a valuable approximation to the truth. He himself regarded his essay as nothing more than an experimental effort. In a letter to Dr. Wilson, of Glasgow, he expressed his apprehensions lest his paper on the sun’s motion “might be too much out of the way to deserve the notice of astronomers.”

Provided with Maskelyne’s table of thirty-six proper motions, he resumed the subject in 1805. He now employed a graphical method, drawing great circles to represent the observed stellar movements, and planting his apex impartially in the midst of their intersections. It was, however, less happily located than that of 1783. The constellation Hercules again just included it; but it lay certainly too far west, and probably too far north. The memoir conveying the upshot of the research is, none the less, a masterpiece. Philosophy and common-sense have rarely been so fortunately blended as in this discussion. Without any mathematical apparatus, the plan of attack upon a recondite problem is expounded with the utmost generality and precision. The reasoning is strong and sure; intelligible to the ignorant, instructive to the learned.

In his earlier paper, Herschel, while venturing only to “offer a few distant hints” as to the rate of the sun’s travelling, expressed the opinion that it could “certainly not be less than that which the earth has in her annual orbit.” That is to say, his minimum estimate was then nineteen miles per second. A direct inquiry, on the other hand, convinced him, in 1806, that the solar motion, viewed at right angles from the distance of Sirius, would cover yearly an arc of 1″. 112. This he called “its quantity;” the corresponding velocity remained undetermined. We can, however, now, since the real distance of his assumed station has been determined, translate this angular value into a linear speed of about nine miles a second. The mean of his two estimates, or fourteen miles a second, probably differs little from the actual rate at which the solar system is being borne to its unimaginable destination.

His conclusions regarding the solar translation obtained little notice, and less acceptance from his contemporaries and immediate successors. His son rejected them as untrustworthy; Bessel, the greatest authority of his time in the science of “how the heavens move,” declared in 1818 that the sun’s apex might be situated in any other part of the sky with as much probability as in the constellation Hercules. Not until Argelander, by a strict treatment of multiplied and improved data, arrived in 1837 at practically the same result, did Herschel’s anticipatory efforts obtain the recognition they deserved. Scarcely in any department has there been put on record so well-directed a leap into the dark of coming discovery.

The systematic light-measurement of the stars began with the same untiring investigator. He described in 1796 the method since named that of “sequences,” and presented to the Royal Society the first of six Photometric Catalogues embracing nearly all the 2,935 stars in Flamsteed’s “British Catalogue.” They gave comparative brightnesses estimated with the naked eye; classification by magnitudes was put aside as vague and misleading. The “sequences” serving for their construction were lists of stars arranged, by repeated trials, in order of lustre, and rendered mutually comparable by the inclusion in each of a few members of the preceding series. Their combination into a catalogue was then easily effected. “Simple as my method is in principle,” he remarked, “it is very laborious in its progress.” On a restricted scale it is still employed for following the gradations of change in variable stars.

These researches lay, as Professor Holden expresses it, “directly on the line of Herschel’s main work.” The separation of the stars into light-ranks intimates at once something as to their distribution in space; but the intimations may prove deceptive unless the divisions be accurately established. Hence, stellar photometry is an indispensable adjunct to the study of sidereal construction. Herschel prosecuted the subject besides with a view to ascertaining the constancy of stellar lustre. He had been struck with singular discordances between magnitudes assigned at different dates. Not to mention stars obviously variable, there were others which seemed to be affected by a slow, secular waxing or waning. In some of the instances alleged by him, the alteration was no doubt fictitious—a record of antique errors; but there was a genuine residuum. Thus, the immemorially observed constituents of the Plough preserve no fixed order of relative brilliancy, now one, now another of the septett having, at sundry epochs, assumed the primacy; while a small star in the same group, Alcor, the “rider” of the second “horse,” has, in the course of a millennium, plainly thrown off some part of its former obscurity. The Arabs in the desert regarded it as a test of penetrating vision; and they were accustomed to oppose “Suhel” to “Suha” (Canopus to Alcor) as occupying respectively the highest and lowest posts in the celestial hierarchy. So that Vidit Alcor, at non lunam plenam, came to be a proverbial description of one keenly alive to trifles, but dull of apprehension for broad facts. Now, however, Alcor is an easy naked-eye object. One needs not be a “tailor of Breslau,” or a Siberian savage, to see it. The little star is unmistakably more luminous than of old.

An inversion of brilliancy between Castor and Pollux, and between the two leading stars in the Whale, is further generally admitted to have taken place during the eighteenth century. The prevalence of such vicissitudes was deeply impressive to Herschel, especially through their bearing upon the past and future history of our own planet. “If,” he said, “the similarity of stars with our sun be admitted, how necessary will it be to take notice of the fate of our neighbouring suns, in order to guess at that of our own. The star which we have dignified by the name of Sun may to-morrow begin to undergo a gradual decay of brightness, like Alpha Ceti, Alpha Draconis, Delta Ursæ Majoris, and many other diminishing stars. It may suddenly increase like the wonderful star in Cassiopeia, or gradually come on like Pollux, Beta Ceti, etc. And, lastly, it may turn into a periodical one of twenty-five days’ duration (the solar period of rotation), as Algol is one of three days, Delta Cephei of five days, etc.” He found it, accordingly, “perhaps the easiest way of accounting for past changes in climate to surmise that our sun has been formerly sometimes more, sometimes less, bright than it is at present.” Herschel attempted, in 1798, to analyse star-colours by means of a prism applied to the eye-glasses of his reflector. Nothing of moment could at that time come of such experiments; but they deserve to be remembered as a sort of premonition of future methods of research into the physical condition of the stars.

His attention to the sun might have been exclusive, so diligent was his scrutiny of its shining surface. Many of its peculiarities were first described by him, and none escaped him, except the “deeper deep,” or black nucleus of spots, detected by Dawes in 1852. The dusky “pores” and brilliant “nodules,” the corrugations, indentations, and ridges; the manifold aspects of spots, or “openings;” their “luminous shelving sides,” known as penumbræ; were all noted in detail, ranged in proper order, and studied in their mutual relations. Spots presented themselves to him as evident depressions in the luminous disc; faculæ, “so far from resembling torches,” appeared “like the shrivelled elevations upon a dried apple, extended in length, and most of them joined together, making waves, or waving lines.” Towards the north and south, he went on, “I see no faculæ; there is all over the sun a great unevenness, which has the appearance of a mixture of small points of an unequal light; but they are evidently a roughness of high and low parts.”

His theory of the solar constitution was a development of Wilson’s. It was clearly conceived, firmly held, and boldly put forward. The definite picturesqueness, moreover, of the language in which it was clothed, at once laid hold of the public imagination, and gave it a place in public favour from which it was dislodged only by the irresistible assaults of spectrum analysis.

The sun was regarded by Herschel as a cool dark body surrounded by an extensive atmosphere made up of various elastic fluids. Its upper stratum—Schröter named it the “photosphere”—was of cloud-like composition, and consisted of lucid matter precipitated from the elastic medium by which it was sustained. Its depth was estimated at two or three thousand miles, and the nature of its emissions suggested a comparison with the densest coruscations of the aurora borealis. Below lay a region of “planetary,” or protective clouds. Dense, opaque, and highly reflective, “they must add,” he said, “a most capital support to the splendour of the sun by throwing back so great a share of the brightness coming to them.” Their movements betrayed the action of vehement winds; and indeed the continual “luminous decompositions” producing the radiating shell, with the consequent regeneration of atmospheric gases beneath, “must unavoidably be attended with great agitations, such as with us might even be called hurricanes.” The formation and ascent of “empyreal gas” would cause, when moderate in quantity, pores, or small openings in the brilliant layers. But should it happen to be generated in uncommon quantities, “it will burst through the planetary regions of clouds, and thus will produce great openings; then, spreading itself above them, it will occasion large shallows, and, mixing afterwards gradually with other superior gases, it will promote the increase, and assist in the maintenance of the general luminous phenomena.”

The solid globe thus girt round with cloud and fire was depicted as a highly eligible place of residence. An equable climate, romantic scenery, luxuriant vegetation, smiling landscapes, were to be found there. It might, accordingly, be admitted without hesitation that “the sun was richly stored with inhabitants.” For the lucid shell visible from the exterior possessed, according to this theory, none of the all-consuming ardour now attributed to it. Its blaze was a superficial display; beneath, “the immense curtain of the planetary clouds was everywhere closely drawn” round a world perfectly accommodated to vital needs.

In order to reconcile this supposed state of things with the observed order of nature, it was suggested that traces of it subsist in the planets, “all of which, we have pretty good reason to believe, emit light in some degree.” The night-side illumination of Venus, the sinister glare of the eclipsed moon, the auroral glimmerings of the earth, were adduced as evidence to this effect. The contrast between the central body and its dependants was softened down to the utmost.

“The sun, viewed in this light,” Herschel wrote in 1794, “appears to be nothing else than a very eminent, large, and lucid planet, evidently the first, or, in strictness of speaking, the only primary one of our system; all others being truly secondary to it. Its similarity to the other globes of the solar system with regard to its solidity, its atmosphere, and its diversified surface; the rotation upon its axis, and the fall of heavy bodies, lead us on to suppose that it is also most probably inhabited, like the rest of the planets, by beings whose organs are adapted to the peculiar circumstances of that vast globe.”

To us, nearing the grey dawn of the twentieth century, the idea seems extravagant; it was, in the eighteenth, plausible and alluring. The philosophers of that age regarded the multiplicity of inhabited worlds as of axiomatic certainty. The widest possible diffusion of life followed, they held, as a corollary from the beneficence of the Creator; while their sense of economy rendered them intolerant of wasted globes. Herschel was then reluctant to attribute to the sun a purely altruistic existence. Only from the point of view of our small terrestrial egotism could so glorious a body figure as solely an attractive centre, and a focus of warmth and illumination to a group of planets. Besides, looking abroad through the universe, we see multitudes of stars which can exercise no ministerial functions. Those united to form compressed clusters, or simply joined in pairs, are unlikely, it was argued, to carry a train of satellites with them in their complex circlings. Unless, then, “we would make them mere useless brilliant points,” they must “exist for themselves,” and claim primary parts in the great cosmical life-drama.

Herschel’s sun is to us moderns a wholly fabulous body. Still, there is a fantastic magnificence about the conception so strongly realised by his powerful imagination. Moreover, its scientific value was by no means inconsiderable. It represented the first serious effort to co-ordinate solar phenomena; it implied the spontaneous action of some sort of machinery for the production of light and heat. Spots were associated with a circulatory process; the photosphere was portrayed under its true aspect. The persistence of its hollows and heights, its pores and rugosities, convinced Herschel that the lustrous substance composing it was “neither a liquid nor an elastic fluid,” which should at once subside into an unbroken level. “It exists, therefore,” he inferred, “in the manner of lucid clouds swimming in the transparent atmosphere of the sun.”

“The influence of this eminent body on the globe we inhabit,” he wrote, continuing the subject in 1801, “is so great, and so widely diffused, that it becomes almost a duty to study the operations which are carried on upon the solar surface.” This duty he fulfilled to perfection. His telescopic readings from the changeful solar disc were of extraordinary precision and comprehensiveness. They show his powers as an observer perhaps at their best. And, since reasoning was with him inseparable from seeing, the appearances he noted took, as if of their own accord, their proper places. The history of spots was completely traced. He recorded their birth by the enlargement of pores; their development and sub-division; established their connexion with faculous matter, piled up beside them like mountain-ranges round an Alpine lake, or flung across their cavities like blazing suspension-bridges; and watched finally their closing-up and effacement, not even omitting the post-mortem examination of the disturbances they left behind.

One of Herschel’s curiously original enterprises was his attempt to ascertain a possible connexion between solar and terrestrial physics. “I am now much inclined to believe,” he stated in 1801, “that openings with great shallows, ridges, nodules, and corrugations, may lead us to expect a copious emission of heat, and, therefore, mild seasons. And that, on the contrary, pores, small indentations, and a poor appearance of the luminous clouds, the absence of ridges and nodules, and of large openings and shallows, will denote a spare emission of heat, and may induce us to expect severe seasons. A constant observation of the sun with this view, and a proper information respecting the general mildness or severity of the seasons in all parts of the world, may bring this theory to perfection, or refute it, if it be not well founded.”

But the available data regarding weather-changes turning out to be exceedingly defective, he had recourse to the celebrated expedient of comparing the state of the sun in past years with the recorded prices of corn. Fully admitting the inadequacy of the criterion, he still thought that the sun being “the ultimate fountain of fertility, the subject may deserve a short investigation, especially as no other method is left for our choice.” He obtained, as the upshot, partial confirmation of the surmise that “some temporary defect of vegetation” ensued upon the subsidence of solar agitation. In plainer language, food-stuffs tended to become dear when sun-spots were few and small. No signs of cyclical change could, however, be made out. The discovery of the “sun-spot period” was left to Schwabe. This admirable preliminary effort to elicit the earth’s response to solar vicissitudes was denounced by Brougham as a “grand absurdity;” and the readers of the second number of the Edinburgh Review were assured that “since the publication of ‘Gulliver’s Travels,’ nothing so ridiculous had ever been offered to the world!”

Herschel did not neglect the planets. His observations of Venus extended from 1777 to 1793. Their principal object was to ascertain the circumstances of the planet’s rotation; but they eluded him; which, considering that they are still quite uncertain, is not surprising. He would probably have communicated nothing on the subject had he not been piqued into premature publication by Schröter’s statement that the mountains of Venus rose to “four, five, or even six times the perpendicular elevation of Chimborazo.” Herschel did not believe in them, and expressed his incredulity in somewhat sarcastic terms. “As to the mountains in Venus,” he wrote, “I may venture to say that no eye which is not considerably better than mine, or assisted by much better instruments, will ever get a sight of them.” He rightly inferred, however, the presence of an extensive atmosphere from the bending of the sun’s rays so as to form much more than a semicircular rim of light to the dark disc of the planet when near inferior conjunction—that is, when approximately in a right line between us and the sun. He fully ascertained, too, the unreality of the Cytherean phantom-satellite. The irritability visible in this paper made a solitary exception to Herschel’s customary geniality. It might have led to a heated controversy but for the excellent temper of Schröter’s reply.

Although we may not be prepared to gainsay Herschel’s dictum that “the analogy between Mars and the earth is perhaps by far the greatest in the whole solar system,” we can hardly hold it to be so probable as he did that “its inhabitants enjoy a situation in many respects similar to ours.” Yet the modern epoch in the physical study of Mars began with his announcement in 1784 that its white polar caps spread and shrank as winter and summer alternated in their respective hemispheres. His conclusion of their being produced by snowy depositions from “a considerable, though moderate, atmosphere,” is not likely to be overthrown. He established, besides, the general permanence of the dark markings, notwithstanding minor alterations due, he supposed, to the variable distribution of clouds and vapours on the planet’s surface.

This vigilant “watcher of the skies” laid before the Royal Society, May 6th, 1802, his “Observations of the two lately discovered Bodies.” These were Ceres and Pallas, which, with Juno and Vesta, picked up shortly afterwards, constituted the vanguard of the planetoid army. Herschel foresaw its arrival. He adopted unhesitatingly Olbers’s theory of their disruptive origin, and calculated that Mercury, the least of the true planets, might be broken up into 35,000 masses no larger than Pallas. An indefinite number of such fragments (about 420 are now known) were accordingly inferred to circulate between the orbits of Mars and Jupiter. He distinguished their peculiarities, and, since they could with propriety be designated neither planets nor comets, he proposed for them the name of “asteroids.” But here again he incurred, to use his own mild phrase, “the illiberal criticism of the Edinburgh Review.” “Dr. Herschel’s passion for coining words and idioms,” Brougham declared, “has often struck us as a weakness wholly unworthy of him. The invention of a name is but a poor achievement in him who has discovered whole worlds.” The reviewer forgot, however, that new things will not always fit into the framework of old terminology. He added the contemptible insinuation that Herschel had devised the word “asteroid” for the express purpose of keeping Piazzi’s and Olbers’s discoveries on a lower level than his own of Uranus.

Herschel made no direct reply to the attack; only pointing out, in December, 1804, how aptly the detection of Juno had come to verify his forecasts. “The specific differences,” he said, “between planets and asteroids appear now, by the addition of a third individual of the latter species, to be more fully established; and that circumstance, in my opinion, has added more to the ornament of our system than the discovery of another planet could have done.”

His endeavours to determine the diameters of these small bodies were ineffectual. Although he at first estimated those of Ceres and Pallas at 162 and 147 miles, he admitted later his inability to decide as to the reality of the minute discs shown by them; and they were first genuinely measured by Professor Barnard with the great Lick refractor in 1894.

The “trade-wind theory” of Jupiter’s belts originated with Herschel; and he took note of the irregular drifting movements of the spots on his surface, and their consequent uselessness for determining the period of his rotation. That of Saturn’s he fixed quite accurately at ten hours sixteen minutes, with a marginal uncertainty of two minutes, the period now accepted being of ten hours fourteen minutes. The possession by this planet of a profound atmosphere was inferred from the changes in its belts, as well as from some curious phenomena attending the disappearance of its satellites. They were commonly seen to “hang on the limb”—that is, to pause during an appreciable interval on the brink of occultation. Mimas, on one occasion, remained thus poised during twenty minutes! For so long it was geometrically concealed, although visible by the effect of refraction. Saturn was an object of constant solicitude at Slough; and it was only with the surpassing instruments mounted there that much could be learned about Galileo’s altissimo pianeta. Herschel supposed, with Laplace, the rings to be solid structures; and he added that the interval of 2,500 miles separating them “must be of considerable service to the planet in reducing the space that is eclipsed by the shadow of the ring.” The “crape ring” was seen, but not recognised. In one of his drawings it figures as a dusky belt crossing the body of the planet.

His satellite discoveries proved exceedingly difficult to verify. The Saturnian pair were lost, after he left them, until his son once more drew them from obscurity. Regarding the outermost member of the system, Japetus, discovered by Cassini in 1671, Herschel noticed, in 1792, a singular circumstance. It was already known to vary in brightness; we receive from it, in fact, four and a-half times more light at certain epochs than at others. The novelty consisted in showing that this variation depended upon the satellite’s situation in its orbit in such a manner as to leave no doubt that, like our moon, it keeps the same face always directed inwards towards its primary. So that Japetus was inferred to turn on its axis in the period of its revolution round Saturn, that is, in seventy-nine and one-third days.

“From its changes” he “concluded that by far the largest part of its surface reflects much less light than the rest; and that neither the darkest nor the brightest side of the satellite is turned towards the planet, but partly the one and partly the other.”

Guessing at once that our moon and Japetus did not present the only examples of equality in the times of rotation and revolution, he continued: “I cannot help reflecting with some pleasure on the discovery of an analogy which shows that a certain uniform plan is carried on among the secondaries of our solar system; and we may conjecture that probably most of the satellites are governed by the same law, especially if it be founded upon such a construction of their figure as makes them more ponderous towards their primary planet.” This very explanation was long afterwards adopted by Hansen. The peculiarity in question may without hesitation be set down as an effect of primordial tides.

In 1797 Herschel brought forward detailed evidence to shew that his generalisation applied to the Jovian system; but recent observations at Lick and Arequipa demand a suspension of judgment on the point.

The Uranian train of attendants was left by Herschel in an unsettled condition. Two of them, as we have seen, he discovered in 1787; and he subsequently caught glimpses of what he took to be four others. But only Oberon and Titania have maintained their status; the four companions assigned to them are non-existent. An unmistakable interior pair—Ariel and Umbriel—was, however, discovered by Mr. Lassell, at Malta, in 1851; and they may possibly have combined with deceptive star-points to produce Herschel’s dubious quartette. He described in 1798 the exceptional arrangement of the Uranian system. Its circulation is retrograde. The bodies composing it move from east to west, but in orbits so tilted as to deviate but slightly from perpendicularity to the plane of the ecliptic.

No trifling sensation was created in 1783, and again in 1787, by the news that Herschel had seen three lunar volcanoes in violent eruption. “The appearance of the actual fire” in one of them was compared by him to “a small piece of burning charcoal when it is covered with a very thin coating of white ashes. All the adjacent parts of the volcanic mountain seemed to be faintly illuminated by the eruption, and were gradually more obscure as they lay at a greater distance from the crater.” He eventually became aware that his senses had imposed upon him; but the illusion was very complete and has since occasionally been repeated. What was really seen was probably the vivid reflection of earth-shine from some unusually white lunar summits.

He never knowingly discovered a comet, although some few such bodies possibly ensconced themselves, under false pretences, in his lists of nebulæ. But he made valuable observations upon the chief of those visible in his time, and introduced the useful terms, corresponding to instructive distinctions, “head,” “nucleus,” and “coma.” He inferred from the partial phases of the comet of 1807, that it was in a measure self-luminous; and from their total absence in the great comet of 1811, that its light was almost wholly original. The head of this object, which shone with an even, planetary radiance, he determined to be 127,000, the star-like nucleus within, 428 miles across. The tail he described as “a hollow, inverted cone,” one hundred millions of miles long, and fifteen millions broad. This prodigious appurtenance was, in grade of luminosity, an exact match for the Milky Way. That comets wear out by the waste of their substance at perihelion, he thought very probable; the extent of their gleaming appendages thus serving as a criterion of their antiquity. They might, indeed, arrive in the solar system already shorn of much of their splendour by passages round other suns than ours; but their “age” could, in any case, be estimated according to the progress made in their decline from a purely nebulous to an almost “planetary” state. He went so far as to throw out the conjecture that “comets may become asteroids;” although the converse proposition that “asteroids may become comets,” of which something has been heard lately, would scarcely have been entertained by him.

Enough has been said to show how greatly knowledge of the solar system in all its parts was furthered by Herschel’s observational resources, fertility of invention, and indomitable energy. He was, so to speak, ubiquitous. He had taken all the heavens for his province. Nothing that they included, from the faintest nebula to the sun, and from the sun to a telescopic shooting-star, evaded his consideration. A whole cycle of discoveries and successful investigations began and ended with him.

His fame as an astronomer has cast into the shade his merits as a physicist. He made pioneering experiments on the infra-red heat-rays,[D] and anticipated, by an admirable intuition, the fact ascertained with the aid of Professor Langley’s “bolometer,” that the invisible surpass in extent the visible portions of the solar spectrum.[E] A search for darkening glasses suitable to solar observations, led him to the inquiry. Finding that some coloured media transmitted much heat and little light, while others stopped heat and let through most of the light, he surmised that a different heating power might belong to each spectral tint. His own maxim that “it is sometimes of great use in natural philosophy to doubt of things that are commonly taken for granted,” here came in appropriately. With a free mind he set about determining the luminous and thermal powers of successive spectral regions. They seemed to vary quite disconnectedly. A thermometer exposed to red rays during a given interval, rose three and a half times as much as when exposed to violet rays; and he showed further, by tracing the heat- and light-curves of the prismatic spectrum, that its heat-maximum lay out of reach of the eye in the infra-red, while luminous intensity culminated in the yellow. He even threw out the sagacious conjecture that “the chemical properties of the prismatic colours” might be “as different as those which relate to light and heat;” adding that “we cannot too minutely enter into an analysis of light, which is the most subtle of all the active principles that are concerned in the operations of nature.”

[D] Phil. Trans. 1800, p. 255.

[E] Ibid., p. 291.

The ardour with which he pursued the inquiry betrays itself in the rapid succession of four masterly essays communicated to the Royal Society in 1800. They contained the first exposition worth mentioning of the properties of radiant heat. They gave the details of experiments demonstrating its obedience to the same laws of reflection, refraction, and dispersion as light; and showing the varieties in the absorptive action upon it of different substances. In the third memoir of the series, Professor Holden finds himself at a loss “which to admire most—the marvellous skill evinced in acquiring such accurate data with such inadequate means, and in varying and testing such a number of questions as were suggested in the course of the investigation—or the intellectual power shown in marshalling and reducing to a system such intricate, and apparently self-contradictory phenomena.” There is, indeed, scarcely one of Herschel’s researches in which his initiative vigour and insight are more brilliantly displayed than in this parergon—this task executed, as it were, out of hours. It is only a pity that he felt compelled, by the incompatibility of their distribution in the spectrum, to abandon his original opinion in favour of the essential identity of light and radiant heat. The erroneous impression left on the public mind by his recantation has hardly yet been altogether effaced.

CHAPTER V.
THE INFLUENCE OF HERSCHEL’S CAREER ON MODERN ASTRONOMY.

The powers of the telescope were so unexpectedly increased, that they may almost be said to have been discovered by William Herschel. No one before him had considered the advantages of large apertures. No one had seemed to remember that the primary function of an instrument designed to aid vision is to collect light. The elementary principle of space-penetration had not been adverted to. It devolved upon him to point out that the distances of similar objects are exactly proportional to the size of the telescopes barely sufficing to show them. The reason is obvious. Compare, for instance, a one-inch telescope with the naked eye. The telescope brings to a focus twenty-five times as much light as can enter the pupil, taken at one-fifth of an inch in diameter; therefore it will render visible a star twenty-five times fainter than the smallest seen without its help; or—what comes to the same thing—an intrinsically equal star at a five-fold distance. A one-inch glass hence actually quintuples the diameter of the visible universe, and gives access to seventy-five times the volume of space ranged through by the unassisted eye.

This simple law Herschel made the foundation-stone of his sidereal edifice. He was the first to notice it, because he was the first practically to concern himself with the star-depths. The possibility of gauging the heavens rose with him above the horizon of science. Because untiring in exploration, he was insatiable of light; and being insatiable of light, he built great telescopes.

His example was inevitably imitated and surpassed. Not through a vulgar ambition to “beat the record,” but because a realm had been thrown open which astronomers could not but desire to visit and search through for themselves. Lord Rosse’s six-foot reflector was the immediate successor of Herschel’s four-foot; Mr. Lassell’s beautiful specula followed; and the series of large metallic reflectors virtually closed with that of four-feet aperture erected at Melbourne in 1870. The reflecting surface in modern instruments is furnished by a thin film of silver deposited on glass. It has the advantage of returning about half as much again of the incident light as the old specula, so that equal power is obtained with less size. Dr. Common’s five-foot is the grand exemplar in this kind; and it is fully equivalent to the Parsonstown six-foot.

The improvement of refractors proceeded more slowly. Difficulties in the manufacture of glass stood in the way, and difficulties in the correction of colour. The splendid success, however, of the Lick thirty-six inch, and the fine promise of the Yerkes forty-inch, have turned the strongest current of hope for the future in the direction of this class of instrument. But all modern efforts to widen telescopic capacity primarily derive their impulse from Herschel’s passionate desire to see further, and to see better, than his predecessors.

His observations demonstrate the rare excellence of his instruments. Experiments made on the asteroid Juno, in 1805, for the purpose of establishing a valid distinction between real and fictitious star-discs, prove, in Professor Holden’s opinion, the reflector employed to have been of almost ideal perfection; and his following of Saturn’s inner satellites right up to the limb, with the twenty-foot and the forty-foot, was a tour de force in vision scarcely, if ever, surpassed.

In the ordinary telescopes of those days really good definition was unknown; they showed the stars with rays or tails, distorted into triangles, or bulged into “cocked hats;” clean-cut, circular images were out of the question. Sitting next Herschel one day at dinner, Henry Cavendish, the great chemist, a remarkably taciturn man, broke silence with the abrupt question—“Is it true, Dr. Herschel, that you see the stars round?” “Round as a button,” replied the Doctor; and no more was said until Cavendish, near the close of the repast, repeated interrogatively, “Round as a button?” “Round as a button,” Herschel briskly reiterated, and the conversation closed.

It seems probable that Herschel’s caput artis lost some of its fine qualities with time. Great specula are peculiarly liable to deterioration. Their figure tends to become impaired by the stress of their own weight; their lustre is necessarily more or less evanescent. Re-polishing, however, is a sort of re-making; and the last felicitous touches, upon which everything depends, can never be reckoned upon with certainty. Hence, the original faultlessness of the great mirror was, perhaps, never subsequently reproduced.

“Such telescopes as Herschel worked with,” Dr. Kitchiner wrote in 1815, “could only be made by the man who used them, and only be used by the man who made them.” The saying is strictly true. His skill in one branch promoted his success in the other. He was as much at home with his telescopes as the Bedouin are with their horses. Their peculiarities made part of his most intimate experience. From the graduated varieties of his specula he picked out the one best suited to the purpose in hand. It was his principle never to employ a larger instrument than was necessary, agility of movement being taken into account no less than capacity for collecting light. The time-element, indeed, always entered into his calculations; he worked like a man who has few to-morrows.

His sense of sight was exceedingly refined, and he took care to keep it so. In order to secure complete “tranquility of the retina,” he used to remain twenty minutes in the dark before attempting to observe faint objects; and his eye became so sensitive after some hours spent in “sweeping,” that the approach of a third-magnitude star obliged him to withdraw it from the telescope. A black hood thrown over his head while observing served to heighten this delicacy of vision. He despised no precaution. Details are “of consequence,” he wrote to Alexander Aubert, an amateur astronomer, “when we come to refinements, and want to screw an instrument up to the utmost pitch.”

This was said in reference to his application of what seemed extravagantly high magnifying powers. He laid great stress upon it in the earlier part of his career. The method, he said, was “an untrodden path,” in which “a variety of new phenomena may be expected.” With his seven-foot Newtonian he used magnifications up to nearly 6,000, proceeding, however, “all along experimentally”—a plan far too much neglected in “the art of seeing.” “We are told,” he proceeded, “that we gain nothing by magnifying too much. I grant it, but shall never believe I magnify too much till by experience I find that I can see better with a lower power.” The innovation was received with a mixture of wonder, incredulity, and admiration.

Herschel showed his customary judgment in this branch of astronomical practice. He established the distinctions still maintained, and laid down the lines still followed. It is true he went far beyond the point where modern observers find it advisable to stop. The highest power brought into use with the Lick refractor is 2,600; and Herschel’s instruments bore 5,800 (nominally 6,500) without injury to definition. But only at exceptional moments. His habitual sweeping power was 460; he “screwed-up” higher only for particular purposes, and under favourable conditions. Although his strong eye-pieces seem, for intelligible reasons, to have been laid aside on the adoption of the “front-view” form of construction, they had served him well in the division of close pairs, as well as for bringing faint stars into view—an effect correctly explained by him as due to the augmented darkness, under high powers, of the sky-ground. But the most important result of their employment was the discovery that the stars have no sensible dimensions. This became evident through the failure of attempts to magnify them; the higher the power applied, the smaller and more intense they appeared. Herschel accordingly pronounced stellar telescopic discs “spurious,” but made no attempt to explain their origin through diffraction.

He never possessed an instrument mounted equatoreally—that is, so as automatically to follow the stars. In its absence, his work, had it not been accomplished, would have seemed to modern ideas impossible. No clockwork movement kept the objects he was observing in the field of view. His hands were continually engaged in supplying the deficiency. How, under these circumstances, he contrived to measure hundreds of double stars, and secure the places of thousands of nebulæ, would be incomprehensible but for the quasi-omnipotence of enthusiasm.

The angle made with the meridian by the line joining two stars (their “position angle”) was never thought of as a quantity useful to be ascertained until Herschel, about 1779, invented his “revolving-wire micrometer.” This differed in no important respect from the modern “filar micrometer;” only spider-lines have been substituted for the original silk fibres. For measuring the distances of the wider classes of double stars, he devised in 1782 a “lamp-micrometer;” while those of the closest pairs were estimated in terms of the discs of the components. In compiling his second catalogue, however, he used the thread-micrometer for both purposes. It is true that “even in his matchless hands”—in Dr. Gill’s phrase—the results obtained were “crude;” but the fact remains that the whole system of micrometrical measurement came into existence through Herschel’s double-star determinations.

Their consequences have developed enormously within the last few years. Mr. Burnham’s discoveries of excessively close pairs have been so numerous as to leave no reasonable doubt that their indefinite multiplication is only a question of telescopic possibility. Then in 1889, another power came into play; the spectroscope took up the work of resolving stars. Or rather, the spectroscope in alliance with the photographic camera; for the spectral changes indicating the direction and velocity of motion in the line of sight can be systematically studied, as a rule, only when registered on sensitive plates. The upshot has been to bring within the cognisance of science the marvellous systems known as “spectroscopic binaries.” They are of great variety. Some consist of a bright, others of a bright and dark, pair. Those that revolve in a plane nearly coinciding with our line of vision undergo mutual occultations. A further detachment seem to escape eclipse, yet vary in light for some unexplained reason, while they revolve. Others, like Spica Virginis, revolve without varying. Their orbital periods are counted by hours or days. The study of the disturbances of these remarkable combinations promises to open a new era in astronomical theory. For they are most likely all multiple. Irregularities indicating the presence of attractive, although obscure bodies, have, in several cases, been already noticed.

The revolutions of spectroscopic binary stars can be studied to the greatest advantage when they involve light-change; and photometric methods have accordingly begun to play an important part in the sidereal department of gravitational science. And here again we meet with Herschel’s initiative. His method of sequences has been already explained; and he made the first attempt to lay down a definite scale of star-magnitudes. He failed, and it was hardly desirable that he should succeed. On his scale, the ratio of change from one grade to the next constantly diminished. In the modern system it remains always the same. A star of the second magnitude is by definition two and a-half (2·512) times less bright than one of the first; a star of the third magnitude is two and a-half times less bright than one of the second, the series descending without modification until beyond telescopic reach. This uniformity in the proportionate value of a magnitude is indispensable for securing a practicable standard of measurement. Herschel, however, took the great step of introducing a principle of order.

His estimates of stellar lustre were purely visual. And although various instruments, devised for the purpose, have since proved eminently useful, the ultimate appeal in all is to the eye. But there are many signs that, in the photometry of the future, not the eye but the camera will be consulted. Their appraisements differ markedly. Herschel’s incidental remark on the disturbance of light-valuation by colour touches a point of fundamental importance in photographic photometry. The chemical method gives to white stars a great advantage over yellow and red ones. They come out proportionately much brighter on the sensitive plate than they appear to the eye. And to these varieties of hue correspond spectral class-distinctions, the spectrum of an object being nothing but its colour written at full length. This systematic discrepancy between visual and photographic impressions of brightness, while introducing unwelcome complications in measures of magnitude, may serve to bring out important truths. The inference, for example, has been founded upon it that the Milky Way is composed almost exclusively of white, or “Sirian” stars; and there can be no question but that the arrangement of stars in space has some respect to their spectral types.

Herschel’s plan of inquiry into the laws of stellar distribution by “photometric enumeration,” or gauging by magnitudes, was a bequest to posterity which has been turned to account with very little acknowledgment of its source. Argelander’s review of the northern heavens (lately completed photographically by Dr. Gill to the southern pole) afforded, from 1862, materials for its application on a large scale; but the magnitudes assigned to his 324,000 stars do not possess the regularity needed to make deductions based on them perfectly trustworthy. Otherwise the distance from the earth of the actual aggregations in the Milky Way could have been ascertained in a rough way from the numerical representation of the various photometric classes. As it is, the presumption is strong that the galactic clouds are wholly independent of stars brighter than the ninth magnitude—that they only begin to gather at a depth in space whence light takes at least a thousand years to travel to our eyes. Confirmatory evidence, published in 1894, has been supplied by M. Easton’s research, based on the same principle, into the detailed relations of stars of various magnitudes to Milky Way structure. They are exhibited only by those of the ninth magnitude, or fainter; for with them sets in a significant crowding upon its condensed parts, attended by a scarcity over its comparative vacuities. Counts by magnitudes have, besides, made it clear that the stars, in portions of the sky removed from the Milky Way, thin out notably before the eleventh magnitude is reached; so that, outside the galactic zone, the stellar system is easily fathomed.

Also on the strength of photometric enumerations, Dr. Gould, of Boston, came to the conclusion, in 1879, that there is an extra thronging of stars about our sun, which forms one of a special group consisting of some four or five hundred members. The publication, in 1890, of the “Draper Catalogue,” of 10,530 photographed stellar spectra, has thrown fresh light on this interesting subject. Mr. Monck, of Dublin, gave reasons for holding stars physically like the sun to be generally nearer to us than stars of the Sirian class; and Professor Kapteyn, of Gröningen, as the result of a singularly able investigation, concluded with much probability that the sun belongs to a strongly condensed group of mostly “solar” stars, nearly concentric with the galaxy. It might, in fact, be said that we live in a globular cluster, since our native star-collection should appear from a very great distance under that distinctive form.

This modern quasi-discovery was anticipated by Herschel. He was avowedly indebted, it is true, to Michell’s “admirable idea” of the stars being divided into separate groups; but Michell did not trouble himself about the means of its possible verification, and Herschel did. He always looked round to see if there were not some touchstone of fact within reach.

His discussion of the solar cluster, though brief and incidental, is not without present interest. He found the federative arrangement of the stars to be “every day more confirmed by observation.” The “flying synods of worlds” formed by them must gravitate one towards another as if concentrated at their several centres of gravity. Accordingly, “a star, or sun, such as ours, may have a proper motion within its own system of stars, while the whole may have another proper motion totally different in quantity and direction.” We may thus, he continued, “arrive in process of time, at a knowledge of all the real, complicated motions of the planet we inhabit; of the solar system to which it belongs; and even of the sidereal system of which the sun may possibly be a member.” He proceeded to explain how stars, making part of the solar cluster, might be discriminated from those exterior to it; the former showing the perspective influence only of the sun’s translation among themselves, while the latter would be affected besides by a “still remoter parallax”—a secular drift, compounded of the proper motion of the sun within its cluster, and of its cluster relatively to other clusters.

The possibility of applying Herschel’s test is now fully recognised. Each fresh determination of the solar apex is scrutinised for symptoms of the higher “systematical parallax;” although as yet with dubious or negative results. Associated stellar groups are, nevertheless, met with in various parts of the sky. Herschel not only anticipated their existence, but suggested “a concurrence of proper motions” as the fittest means for identifying them.

His anticipation has been realised by Mr. Proctor’s detection of “star-drift.” Several stars in the Plough thus form a squadron sailing the same course; and similar combinations, on an apparently smaller scale, have been pieced together in various constellations. But the principle of their connection has yet to be discovered. They are evidently not self-centred systems; hence their companionship, however prolonged, must finally terminate. The only pronounced cluster with a common proper motion is the Pleiades; and its drift seems to be merely of a perspective nature—a reflection of the sun’s advance.

Bessel said of Herschel that “he aimed at acquiring knowledge, not of the motions, but of the constitution of the heavenly bodies, and of the structure of the sidereal edifice.” This, however, is a defective appreciation. He made, indeed, no meridian observations, and computed no planetary or cometary perturbations; yet if there ever was an astronomer who instinctively “looked before and after,” it was he. Could he have attained to a complete knowledge of the architecture of the heavens, as they stood at a given moment, it would not have satisfied him. To interpret the past and future by the present was his constant aim; from his “retired situation” on the earth, he watched with awe the grand procession of the sum of things defile through endless ages. He could not observe what was without at the same time seeking to divine what had been, and to forecast what was to come.

His nebular theory is now accepted almost as a matter of course. The spectroscope has lent it powerful support by proving the de facto existence of the “lucid medium,” postulated by him as a logical necessity. This was done August 1st, 1864, when Dr. Huggins derived from a planetary nebula in Draco a spectrum characteristic of a gaseous body, because consisting of bright lines. Their wave-lengths, which turned out to be identical for all objects of the kind, with one or two possible exceptions, indicated a composition out of hydrogen mixed with certain unfamiliar aeriform substances. Herschel’s visual discrimination of gaseous nebulæ was highly felicitous. Modern science agrees with him in pronouncing the Orion nebula, as well as others of the irregular class, planetaries, diffused nebulosities, and the “atmospheres” of “cloudy stars,” to be masses of “shining fluid.” As for his “ambiguous objects,” they remain ambiguous still. “Clusters in disguise” through enormous distance, give apparently the same quality of light with irresolvable nebulæ. His inference that stars and nebulæ form mixed systems has, moreover, been amply confirmed. No one now denies their significant affinity, and very few their genetic relationship.

Herschel gave a list in 1811 of fifty-two dim, indefinite nebulosities, covering in the aggregate 152 square degrees. “But this,” he added, “gives us by no means the real limits” of the luminous appearance; “while the depth corresponding to its superficial extent may be far beyond the reach of our telescopes;” so “that the abundance of nebulous matter diffused through such an expansion of the heavens must exceed all imagination.”

“The prophetic spirit of these remarks,” Professor Barnard comments, “is being every day made more evident through the revelations of photography.” He is himself one of the very few who have telescopically verified any part of these suggestive observations.

“I am familiar,” he wrote in Knowledge, January, 1892, “with a number of regions in the heavens where vast diffusions of nebulous matter are situated. One of these, in a singularly blank region, lies some five or six degrees north-west of Antares, and covers many square degrees. Another lies north of the Pleiades, between the cluster and the Milky Way; a portion of this has recently been successfully photographed by Dr. Archenhold. There is a large nebulous spot in that region, easily visible to the naked eye, which I have seen for many years. When sweeping there with a low power, the whole region between the Pleiades and the Milky Way is perceived to be nebulous. These great areas of nebulosity make their presence known by a singular dulling of the ordinarily black sky, as if a thin veil of dust intervened.” They “are specially suitable for the photographic plate, and it is only by such means that they can be at all satisfactorily located.”

Some of Herschel’s milky tracts have been thus pictured; notably one in the Swan, shown on Dr. Max Wolf’s plates to involve the bright star Gamma Cygni; and another immense formation extending over sixty square degrees about the belt and sword of Orion, and joining on, Herschel was “pretty sure,” to the great nebula. This, never unmistakably seen except by him, portrayed itself emphatically in 1886 in Professor E. C. Pickering’s photographs. Herschel’s persuasion of the subordinate character of the original “Fish-mouth nebula” was well-grounded. On plates exposed by Professors W. H. Pickering and Barnard, it is disclosed as the mere nucleus of a tremendous spiral, sweeping round from Bellatrix to Rigel.

Diffused nebulosities appear in photographs as far from homogeneous. They are not simple volumes of gas indefinitely expanding in all directions, after the manner of simple aeriform fluids. They possess, on the contrary, characteristic shapes. Structureless nebulæ, like structureless protoplasm, seem to be non-existent. In all, an organising principle is at work.

Minute telescopic stars showed to Herschel as prevalently red, owing, he conjectured, to the enfeeblement of their blue rays during an uncommonly long journey through space “not quite destitute of some very subtle medium.” The argument is a remarkable one. It would be valid if the ethereal vehicle of light exercised absorption after the manner of ordinary attenuated substances. There is, however, reason to suppose that the symptomatic redness was only a subjective impression, not an objective fact. His colour-sense was not quite normal. The lower, to his perception, somewhat overbalanced the higher end of the spectrum, and his mirrors added to the inequality by reflecting a diminished proportion of blue light. Thus he recorded many stars as tinged with red which are now colourless, yet lie under no suspicion of change.

Herschel was, in the highest and widest sense, the founder of sidereal astronomy. He organised the science and set it going; he laid down the principles of its future action; he accumulated materials for its generalisations, and gave examples of how best to employ them. His work was at once so stimulating and so practical that its abandonment might be called impossible. Others were sure to resume where he had left off. His son was his first and fittest successor; he was the only one who undertook in its entirety the inherited task. Yet there are to be found in every quarter of the world men imbued with William Herschel’s sublime ambitions. Success swells the ranks of an invading army; and the march of astronomy has, within the last decade, assumed a triumphal character. The victory can never be completely won; the march can never reach its final goal; but spoils are meanwhile gathered up by the wayside which eager recruits are crowding in to share. The heavens are, year by year, giving up secrets long and patiently watched for, while holding in reserve many others still more mysterious. There is no fear of interest being exhausted by disclosure.

Herschel’s dim intuition that something might be learned about the physical nature of the stars from the diverse quality of their light, was verified after sixty-five years, by the early researches of Secchi, Huggins, and Miller; but he could not suspect that, through the chemical properties, which he guessed to belong in varying degrees to the different sections of their spectra, pictures of the heavenly bodies would be obtained more perfect than the telescopic views he rapturously gazed at. Still less could he have imagined that, owing to its faculty of accumulating impressions too weak to affect the eye separately, the chemical would, in great measure, supersede the telescopic method in carrying out the designs he had most at heart.

Those designs have now grown to be of international importance. At eighteen northern and southern observatories a photographic review of the heavens is in progress. The combined results will be the registration, in place and magnitude, of fifteen to twenty millions of stars. The gauging of the skies will then be complete down to the fourteenth magnitude; and the “construction of the heavens” can be studied with materials of the best quality, and almost indefinite in quantity. By simply “counting the gauges” on Herschel’s early plan, much may be learnt; the amount of stellar condensation towards the plane of the Milky Way, for instance, and the extent of stellar denudation near its poles. A marked contrast between the measures of distribution in these opposite directions will most likely be brought into view. The application of his later method of enumeration by magnitudes ought to prove even more instructive, but may be very difficult. The obstacles, it is to be hoped, will not be insurmountable; yet they look just now formidable enough.

The grand problem with which Herschel grappled all his life involves more complicated relations than he was aware of. It might be compared to a fortress, the citadel of which can only be approached after innumerable outworks have been stormed. That one man, urged on by the exalted curiosity inspired by the contemplation of the heavens, attempted to carry it by a coup de main, and, having made no inconsiderable breach in its fortifications, withdrew from the assault, his “banner torn, but flying,” must always be remembered with amazement.

CAROLINE LUCRETIA HERSCHEL.

(From a portrait taken by Tielemann in 1829.)