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The Zodiacal Light

THE STORY OF
THE UNIVERSE

Told by Great Scientists
and Popular Authors

COLLECTED AND EDITED

By ESTHER SINGLETON

Author of “Turrets, Towers and Temples,” “Wonders of Nature,”
“The World’s Great Events,” “Famous Paintings,” Translator
of Lavignac’s “Music Dramas of Richard Wagner”

FULLY ILLUSTRATED

VOLUME I

THE
STARRY
SKIES

P. F. COLLIER AND SON

NEW YORK

Copyright 1905
By P. F. COLLIER & SON

PREFACE

In the following pages I have endeavored to present a comprehensive and general view of the material side of the universe. Instead of trying myself to tell the story of the universe, I have gone to the works of acknowledged weight and authority in this line of research and selected from them extracts of a popular character, especially those that are entertaining as well as merely instructive. The average reader is frequently repelled from the study of the sciences by the dry treatment adopted by those who try to instruct him. He cares little for laws, theories, or affinities; and he can not help being bored by attempts to make him understand classifications with their long lists of words manufactured from the names of modern celebrities or non-entities and roots from dead languages. I have therefore kept constantly in mind the person who seeks entertaining knowledge, and not the scientific specialist. I have tried to avoid all technicalities wherever possible.

Of late years, in fact ever since the foundation of the British Association, there has been a constantly increasing interest in the wonders of nature; and the specialist has responded to this popular interest in his scientific labors by speaking in language that an intelligent child can comprehend. People as a rule prefer to read of the habits, instincts, intelligence, and movements of animals and plants, rather than of their organs and structure. Thus the study of Natural History has received a great impetus from the writings of such men as Darwin and Lubbock; and Astronomy has been rendered more attractive to the lay reader by Flammarion, Gore, Proctor, and Ball. Every traveler who returns from remote or hitherto unknown Arctic or Torrid Zones has something fresh to tell us of the phenomena and life of our universe, which adds fresh stimulus to the popular interest in the Natural Sciences.

The Story of the Universe naturally falls under the following four heads:

First, the bodies moving in infinite space, including stars, dark and lucid, planets, nebulæ, comets, and meteors.

Second, the Earth, considered as a separate world and the only one of which we have precise detailed knowledge. In this chapter we learn of the past of our globe from the evidence afforded by the rocks of which its crust is composed. The varying conformations of its present surface are described, as is its atmospheric envelope and attendant phenomena. The ocean and its movements and depths are likewise fully considered.

Third, the Earth’s Garment—its flora. In this chapter we are told of the wonders and beauties of plant-life, its development and distribution.

Fourth, the Earth’s Creatures. Here we have a general view of animal life, from the mighty mammoth to the fairy fly: even the beings visible only to the microscope are not forgotten. Special attention is also paid to man, from his origin to the present day.

I have made the selections from authentic editions of the writings of the scientists; and have taken no liberties with the text, with the exception of occasional cutting.

In the Introduction I have given a short sketch of the development of the Natural Sciences, from the dawn of written history to the present day.

E. S.

New York, March, 1905.

INTRODUCTION

The knowledge of the Natural Sciences among the Greeks and Romans was derived principally from the Egyptians and Babylonians. The Phœnicians in their voyages, also, necessarily paid considerable attention to Astronomy. Their Cynosura consisted of the tail of the Little Bear, by which they steered. The great names in Greek Astronomy are Aratus, Hipparchus, and Ptolemy.

From the fancies of Astrology, in which the early Arabs largely indulged, and which, though discountenanced by Mahomet himself, have never been wholly abandoned by their descendants, a not unnatural transition, led to the study of Astronomy. Under the patronage of the Abbaside Caliph Al-Mamun (813-833 A. D.) this science made rapid progress.

Astronomy was zealously studied in the famous schools of Bagdad and Cordova.

The Almagest, or System of Astronomy, by Ptolemy, was translated into Arabic by Alhazi and Sergius as early as 812. In the Tenth Century, Albaten observed the advance of the line of the apsides in the earth’s orbit; Mohammed-ben-Jeber-al-Batani, the obliquity of the ecliptic; Alpetragius wrote a theory of the planets; and Abul-Hassan-Ali, on astronomical instruments. The obliquity of the ecliptic, the diameter of the earth, and even the precession of the equinoxes, were then calculated with commendable accuracy; and shortly after, Abul-Mezar’s Introduction to Astronomy and his Treatise on the Conjunction of the Planets, with the Elements of Al-Furjanee (though this last author was largely indebted to the Egyptian labors of Ptolemy), proved that the caliph’s liberality had been well bestowed. But Al-Batinee, a native of Syria (879-920 A. D.), surpassed all his predecessors in the nicety alike of his observations and computations. Geber, at Seville, constructed (1196 A. D.) the first astronomical observatory on record; and Ebn-Korrah in Egypt proved by his example that the Arabs could be even better astronomers than the Greeks.

Ulug Bekh, grandson of the great Tamerlane, was a diligent observer. He established an academy of astronomers at Samarcand, the capital of his dominions, and constructed magnificent instruments. Ulug Bekh, too, made a catalogue of the fixed stars—the only one that had been compiled since that of Hipparchus, sixteen centuries previously.

Gradually, by their intercourse with civilized nations, the Arabian conquerors were themselves subjected to the humanizing influence of letters, and, after 749 A. D., or during the reign of the Abassides, literature, arts, and sciences appeared, and were generously fostered under the splendid sway, first of Almansor (754-775), and afterward of the celebrated Harun-al-Raschid (786-808). Learned men were now invited from many countries and remunerated for their labors with princely munificence; the works of the best Greek, Syriac, and old Persian writers were translated into Arabic, and spread abroad in numerous copies. The Caliph Al-Mamun, who reigned from 813 to 833, offered to the Greek emperor five tons of gold and a perpetual treaty of peace on condition that the philosopher Leo should be allowed to give instruction to the former. Under the same Caliph the famous schools of Bagdad, Basra, Bokhara, and Kufa were founded, and large libraries were collected in Alexandria, Cairo, and Bagdad. The school of Cordova in Spain soon rivaled that of Bagdad, and in the Tenth Century the Arabs were everywhere the preservers and distributers of knowledge.

Pupils from France and other European countries repaired to Spain in great numbers, to study mathematics and medicine under the Arabs. There were fourteen academies, with many preparatory and upper schools, in Spain, and five very considerable public libraries; that of the Caliph Hakem containing, as is said, more than 600,000 volumes.

In Geography, History, Philosophy, Medicine, Physics, and Mathematics the Arabians rendered important services to science; and the Arabic words still employed in science—such as algebra, alcohol, azimuth, zenith, nadir, with many names of stars, etc. (see The Arabian Heavens, pages 106-120 of Vol. I)—remain as indications of their influence on the early intellectual culture of Europe. But Geography owes most to them during the Middle Ages. In Africa and Asia, the boundaries of geographical science were extended, and the old Arab treatises on geography and works of travels in several countries by Abulfeda, Edrisi, Leo Africanus, Ibn Batuta, Ibn Foslan, Ibn Jobair, Albiruni the astronomer, and others, are still interesting.

The structure of the earth received little attention from the ancients; the extent of its surface known was limited, and the changes upon it were neither so speedy nor violent as to excite special attention. The only opinions deserving to be noticed are those of Pythagoras and Strabo, both of whom observed the phenomena which were then altering the surface of the earth, and proposed theories for explaining the changes that had taken place in geological time. The first held that, in addition to volcanic action, the change in the level of sea and land was owing to the retiring of the sea; while the other maintained that the land changed its level, and not the sea, and that such changes happened more easily to the land below the sea because of its humidity.

From the fall of the Roman empire, during the Dark Ages, the physical sciences were neglected. In the Tenth Century, Avicenna, Omar, and other Arabian writers commented on the works of the Romans, but added little of their own.

Geological phenomena attracted attention in Italy in the Sixteenth Century, the absorbing question then being as to the nature of fossils; only a few maintained that they were the remains of animals. Two centuries elapsed before the opinion was generally adopted.

Aristotle was the first who collected, in his work On Meteors, the current prognostics of the weather. Some of these were derived from the Egyptians, who had studied the science as a branch of Astronomy, while a considerable number were the result of his own observation. The next writer upon this subject was Theophrastus, one of Aristotle’s pupils, who classified the opinions commonly received regarding the weather under four heads, viz., the prognostics of rain, of wind, of storm, and of fine weather. The subject was discussed purely in its popular and practical bearings, and no attempt was made to explain phenomena whose occurrence appeared so irregular and capricious. Cicero, Virgil, and a few other writers also wrote on the subject; but the treatise of Theophrastus contains nearly all that was known down to comparatively recent times. Partial explanations were attempted by Aristotle and Lucretius, but their explanations were vague, and often absurd.

In this dormant condition meteorology remained for ages, and no progress was made till proper instruments were invented for making real observations with regard to the temperature, the pressure, the humidity, and the electricity of the air.

Solomon spoke of “trees, from the cedar in Lebanon even to the hyssop that springeth out of the wall.” There is reason also to believe that Zoroaster devoted some attention to plants, and that this study early engaged some of the philosophers of Greece. The oldest botanical work which has come down to us is that of Theophrastus, the pupil of Aristotle, who flourished in the fourth century B. C. His descriptions of plants are very unsatisfactory, but his knowledge of their organs and of vegetable physiology may well be deemed wonderful. It was not, indeed, till after the revival of letters in Western Europe, that it was ever again studied as it had been by him. About four hundred years after Theophrastus, in the First Century of the Christian era, Dioscorides of Anazarbus, in Asia Minor—a herbalist, however, rather than a botanist—described more than 600 plants in a work which continued in great repute throughout the Middle Ages.

About the same time, the elder Pliny devoted a share of his attention to Botany, and his writings contain some account of more than 1,000 species, compiled from various sources and mingled with many errors. Centuries elapsed without producing another name worthy to be mentioned. It was among the Arabians that the science next began to be cultivated, about the close of the Eighth Century. The greatest name of this period is Avicenna. Among the Arabs, Botany, like Chemistry, was chiefly studied as subsidiary to medicine; but as an adjunct to the old herbal pharmacopœia, it received close attention. The principal mercurial and arsenical preparations of the materia medica, the sulphates of several metals, the properties of acids and alkalies, the distillation of alcohol—in fine, whatever resources chemistry availed itself of up to a very recent date—were, with their practical application, known to Er-Razi and Geber. In fact, the numerous terms borrowed from the Arabic language—for instance, alcohol, alkali, alembic, and others—with the signs of drugs and the like, still in use among modern apothecaries, remain to show how deeply this science is indebted to Arab research.

Aristotle seems to have been the first to study Zoology. Some of the groups he established still retain their place in the most modern classifications. His two great sections of the Animal Kingdom consisted of Enanima (red blood) and Anima (having a circulation of colorless fluid). Ælian and Pliny wrote on the subject, but they indulged largely in fables. There was little advance in the science during the Dark and Middle Ages. The Bestiaries were written for the sake of moral teaching, and the animals had to behave with that end in view. Albertus Magnus is the only famous name in this department before the revival of learning.

The shining light of the Thirteenth Century was Roger Bacon. His Opus Majus is “at once the Encyclopædia and the Novum Organum of the Thirteenth Century.” In this, besides other branches of scientific research, he devotes a rapid examination to questions of Climate, Hydrography, Geography, and Astrology. Scientific research, however, was out of date, and from the educated world Roger Bacon received small recognition. His writings earned only a prison from his own Order, and he died, in his own words, “unheard, forgotten, buried.”

The Revival of Learning, commonly known as the Period of the Renaissance, naturally entailed renewed interest in the sciences as well as the arts. Green gives a comprehensive view of it:

“The last royalist had only just laid down his arms when the little company who were at a later time to be known as the Royal Society gathered round Wilkins at Oxford. It is in this group of scientific observers that we catch the secret of the coming generation. From the vexed problems, political and religious, with which it had so long wrestled in vain, England turned at last to the physical world around it, to the observation of its phenomena, to the discovery of the laws which govern them. The pursuit of physical science became a passion; and its method of research, by observation, comparison, and experiment, transformed the older methods of inquiry in matters without its pale. In religion, in politics, in the study of man and of nature, not faith but reason, not tradition but inquiry, were to be the watchwords of the coming time. The dead-weight of the past was suddenly rolled away, and the new England heard at last and understood the call of Francis Bacon.

“Bacon had already called men with a trumpet-voice to such studies; but in England at least Bacon stood before his age. The beginnings of physical science were more slow and timid there than in any country of Europe. Only two discoveries of any real value came from English research before the Restoration; the first, Gilbert’s discovery of terrestrial magnetism in the close of Elizabeth’s reign; the next, the great discovery of the circulation of the blood, which was taught by Harvey in the reign of James. Apart from these illustrious names England took little share in the scientific movement of the continent; and her whole energies seemed to be whirled into the vortex of theology and politics by the Civil War. But the war had not reached its end when a little group of students were to be seen in London, men ‘inquisitive,’ says one of them, ‘into natural philosophy and other parts of human learning, and particularly of what hath been called the New Philosophy,... which from the times of Galileo at Florence, and Sir Francis Bacon (Lord Verulam) in England, hath been much cultivated in Italy, France, Germany, and other parts abroad, as well as with us in England.’ The strife of the time indeed aided in directing the minds of men to natural inquiries. ‘To have been always tossing about some theological question,’ says the first historian of the Royal Society, Bishop Sprat, ‘would have been to have made that their private diversion, the excess of which they disliked in the public. To have been eternally musing on civil business and the distresses of the country was too melancholy a reflection. It was nature alone which could pleasantly entertain them in that estate.’ Foremost in the group stood Doctors Wallis and Wilkins, whose removal to Oxford, which had just been reorganized by the Puritan Visitors, divided the little company into two societies. The Oxford society, which was the more important of the two, held its meetings at the lodgings of Dr. Wilkins, who had become Warden of Wadham College, and added to the names of its members that of the eminent mathematician Dr. Ward, and that of the first of English economists, Sir William Petty. ‘Our business,’ Wallis tells us, ‘was (precluding matters of theology and state affairs) to discourse and consider of philosophical inquiries and such as related thereunto, as Physick, Anatomy, Geometry, Astronomy, Navigation, Statics, Magnetics, Chymicks, Mechanicks, and Natural Experiments: with the state of these studies, as then cultivated at home and abroad. We then discoursed of the circulation of the blood, the valves in the venæ lacteæ, the lymphatic vessels, the Copernican hypothesis, the nature of comets and new stars, the satellites of Jupiter, the oval shape of Saturn, the spots in the sun and its turning on its own axis, the inequalities and selenography of the moon, the several phases of Venus and Mercury, the improvement of telescopes, the grinding of glasses for that purpose, the weight of air, the possibility or impossibility of vacuities, and Nature’s abhorrence thereof, the Torricellian experiment in quicksilver, the descent of heavy bodies and the degree of acceleration therein, and divers other things of like nature.’

“The other little company of inquirers, who remained in London, was at last broken up by the troubles of the Second Protectorate; but it was revived at the Restoration by the return to London of the more eminent members of the Oxford group. Science suddenly became the fashion of the day. Charles was himself a fair chymist, and took a keen interest in the problems of navigation. The Duke of Buckingham varied his freaks of riming, drinking, and fiddling by fits of devotion to his laboratory. Poets like Dryden and Cowley, courtiers like Sir Robert Murray and Sir Kenelm Digby joined the scientific company to which in token of his sympathy with it the King gave the title of ‘The Royal Society.’ The curious glass toys called Prince Rupert’s drops recall the scientific inquiries which, with the study of etching, amused the old age of the great cavalry leader of the Civil War. Wits and fops crowded to the meetings of the new society. Statesmen like Lord Somers felt honored at being chosen its presidents. Its definite establishment marks the opening of a great age of scientific discovery in England. Almost every year of the half century which followed saw some step made to a wider and truer knowledge. Our first national observatory rose at Greenwich, and modern astronomy began with the long series of astronomical observations which immortalized the name of Flamsteed. His successor, Halley, undertook the investigation of the tides, of comets, and of terrestrial magnetism. Hooke improved the microscope, and gave a fresh impulse to microscopical research. Boyle made the air-pump a means of advancing the science of pneumatics, and became the founder of experimental chymistry. Wilkins pointed forward to the science of philology in his scheme of a universal language. Sydenham introduced a careful observation of nature and facts which changed the whole face of medicine. The physiological researches of Willis first threw light upon the structure of the brain. Woodward was the founder of mineralogy. In his edition of Willoughby’s Ornithology, and in his own History of Fishes, John Ray was the first to raise zoology to the rank of a science; and the first scientific classification of animals was attempted in his Synopsis of Quadrupeds. Modern botany began with his History of Plants, and the researches of an Oxford professor, Robert Morison; while Grew divided with Malpighi the credit of founding the study of vegetable physiology. But great as some of these names undoubtedly are, they are lost in the lustre of Isaac Newton. Newton was born at Woolsthorpe in Lincolnshire, on Christmas Day, in the memorable year which saw the outbreak of the Civil War. In the year of the Restoration he entered Cambridge, where the teaching of Isaac Barrow quickened his genius for mathematics, and where the method of Descartes had superseded the older modes of study. From the close of his Cambridge career his life became a series of great physical discoveries. At twenty-three he facilitated the calculation of planetary movements by his theory of Fluxions. The optical discoveries to which he was led by his experiments with the prism, and which he partly disclosed in the lectures which he delivered as mathematical professor at Cambridge, were embodied in the theory of light which he laid before the Royal Society on becoming a Fellow of it. His discovery of the law of gravitation had been made as early as 1666; but the erroneous estimate which was then generally received of the earth’s diameter prevented him from disclosing it for sixteen years; and it was not till the eve of the Revolution that the Principia revealed to the world his new theory of the Universe.”

Ever since the Fifteenth Century, when Copernicus revived the ancient theory of Pythagoras that the planets revolved around the sun (a theory left in an imperfect state and demonstrated later by Kepler, Galileo, Newton, and others) astronomical research has progressed steadily. It must be remembered, however, that De Revolutionibus Orbium, which met with great opposition, contained nothing regarding the laws of motion, for these had not been as yet discovered, and Saturn marked the boundaries of the Solar System. Copernicus assigned the “fixed stars” to a sphere, as in Ptolemy’s heavens (see [page 331]).

The great Danish astronomer, Tycho Brahe, whose idea of the Solar System is represented on [page 343], was his opponent. Brahe, however, a devoted student, a man of wealth, the favorite of kings and princes, and the proud possessor of the Castle of Uraniberg (City of the Heavens), an observatory equipped with fine instruments and built for him by Frederick II, King of Denmark, on the island of Hueen, and after his death the protégé of Rudolph II at Benatek, near Prague, contributed greatly to the advancement of the science by means of his discoveries, computations, solar and lunar tables, and catalogue of stars. He, like Copernicus, placed the “fixed stars” in an outer sphere. His observations on the planets were made to prove the truth of his system. This mass of observations was used instead by Johann Kepler, who had been his assistant at the Benatek Observatory, to prove Copernicus’s theory. Of Kepler, the discoverer of the three famous laws, who gave a complete theory of solar eclipses, calculated the transits of Mercury and Venus, and made numerous discoveries in optics and general physics, Proctor says:

“Kepler was not merely an observer and calculator; he inquired with great diligence into the physical causes of every phenomenon, and made a near approach to the discovery of that great principle which maintains and regulates the planetary motions. He possessed some very sound and accurate notions of the nature of gravity, but unfortunately conceived it to diminish simply in proportion to the distance, although he had demonstrated that the intensity of light is reciprocally proportional to the surface over which it is spread, or inversely as the square of the distance from the luminous body.”

Great names follow in rapid succession. One of Kepler’s contemporaries was Galileo Galilei, the discoverer of the “three laws of motion” and the relation of time and space in falling bodies, the first to apply the newly invented telescope to the observation of the heavens and the discoverer of four satellites of Jupiter (named by him the “Medeiran Stars” in honor of his patron). He also detected spots on the sun’s disk, the phases of Venus, and irregularities on the moon’s surface, and declared the Milky Way to be composed of a countless tract of separate stars.

When we remember the limited power of the telescope of the age, we can but marvel, not at how little, but how much was known regarding the starry skies.

During this period, numerous observers rendered great service to Astronomy, and other scientists were engaged in making useful drawings, charts, maps, tables, and catalogues of stars.

To this period also belongs John Bayer of Augsburg, who published a description of the constellations with maps upon which the stars were marked with the letters of the Greek Alphabet—a convenient method that was universally adopted and is still in use. Other names include Gassendi, Riccioli, Grimaldi, and Hevelius—the latter a rich citizen of Dantzig, who had a fine observatory of his own, where he worked for forty years. His drawings and descriptions of the moon, his researches on comets, which he still believed moved in parabolas, and his celestial charts engaged most of his attention.

The Dutch astronomer Huygens (born in 1629) is famous for his improvements in the telescope use of the pendulum clock and developments in the machinery of astronomical instruments. He discovered the ring of Saturn and four of his satellites. Edmund Halley, an English astronomer (born in 1656), also took a great interest in the telescope, and went to Dantzig to settle a controversy between Robert Hooke and Hevelius regarding the best glasses for use in astronomical observations; for Hevelius still worked with the ancient instruments, while Hooke believed in the lens.

Halley revived the ancient idea that comets belonged to the Solar System, and predicted that the comet of 1681 would return to its perihelion in 1759. This was the first prediction of its kind verified.

During the last quarter of the Seventeenth Century, the telescope assumes importance and two great observatories begin their work. In 1670 the Paris Observatory, of which Cassini was made director, was finished, and five years later the Greenwich Observatory, where Flamsteed was installed as royal astronomer.

Of Cassini, Lalande remarks that under him Astronomy underwent revolutions, and in France he was regarded as the “creator of the science.” Cassini discovered that Saturn’s ring was double and found four satellites of Jupiter.

Flamsteed’s observations on planets, satellites, comets, “fixed stars,” and his catalogue of 2,884 stars were valuable contributions to science; and his Historia Cœlestis is said to have “formed a new era in sidereal astronomy.”

Flamsteed was succeeded by Halley, particularly famed for his investigations of comets. The next great astronomical event was the discovery of Uranus by Sir William Herschel in 1781. Sir William Herschel also discovered two more of Saturn’s satellites, and began the great work of resolving the Milky Way and other clusters into swarms of suns, single stars into double and triple stars, inquiries into the mysteries of the nebulæ, and in every way enlarging the general conception of the sidereal universe.

To the end of the Eighteenth and beginning of the Nineteenth Centuries belongs the brilliant French astronomer and mathematician Laplace, who published in 1799-1808 his Mécanique Céleste, in which he announced his Nebular Hypothesis (described on page 433 of Vol. II. The discoveries of the Planetoids are described on [pages 396-403], and that of Neptune in 1846 on [pages 430-432]). The latest important additions to the Solar System are the discovery by Prof. Barnard of Jupiter’s Fifth Satellite in 1892 and Saturn’s Ninth by Prof. W. H. Pickering in 1904. The discovery even of a Seventh Satellite of Jupiter has just been announced from the Lick Observatory.

It would be impossible to mention the names of the astronomers whose work from the middle of the last century to its closing years has been distinguished in various fields. Space only permits brief mention of the new methods of research by means of the spectroscope and celestial photography. With the first the name of the English astronomer, William Huggins, is identified and has yielded most important and startling information regarding the composition of heavenly bodies, and with the application of the photographic telescope these new methods have created a revolution in astronomical observation.

It may be interesting to gain a slight idea of the numbers of stars revealed by the camera by referring to Sir Robert Ball:

“If we take a position on the equator, from whence, of course, all the heavens can be completely seen in the lapse of six months, the number of stars that can be reckoned with the unaided eye will, according to Houzeau, amount to about six thousand. If we augment our unaided vision by a telescope of even small dimensions, such as three inches in diameter, the number of stars in the Northern Hemisphere alone is upward of three hundred thousand. We may assume that the Southern Hemisphere has an equally numerous star-population, so that the entire multitude visible with this optical aid is about six hundred thousand. Thus we see that the use of a telescope small enough to be carried in the hands suffices to multiply the lucid stars one-hundredfold. Great telescopes no doubt soon show us that the hundreds of thousands are only the brighter members of a host of millions, and now we receive the assurance of photography that the telescopic stars are only the more conspicuous members of that vast universe. Mr. Roberts indeed declares that the multitudes of stars on the photographic plate grow with each increase of exposure to such a degree that it would almost seem as if the plate would be a wellnigh continuous mass of stars if the operations could be sufficiently protracted.”

Naturally the past years have witnessed the making of new catalogues and maps of stars, and many valuable computations of parallaxes, etc. Some of the results obtained by these new methods are described in the chapters on the Nebulæ and Swarms of Suns, The Great Nebula of Orion, and The Colored, Double, Multiple, Binary, Variable, and Temporary Stars in Vol. I. From this brief survey of the progress of Astronomy the fact will be appreciated, therefore, that all the discoveries and researches have resulted in a larger conception of the universe, and the Solar System sinks into insignificance in the vast ocean of stars and suns.

The study of the Earth’s crust and its contents divested of superstition dates from the end of the Seventeenth Century. Nicolaus Steno (1638-1687), a Dane, devoted himself to geology, and in 1669 observed successive layers of strata. He is called “the father of Palæontology.” In 1680 Leibnitz proposed the theory that the Earth was originally in a molten state. The classification of strata was begun about the middle of the Eighteenth Century. The views of James Hutton (1788), who returned to the theories advanced by Ray (a return to the views of Pythagoras), were continued by Sir Charles Lyell.

Geology and Palæontology have progressed side by side. Among the most famous investigators are Cuvier, Dawson, Marsh, Owen, Huxley, Agassiz, De Blainville, Kaup, Sir Roderick Murchison, Boyd Dawkins, Sir William Flower, R. Lydekker, and E. D. Cope.

To the review of the new developments of meteorology and the science of probabilities by Sir Ralph Abercromby, on pages 784-792 of Vol. II, it is only necessary to add that the interest in meteorological research developed greatly after Torricelli’s discovery in 1643 of weight and pressure in the atmosphere led to the perfection of the barometer and the development of the thermometer and hygrometer, both in the Seventeenth Century. The theory of trade-winds George Hadley announced in the Philosophical Transactions for 1735. Dalton’s Meteorological Essays, published in 1793, and Dr. William Charles Wells’s Theory of Dew, published in 1814, attracted much attention. Regarding the inquiries into the laws of light by Snell, Newton, Descartes, Thomas Young, and Sir George Airy, the reader is referred to the chapter on The Rainbow in Vol. II, by John Tyndall, with whose researches in the latter half of the Nineteenth Century every one is more or less acquainted.

Little need be said here regarding the history of Botany, which is reviewed on pages 984-1000 of Vol. II. We may add, however, that one of the first to revive this study was Otto Brunsfels, whose Historia Plantarum Argentorati was published in two folio volumes with cuts in Strasburg in 1530. He had many followers on the Continent and in England. During the revival of learning, chairs of Botany were founded in the universities; botanic gardens were established in many places (the Jardin des Plantes was founded in 1626); and botanists began to travel to remote countries to search for unknown flora.

To the Seventeenth Century belong the names of Dr. Turner, “the father of English Botany”; Robert Morison, professor of Botany at Oxford; John Ray, Nehemiah Grew, Malpighi, Henshaw, and Robert Hooke. The two latter were among the first to employ the newly invented microscope to the study of this science. It may be mentioned in passing, that Huygens is said to have taken from Holland to England microscopes about the size of a grain of sand, and that the first microscope consisting of a combination of lenses is attributed to Jansen, a spectacle-maker of Holland. Hooke, whom Herschel calls “the great contemporary and almost the rival of Newton,” gave a tremendous impetus to Microscopy, and practically laid the foundation of Histology or the Inner Morphology of Plants, due to Grew and Malpighi. Schleiden undertook to explain the mysteries of cell formation in 1838, further investigated by Schwann, and is now known as the Schleiden-Schwann theory. Nägeli and Von Mohl continued researches on this line. To the contents of the cell Von Mohl gave the name protoplasm.

In 1849, Hofmeister began investigations into the life-histories of plants, since when the study of Vegetable Physiology has progressed side by side with Chemistry. To Darwin great subjects are due: the cross-fertilization of plants, their reproduction, and their relations to insects and their movements. It may be mentioned, however, that in 1693 Ray attempted to explain the movements of leaves, tendrils, and petals by physical and mechanical laws.

Since the middle of the Nineteenth Century, the branches of Botany that have been particularly studied are Vegetable Physiology and Pathology, Inner Morphology, and Fossil Botany—and the discoveries made have naturally had an effect upon the classification of vegetable life.

According to Agassiz:

“We must come down to the last century, to Linnæus, before we find the history taken up where Aristotle had left it, and some of his suggestions carried out with new freshness and vigor. Aristotle had already distinguished between genera and species; Linnæus took hold of this idea, and gave special names to other groups, of different weight and value. Besides species and genera, he gives us orders and classes—considering classes the most comprehensive, then orders, then genera, then species. He did not, however, represent these groups as distinguished by their nature, but only by their range; they were still to him, as genera and species had been to Aristotle, only larger or smaller groups, not founded upon and limited by different categories of structure. He divided the animal kingdom into six classes: Mammalia, Birds, Reptiles, Fishes, Insects, and Worms.”

Linnæus’s classification was, therefore, the first attempt to group animals; but until Cuvier there was no great principle of classification. In 1707 Buffon succeeded in making Zoology, which had been regarded as a most uninteresting study, popular and respected. He also had the idea of collecting all the known facts of scientific investigation and arranging them systematically. Buffon was ridiculed as a scientist by his contemporaries, Hevelius, Diderot, D’Alembert, and Condillac, who opposed his explanations of natural phenomena. Buffon’s Histoire Naturelle Générale et Particulière is his most important work. A complete edition in thirty-six volumes appeared in Paris in 1749-1788. Although it is said to “have made an epoch in the study of the natural sciences” in Buffon’s day, it now possesses little scientific value.

Cuvier’s classification has never been overthrown. His original investigations in various departments of science, and particularly that of fossil vertebrate animals, opened up new fields of study. His talents with both pen and pencil contributed largely to making that branch of science popular.

Lamarck, Cuvier’s contemporary, divided the animal kingdom into Vertebrates and Invertebrates. Lamarck, like Geoffroy Saint-Hilaire, was a believer in the theory of evolution, which was opposed by Cuvier.

Lamarck turned from the study of Meteorology to that of Botany, and later again to that of Zoology. In 1793 he became professor of the natural history of the lower classes of animals in the Jardin des Plantes. His theories have greatly influenced modern science, particularly that of the “Variation of Species,” which was set forth in his Philosophie Zoologique (two vols., Paris, 1809) and other works. Lamarck’s Histoire des Animaux sans Vertèbres (seven vols., Paris, 1815-22) is his greatest work.

Karl Ernst von Baer, the Russian naturalist, a pupil of Döllinger in Würzburg, devoted himself chiefly to the study of embryology and made valuable discoveries.

Passing by many illustrious names, we come to that of Sir Richard Owen, of whom it has been said that “from the sponge to man, he has thrown light over every subject he has touched.” His work in the Hunter Museum, his descriptions and restorations of extinct birds and animals, and his original works on every branch of animal life, form an enormous contribution to the progress of science. He promulgated the advanced views of John Hunter, the great physiologist and surgeon, of whose famous museum of more than ten thousand specimens, illustrative of anatomy and natural history, he became curator.

Three names shine with especial lustre upon the Nineteenth Century—Darwin, Huxley, and Spencer. The theory of evolution first appeared in De Maillet’s work, Telliamed, published in 1758, but written in 1735. More than thirty writers before Darwin treated this theory, among whom were Erasmus Darwin, Goethe, Lamarck, and Geoffroy Saint-Hilaire. Largely owing to the opposition of Cuvier, it never succeeded until it was revived by Charles Darwin, who, after twenty-one years of work, published his results in 1858 in the Journal of the Linnæan Society, followed in the next year by The Origin of Species by Means of Natural Selection (see pages 1482-1512 of Vol. IV).

“The lifeless earth,” says Sir Robert Ball, “is the canvas on which has been drawn the noblest picture that modern science has produced. It is Darwin who has drawn this picture. He has shown that the evolution of the lifeless earth from the nebula is but the prelude to an organic evolution of still greater interest and complexity. He has taken up the history of the earth at the point where the astronomer left it, and he has made discoveries which have influenced thought and opinion more than any other discoveries that have been made for centuries.”

The neglected department of Marine Zoology the Nineteenth Century has made particularly its mission to investigate, but space only permits mention of four names: Edward Forbes, Lord Kelvin (Sir Wyville Thomson), Ernst Heinrich Haeckel, and the Prince of Monaco.

The first, whom Lord Kelvin considers “the most accomplished and original naturalist of his time,” was a pupil of Geoffroy Saint-Hilaire, Jussieu, and De Blainville. He is regarded as the originator of the use of the dredge for collecting specimens and the first who undertook the systematic study of Marine Zoology with reference to the distribution of fauna. In 1859 his Natural History of the European Seas appeared after his death.

One of the most important investigators in this line is Prof. Haeckel, famous for his studies of the lower class of marine animals. He is also distinguished for his researches in other branches of Zoology and Palæontology, and was one of the first followers of Darwin in Germany.

Entomology has also made enormous progress during the Nineteenth Century. At the end of the Seventeenth Century, Ray estimated the number of insects throughout the world at 10,000 species! The great entomologists of the Eighteenth Century include Linnæus, De Geer, and Fabricius. Next follow Latreille, Kirby and Spence, and a host of distinguished scientists in Europe and the United States, of whom Sir John Lubbock (Lord Avebury) heads the list. A comparatively new line of investigation is that of the Chalcididæ (see Fairy Flies, pages 1449-1458, in Vol. IV).

ESTHER SINGLETON.

ILLUSTRATIONS

CONTENTS

THE

STORY OF THE UNIVERSE

THE HEAVENS.—Amédée Guillemin

What are the heavens? Where the shores of that limitless ocean; where the bottom of that unfathomable abyss?

What are those brilliant points—those innumerable stars, which, never dim, shine out unceasingly from the dark profound? Are they sown broadcast—orderless, with no other bond save that which perspective lends to them? Or, if not immovable, as we have so long imagined, if not golden nails fixed to a crystal vault, whither are they bound? And, finally, what are the parts assigned to the sun, our earth, and all the earths attendant on the glorious orb of day in this tremendous concert of celestial spheres—this sublime harmony of the universe?

These are magnificent problems of which the most fertile imagination would have in vain attempted the solution, if, for the greater glory of the human mind, astronomy—first born of the sciences—had not at length come to our aid.

How wonderful is the power of man! Chained down to the surface of the earth, an intelligent atom on a grain of sand lost in the immensity of a space, he invents instruments which multiply a thousand-fold his vision, he sounds the depths of the ether, gauges the visible universe, and counts the myriads of stars which people it; next, studying their most complicated movements, he measures exactly their dimensions and the distances of the nearest of them from the earth, and next deduces their masses; then, discovering in the seeming disorder of the stellar groupings real bonds of union, he at last evolves order from apparent confusion.

Nor is this all. Rising by a supreme flight of thought to the most abstract speculations, he discovers the laws which regulate all celestial movements, and defines the nature of the universal force which sustains the worlds.

Such are the fruits of the unceasing labors of twenty generations of astronomers. Such the result of the genius and of the patient perseverance of men who have devoted themselves for two thousand years to the study of the phenomena of the heavens. The Chaldean shepherds were, they say, the first astronomers. We can well believe it. Dwelling in the midst of vast plains, where the mildness of the seasons permitted them to pass the night in the open air, where the clear sky unfolded before them perpetually the most glorious scenes, they ought to have been, and they were, contemplative astronomers. And all of us would be what they were did not the rigor of our climate and our variable atmosphere so often prevent us observing the heavens; and did not, moreover, the turmoil and cares of civilized life deprive us of the necessary leisure.

Nothing is more fitted to elevate the mind toward the infinite than the pensive contemplation of the starry vault in the silent calm of night. A thousand fires sparkle in all parts of the sombre azure of the sky. Varied in color and brilliancy, some shine with a vivid light, perpetually changing and twinkling; others, again, with a more constant one—more tranquil and soft; while very many only send us their rays intermittently, as if they could scarce pierce the profundity of space.

To enjoy this spectacle in all its magnificence, a night must be chosen when the atmosphere is perfectly pure and transparent—one neither illuminated by the moon, nor by the glimmer of twilight or of dawn. The heavens then resemble an immense sea, the broad expanse of which glitters with gold dust or diamonds.

In presence of such splendor, the senses, mind and imagination are alike inthralled. The impression gathered is an emotion at once profound and religious, an indefinable mixture of admiration, and of calm and tender melancholy. It seems as if these distant worlds, in shining earthward, put themselves in close communication with our thoughts.

At a first glance at the starry firmament the stars seem pretty regularly distributed; nevertheless, look at that whitish, undecided, vapory glimmer which girdles the heavens as with a belt. It is the Milky Way.[1] As we approach the borders of this star-cloud in our inspection, the stars appear more and more crowded together, and most of them so small that the eye can scarcely distinguish them. The accumulation of stars in the direction of the Milky Way is more especially visible when we examine the heavens with the aid of a powerful telescope.

The Milky Way itself is nothing more than an immensely extended zone of stars, that is, of suns, since each star, from the most brilliant to the faintest, is a sun.

Here, then, is an immense group, a gigantic assemblage of worlds, which seems to embrace all the universe, if it be true that the greater number of the scattered stars situated out of the Milky Way nevertheless form part of it. In reality, this multitude of millions of suns is divided into numerous and distinct groups, and those into others still more restricted in number, each composed of two or three suns.

What breadth of space does each of these groups occupy? What is the measure of the space which holds them all? The most powerful imagination in vain attempts to answer these questions intelligibly; here numbers fail us.

Let us add—a fact well proved, and one which will seem strange to many—

Our sun himself is a star of the Milky Way.

In examining attentively every part of the starry vault, a keen eye perceives here and there whitish spots resembling little clouds. One would say they were so many patches detached from the Milky Way, from which, however, they are often very distinct and very distant. The telescope discovers by thousands those cloud-patches, these—to give them their astronomical name—Nebulæ.

It was formerly imagined that each of these star-clouds was nothing more than an accumulation of stars, very close together, and very numerous—so many Milky Ways lying outside our own, and for the most part so distant that the most powerful instruments were able only to distinguish a confused glimmering. One of the most important observations of modern times, however, has shown that many of these nebulæ, including the most glorious one in our northern hemisphere—that in the sword-handle of Orion—are but masses of glowing gases.

Others, again, of these cloud-like masses—cloud-like by reason of their distance—show us, faintly shining on a background of apparent nebulæ, brilliant stars, larger no doubt, or more brilliant, than their fellows, and some of these objects called “Star-Clusters,” which are nearest to us, are among the most glorious objects revealed to us by our telescopes.

Let us attempt now to conceive what fearful distances separate these archipelagoes of worlds from our own!

Unfathomable abysses whose unspeakable depths the most powerful telescopes increase indefinitely! Profound, endless, bottomless, but lighted up by millions of suns!

Such appears to us the universe from the natural observatory where we are placed. But to obtain a more complete idea of its constitution, of the infinite variety of its members, we must descend from those regions, where the sight and mind are lost, to a group, nearer to us, and therefore more accessible to the investigations of man—to that group, or system, of which the earth forms part.

Of this the sun is the centre.

Round this focus of light and heat, but at various distances, revolve more than a hundred secondary bodies—Planets, some of which are accompanied by smaller ones—Satellites. Not self-luminous, they would be invisible to us, if the light, which they receive from the sun, were not reflected toward the earth, making them also appear as luminous points spread over the celestial vault like so many stars. Such would be the appearance of the earth seen in space, at a distance sufficiently great.

A common character distinguishes all the celestial bodies that form part of this group—the Solar System—from the multitude of other stars. For while the suns, composing what is called the Sidereal Universe, are situated at distances seemingly infinite, the bodies composing the group of which we speak are relatively much nearer the earth, are, in fact, our neighbors.

What results from this double fact? Two very simple consequences, easily understood.

The first is, that the stars do not undergo any sensible change of position in the starry vault. Their distance is such that they appear actually at rest in the depths of space; hence the term Fixed Stars—now abandoned, because a minute and elaborate study of their relative positions has established the fact that the stars really do move in the remote regions of the heavens. The apparent immobility of which we have spoken, and which is one of their characteristics, is evidenced by the uniformity of appearance preserved for centuries by the artificial groups of stars, to which the name of Constellations has been given.

Now, it is otherwise with the bodies that revolve round our sun: they are near enough to the earth to allow of their displacements in space being perceived in short intervals of time. Traveling, by virtue of their proper motions along the starry vault, distances which appear greater as their own distance from us is less, these bodies received at the outset the name they have since retained—Planets, or Wandering Stars.

It is thus that, when we stand in the middle of an extensive plain, we judge distant objects—those that border the horizon—to be immovable; while we instantly perceive the slightest change of place in the near ones. It is true that when we ourselves move, the real movements become complicated with the apparent movements, but the former must be distinguished, if we wish to have an exact idea of the actual course traveled. This complication of the apparent movements of the planets—a necessary consequence of the movement of the earth—is one of the most striking testimonials to the reality of the latter; but it must also be added, that this was precisely the stone of stumbling of ancient astronomy until the time—and that not long ago—when the real movements were made known. Movements of rotation, movements of revolution, around the common centre, the duration of these movements, distances, forms and dimensions, distribution of light and heat, all change in passing from one planet to another. And yet, marvelous thing, the same laws govern, all in such a way that the unity of plan is not less marked than the astonishing variety of the phenomena.

One circumstance common to all the bodies of the solar system forcibly strikes the imagination. It is, that these enormous masses—these globes, many of which are much heavier than the earth, and lastly, the earth itself—are not only suspended in space, but move through the ether with velocities truly stupendous.

Imagine yourself a spectator, standing immovable in space. A luminous body appears in the distance, little by little you see it approach and increase in size; its immense circumference, which exceeds a hundred thousand leagues, is in rapid rotation, which makes each point on its periphery travel through nine miles a second. The globe itself passes before you, carried through space with a velocity twenty-four times greater than that of a cannon-ball. In such a way Jupiter would appear to you traveling in its orbit. This headlong course would banish it forever to the most remote regions of the visible universe, if it were not subdued and held by the powerful attraction of a globe a thousand times larger than its own—by the sun himself. Not only does astronomy show, by undeniable proofs, the reality of these marvelous movements—not only has she arrived at the knowledge of their invariable constancy, at least during thousands of centuries; but she has found in their very rapidity the cause of the stability of all the celestial bodies.

If there is difficulty in imagining such masses freely circulating in the ether, how much more are we impressed when we consider that these rapid movements are not confined to the planets; and when we look upon the sun with all his retinue as moving in an orbit yet unknown, himself attracted no doubt by a more powerful sun, or by a group of suns! All the stars which by reason of their infinite distances appear immovable, move in different directions; and we shall see later, that if these movements are performed with extreme slowness, the slowness is apparent only. In reality, these are the most rapid celestial movements that we know of.

Thousands of centuries will be necessary before these immense sidereal voyages are accomplished. Their vast periods are to the length of our year what the dimensions of the earth are to the distances of the stars; and, according to the happy expression of Humboldt, they make of the universe an eternal timekeeper. Thus, in the contemplation of celestial phenomena, the idea of infinite duration impresses itself on the mind with the same irresistible power as the idea of the infinity of space.

FOOTNOTES:

[1] Via Lactea. It is also called the Galaxy, from the Greek word for the same thing.

SPACE.—Richard A. Proctor

Although astronomy tells us in the clearest words of the vast depths of space which surround our earth on all sides, we are not thereby enabled to realize their enormous extension. It is not merely that the unknown depths beyond the range of our most powerful telescopes are inconceivable, but that the parts of space which we can examine are on too large a scale for us to conceive their real dimensions. It is hardly going too far to say that our powers of actual conception are limited to the extent of space over which the eye seems to range in the daytime. Of course, in the daytime, at least in clear weather, there is one direction in which the eyesight ranges over a distance of many millions of miles—namely, where we see the sun. But the sense of sight is not cognizant of that enormous distance, and simply presents the sun to us as a bright disk in the sky, or perhaps rather nearer to us than the sky. Even the distance of the sky itself is underestimated. A portion of the light we receive from the sky on a clear day comes from parts of the atmosphere distant more than thirty or forty miles from us; but the eye does not recognize the fact. The blue sky seems a little further off than the clouds, but not much; the light clouds of summer seem a little, but not much, further off than the heavier clouds of a winter sky; a cloud-covered winter sky seems a little further off than heavy rain-clouds. The actual varieties of distance among clouds of various kinds are not much more clearly discerned than the actual varieties of distance among the heavenly bodies. The estimate formed of the distance of a cloud-covered sky overhead probably amounts to little more than a mile, and it is very doubtful whether the mind presents the remotest depths of a blue sky overhead at more than two miles. Toward the horizon the distance seems greater, and probably on a cloudy day the sky near the horizon is unconsciously regarded as at a distance of about five miles, while blue sky near the horizon may be regarded as lying at a distance of six or seven miles, the arch of a blue sky seeming to be far more deeply curved than that of a cloud-covered sky.

It is to distances such as these that the mind unconsciously refers the celestial bodies. We know that the moon is about 2,000 miles in diameter, but the mind refuses to present her to us as other than a round disk much smaller than those other objects in sight which occupy a much larger portion of the field of vision. The sun can not be conceived to exceed the moon enormously in size, seeing that he appears no larger; and all the multitude of stars are judged by the sight to be mere bright points of light in reality as they appear to be.

How, then, can we hope to appreciate the vastness of space whereof astronomy tells us? To the student of science attempting to conceive the immensities of whose existence he is assured, the same lesson might be taught in parable which the child of St. Augustine’s vision taught the Numidian theologian. As reasonably might an infant hope to pour the waters of ocean into a hollow, scooped with his tiny fingers in the sand, as man to picture in his narrow mind the length and breadth and depth of the abysses of space in which our earth is lost.

Yet, as a picture of a great mansion may be so drawn on a small scrap of paper as to convey just ideas of its proportions, so may the great truths which astronomy has taught us about the depths of space be so presented that just conceptions may be formed of the proportions of at least those parts of the universe which lie within the range of scientific vision, though it would be hopeless to attempt to conceive their real dimensions.

When we learn that a globe as large as our earth, suspended beside the moon, would seem to have a diameter exceeding hers nearly four times, so that the globe would cover a space in the heavens about thirteen times as large as the moon covers, we form a just conception of the size of the moon as compared with the earth, though the mind can not conceive such a body as the moon or the earth really is. When, in turn, we are told that if a globe as large as the earth, but glowing as brightly as the sun, were set beside the sun, it would look a mere point of light, we not only learn to picture rightly to ourselves how largely the sun exceeds the earth, but also how enormous must be the real distance of the sun.

Another step leads us to a standpoint whence we can form a correct estimate of the vast distance of the fixed stars; for we can learn that so enormous is the distance of even the nearest fixed star, that the tremendous space separating the earth from that star sinks in turn into the merest point, insomuch that if a globe as bright as the sun had the earth’s orbit as a close-fitting girdle, then this glorious orb (with a diameter of some 184,000,000 of miles) would look very much smaller than such a globe as our earth would look at the sun’s distance—would, in fact, occupy but about one-fortieth part of the space in the sky which she, though she would then look a mere point, would occupy if viewed from that distance.

But there is a way of viewing the immensities of space which, though not aiding us indeed to conceive them, enables the mind to picture their proportions better than any other. The dimensions of the earth’s path around the sun sink into insignificance beside those of the outermost planets; but these in their turn dwindle into nothingness beside those of some among the comets. From the path of these comets, if only sentient and reasoning beings could trace out in a comet’s company those mighty orbits, and could have for the duration of their existence not the brief span of time which measures the longest human life, but many circuits of their comet home around the same ruling orb (as we live during many circuits of our globe around the sun), the dimensions of the star-depths, which even to scientific insight are all but immeasurable, would be directly discernible. Not only would the proportions of that mighty system be perceived, whose fruits and blossoms are suns and worlds, but even the gradually changing arrangement of its parts could be discerned.

Some comets, indeed, do not travel around the sun, but flit from sun to sun on journeys lasting millions of years, paying each sun but a single visit. A being inhabiting such a comet, and having these interstellar journeys as the years of his existence, so that he could live through many of them, would have a wonderful insight into the economy of the stellar system. If his powers of conception as far exceeded ours as the range of his travels and the duration of his existence, he would be able to recognize the proportions of a large part of the stellar universe as clearly as we recognize the proportions of the solar system.

But leaving these wonderful wanderers, whose journeys are as far beyond our powers of conception as the immensity of the regions of star-strewn space, we may find, among the comets belonging to the sun’s domain, bodies whose range of travel would give their inhabitants far clearer views of the architecture of the heavens than even the profoundest terrestrial astronomer can possibly obtain.

Such a comet as Halley’s, for instance, though one of comparatively limited range in space, yet travels so far from the sun that, from the extreme part of its path, it sees the stars displaced nearly twenty times as much (owing to its own change of position) as they are from the earth on opposite sides of her comparatively narrow orbit. And the length of this comet’s year, if it indicated the lives of all creatures traveling along with it, would suggest a power of patiently watching the progress of changes lasting not a few of our years only, but for centuries. Seventy-five or seventy-six years elapse between each return of this comet to the sun’s neighborhood, and one who should have lived during sixty or seventy circuits of this body around its mighty orbit would have been able to watch the rush of stars, with their velocities of many miles per second, until visible displacements had taken place in their positions.

This, however, is as nothing compared with the mighty range in space and the enormous period of the orbit of the great comet of the year 1811. This comet is, on the whole, the most remarkable ever known. It was visible for nearly seventeen months, and though it did not approach the sun within 100,000,000 miles, and was therefore not subject to that violence of action which has caused enormous tails to be thrown out from comets which have come within a few million miles of him, or even within less than a quarter of his own diameter, it flourished forth a tail 120,000,000 of miles in length. Its orbit has, according to the calculations of the astronomer Argelander, a space exceeding the earth’s distance from the sun 211 times, and thus surpassing even the mighty distance of Neptune fully seven times. It occupies in circuiting this mighty path no less than 3,065 of our years (with a possible error either way of about forty-three years). So that, according to Bible chronology, this comet’s last appearance probably occurred during the rule of the Judge Tola, son of Puah, son of Dodo, over the children of Israel, though it may have occurred during the rule of his predecessor Abimelech, or during that of his successor Jair.[2] During one-half of the enormous interval between that time and 1811 the comet was rushing outward into space, reaching the remotest part of its path somewhere about the year 278 (A. D.), and from that time to 1811 it was on its return journey. It is strange to think, however, that though the remotest part of its path lay 211 times further from the sun than the earth’s orbit, yet even this mighty path, requiring more than 3,000 years for a single circuit, can not be said to have carried the comet into the star-depths. If the earth were to shift its position by the some enormous amount, the nearest fixed star would have its apparent position changed only by about an eighth part of the apparent diameter of the sun or moon, or by about one-quarter of the distance separating the middle star of the Bear’s tail from its close companion.

But this fact of itself is most strikingly suggestive of the vast distance of the stars. For consider what it means. Imagine the middle star of the Bear’s tail to be the really nearest of all the stars instead of lying probably twenty or thirty times further away. Conceive a comet belonging to that sun after making its nearest approach to it to travel away upon an orbit requiring 3,000 years for each circuit. Then (supposing that star equal to our sun in mass) the comet, though rushing away from its sun with inconceivable velocity during 1,500 years, would, at the end of that vast period, seem to be no further away than one-fourth of the distance separating the sun from its near companion. Look at the middle star of the Bear’s tail on any clear night, and on its small satellite, remembering this fact, and the awful immensity of the star-depths are strongly impressed upon the mind. But the observer must not fail to remember that the star really is many times more remote than we have here for a moment supposed, and that such a comet’s range of travel would be proportionately reduced. Moreover, many among the stars are doubtless hundreds, even thousands, of times still further away.

Let us turn lastly to the amazing comet of the year 1744. We find that though it had the longest period of any which has ever been assigned to a comet as the result of actual mathematical calculation, yet its range in space would scarcely suffice to change the position of the stars in such sort that the aspect of the familiar constellations would be materially altered. Euler, the eminent mathematician, calculated for this comet a period of 122,683 years, which would correspond, I find, to a distance of recession equal to 2,469 times the distance of the earth from the sun, or about eighty times the distance of Neptune. Yet this is but little more than twelve times the greatest distance of the comet of 1811. Probably the actual range of such an orbit from the middle star of the Bear’s tail would be equal in appearance to the range described above on the supposition that the star is no further from us than the nearest known star (Alpha Centauri). That is, such a comet, if it could be seen and watched during a period of about 122,000 years, would seem to recede from the star to a distance equal to about one-fourth the space separating it from its close companion, and then to return to the point of nearest approach to its ruling sun.

Such are the immensities of star-strewn space! The journey of a comet receding from the sun with inconceivable velocity during hundreds of thousands of years carries it but so small a distance from him compared with the distance of the nearest star as scarcely to change the appearance of the celestial landscape; and yet the distances separating the sun from the nearest of his fellow suns are but as hairbreadths to leagues when compared with the proportions of the scheme of suns to which he belongs. These distances, though so mighty that by comparison with them the inconceivable dimensions of our own earth sink into utter nothingness, do not bring us even to the threshold of the outermost court of that region of space to which the scrutiny of our telescopes extends. Yet the whole of that region is but an atom in the infinity of space.

FOOTNOTES:

[2] It might be suggested that the appearance of this blazing comet among the stars drove the more superstitious of the Israelites at that time to the worship of star-gods, as we read how, during the Judgeship of Jair, they “served Baalim and Ashtaroth, and the gods of Syria and the gods of Moab, and the gods of the Philistines, and forsook the Lord and served not Him.” To a people like the Jews, who seem to have been in continual danger of returning to the Sabaistic worship of their Chaldean ancestors, the appearance of a blazing comet may have been a frequent occasion of backsliding.

EXTENT OF THE SIDEREAL HEAVENS.—Sir Robert S. Ball

Of all the discoveries that have ever been made in science there are two which especially baffle our powers of comprehension. They lie at the opposite extremes of nature. One relates to objects which are infinitely small, the other relates to objects which are almost infinitely great. The microscope teaches us that there are animals so minute that if a thousand of them were ranged abreast they would easily swim without being thrown out of line through the eye of the finest cambric needle. Each of those minute creatures is a highly organized number of particles, capable of moving about, of finding and devouring its food, and of behaving in all other respects as becomes an animal as distinguished from an unorganized piece of matter. The mind is capable of realizing the structure of these little creatures, and of fully appreciating their marvelous adaptation to the life they are destined to lead. If these animals excite our astonishment by reason of their extreme minuteness, there is an appeal made to conceptions of an entirely different character when we learn the lessons which the telescope teaches. As the microscope reveals the excessively minute, so does the telescope disclose the sublimely great. In each case myriads of objects are submitted to our astonished view, but while the microscope brings before us creatures of which countless millions could swim about freely in a thimbleful of water, the telescope conducts our vision to uncounted legions of stars, many of them millions of times larger than the earth.

The grandest truth in the whole of nature is conveyed in that first lesson in astronomy which answers the question: What are the stars? This is a question that a child will ask, and I have heard of a child’s pretty idea that the stars were little holes in the sky to let the glory of heaven shine through. The philosopher will replace this explanation by another hardly less poetical, which will enable us to form some more adequate notion of the real magnificence of the universe. Each star that we see is, it is true, only a glittering little point of light, but that is merely because we are a long way from it. An electric light which will dazzle your eye when quite close will be reduced to an agreeable illumination if it is at a little distance, will become a faint light a mile away, and at no great distance will become altogether invisible. We must remember that out in space there is plenty of room—there are no bounds; and therefore when we see light glistening in the far distant depths we can not at once conclude that the light is a faint one because it appears to us to be faint. It may be that the light is only faint because it comes from such a tremendous distance. In fact, the brightest light conceivable could be reduced to the insignificance of a small star if only it were removed sufficiently far.

The most intense light we know of comes, of course, from the light which rules by day, from our sun himself. The sun pours his unrivaled beams around us in all directions with prodigal abundance, notwithstanding his enormous distance of ninety-three millions of miles. Let me describe an experiment with respect to our sun, an experiment, it is needless to say, which could never be performed, but the results to which it leads us are none the less certain. Astronomers have demonstrated them in many other ways.

Suppose that the sun were gradually to be moved away further and further into space; suppose that by this time to-morrow the great luminary should be twice as far as it is now, and the next day should be three times as far, and the day after that four times, and so on until in a year’s time we should find that the sun was 365 times the distance from us that it is at present. Let us now trace the changes which we should see in the brilliancy of our orb of day. When he had reached double his distance from us, we should find that the light had decreased to a quarter of its present amount, and the heat which we derived from his beams would have decreased in the same proportion. In ten days we should find that the light had become so feeble as to be only one-hundredth part of that which we enjoy now. The apparent size of the sun would also be steadily decreasing, for as the distance of a body increases its apparent dimensions diminish. Sometimes the diminution of apparent size with distance is well illustrated on a clock tower. You would hardly believe that the hands and face of a clock like that at Westminster were so large until you happen to see a man cleaning or repairing it, when he appears a mere pigmy in comparison with the mighty dial which points out the hours. In a similar way with every increase of distance, the apparent size of the sun would decline, and in the lapse of a year the sunlight would be reduced to a feeble twilight. The sun itself would remain visible for many years, even if it were steadily moving away, though its lustre would continually decline, and its size would continually diminish, until at last it would have shrunk to the insignificance of a small point of light, still visible as a glittering object, but too minute to enable any definite form to be perceived.

Further still, the sun might recede until it passed beyond the reach of vision of the unaided eye; the telescope would, however, be able to pursue the retreating luminary until at last it sank into the depths of space beyond the reach of any instrument whatever.

This little argument will prepare us for an explanation of the stars. They merely appear to us to be points of light of varying degrees of brightness, but we have seen that our own sun might be reduced in lustre to that of the very dimmest of the stars if only it were removed sufficiently far. If, therefore, the stars are at a great enough distance from our system, it may indeed be that they also are suns, possibly equaling, or possibly even surpassing, our own sun in magnificence.

Here is indeed an imposing suggestion. Can it be that the host of stars which adorn our midnight sky are actually suns themselves of an importance comparable with that of our own? This is a great thought, and we desire to test it by every means in our power. You will see from the reasoning I have given that the whole question turns simply on one point, and that is: How far off are the stars?

The tiniest point of light that is just seen as a glimmer in the mightiest of telescopes may be indeed a sun as great, or indeed a million times greater, than our sun, if only that star be sufficiently far off. To find the distance of a star is a problem which taxes the utmost powers of the painstaking astronomer; every refinement of skill in making his measurements and of care in the calculation of his observations have to be lavished on the operation. Alas! it but too often happens that the astronomer’s labors prove to be futile. The surveying navigator often has to mark on his chart that no bottom could be found in the depths of the sea. His appliances would not work, or work reliably, in those ocean abysses; so, too, the astronomer, when he tries to sound the depths of space to the distances of the stars, has also to mark, generally speaking, “No bottom here,” as the result of most of his investigations. When this is the case we know for certain that the star on which his calculations have been made must be a gorgeous sun, because we are assured of the greatness of its distance, even though we have not been able to find out what that distance was. There are, however, some few places through the sky where the astronomer’s sounding line can, so to speak, touch bottom; there are a few stars of which we do know the distance, and the result is not a little significant. Were our sun to be withdrawn from us to a distance so great as that of the very nearest of the stars, our magnificent ruler and benefactor would certainly have lost all his splendor; he would, in fact, have shrunk to the similitude of a little star not nearly so bright as many of those which we see over our heads every night. Imagine the sun’s light subdivided into two hundred thousand parts, each of which would give us only a feeble illumination, and then imagine that each of these parts was again divided into two hundred thousand parts more, and it is one of these last fragments that would represent the miserable lustre which the sun would then display.

From these considerations we can enunciate the magnificent truth which astronomy discloses to us. I do not think that in the whole range of nature there is any thought so magnificent or so imposing as that which teaches us to regard every star of every constellation as a sun. We can not indeed assert that they are all so great as our sun, but we can affirm with certainty that many of them are far greater and far more splendid. Considering that our sun presides over a system of worlds of which the earth is one, that it gives light and heat to those worlds, and guides them in their movements, it would greatly enlarge our conceptions of the universe if we were assured that there was even one more sun as large and as splendidly attended as is our own. But now we find that not only is there one additional sun, but that they teem in uncounted thousands through space. Look, for example, on the next fine night at the Great Bear, the best known of all our northern constellations, and there you see seven stars forming the well-known feature. Figure in your mind’s eye each one of those stars in the likeness of a majestic sun, as big, warm, and bright as our sun, and look at other parts of the sky and repeat the process with the other constellations, and your conception of the magnificence of the starry system will begin to assume proper proportions. But this is only the first step, you must next look at the smaller stars, and reflect that they, too, are also suns, only much further off as a general rule than the brighter stars, though this is by no means invariably the case. Thus your estimate of the number of suns in the universe will rise to thousands, but you will not stop there, you will get a telescope to help you, and, to your extreme delight and wonder, you will find that there are hosts of stars—too faint to be visible to the eye, but which the telescope will immediately disclose. You will get a more powerful instrument, and then you will perceive that the stars are to be numbered by tens of thousands, and even by millions, and with every fresh accession of power in your telescope fresh troops and myriads of suns are revealed. Suns in clusters, suns strewn thickly here and sparsely there, so as to give us the notion that the only limit to the number we can see is the power of the telescopes we are using. Attempts at actual numeration are futile, for who can tell the number of the stars?

We can, however, form an estimate, and by taking samples, so to speak, of the sky here and other samples there, we have been enabled to learn the overwhelming fact that our universe does contain at the very least one hundred millions of suns.

In discussing the extent of the visible universe, it must always be borne in mind that the further a source of light is from us the fainter is the illumination which we receive from it. Suppose that a star which just lies on the limits of naked-eye visibility were somehow to be transported to a distance which is twice as great, then the lustre of that star would be diminished to one-fourth of its original amount. It would, therefore, be of course invisible to the unaided eye, but could still be easily perceived by a telescope. Indeed, the very word telescope means an instrument for looking at objects a long way off, and the effect of the telescope is to reduce the apparent distance of the object.

The bulk of a grain of sand as compared with the bulk of a football may illustrate the space accessible to our eyes when compared with the space accessible to one of the great telescopes. The larger of these spaces has a thousand times the diameter of the others; therefore, the relative quantities of these spaces are to be obtained by multiplying 1,000 by 1,000 and by 1,000 again. Thus we finally learn that the amplitude of our vision is augmented to one thousand million times its original extent by the use of our greatest telescopes. It need, therefore, be no matter for surprise that the number of stars visible through our great telescopes or recorded on the sensitive films of photographic plates should number scores of millions. In fact, it would sometimes seem surprising that the number of telescopic stars is not even greater than it actually appears to be. If we are able to explore one thousand million times as much space, we might expect that the number of objects disclosed would be also increased about a thousand million-fold, but this is certainly not the case. The truth seems to be that our sun is but one star of a mighty cluster of stars; we happen to lie near the middle of the cluster, and the rest of the stars belonging to it form what we know as the Milky Way. There are, of course, other clusters scattered through the heavens, some of them, perhaps, as great as that body of stars which forms the Milky Way. Owing to our residence in this cluster we see the neighboring suns in multitudes, and thus we receive the impression that the solar system lies in an exceptionally rich part of the universe in as far as the distribution of stars is concerned.

On the outskirts of the universe lie those faintest and dimmest of objects which we can just perceive through our greatest telescopes. We know that many of the stars around us would still remain visible in great instruments, even though they were removed a thousand times as far off. Among the myriads of faint stars which we see from our observatories, there may be many, indeed there must be many, which are fully a thousand times as distant as the bright stars which twinkle in our comparative neighborhood. We thus obtain some conception of the stupendous distance at which the outskirts of the universe are situated.

There are different ways of illustrating this point, but I think the simplest, as well as the most striking, is that which is founded on the velocity of light. It is a remarkable fact that the beautiful star known as Vega[3] has a distance from us so tremendous that its light must have taken somewhere about eighteen years to travel hither from thence. Notwithstanding that the light dashes along with such inconceivable speed that it will cover 185,000 miles in every second, notwithstanding that a journey at this pace will complete the entire circuit of this globe seven or eight times between two successive ticks of the clock, the light will, nevertheless, take eighteen years to reach our eye from the time it leaves Vega. We do not, therefore, see the star as it is at present; we see it as it was eighteen years ago. For the light which this evening enters our eyes has been all that time on its journey. Indeed, if Vega were actually to be blotted out from existence it would still continue to shine out as vividly as ever for eighteen years before all the light on its way had reached us.

We have been led to the belief that among the more distant stars in the universe there must be many which are fully a thousand times as far from us as is Vega, hence we arrive at the startling conception that the light they emit has been on its journey for 18,000 years before it reached us. When we look at those lights to-night we are actually viewing them as they were 18,000 years ago. In fact, those stars might have totally vanished 17,000 years ago, though we and our descendants may still see them glittering for yet another thousand years.

We shall realize a little more fully what this reasoning involves if we suppose that astronomers dwelt on such a star, and that they had eyes and telescopes sufficiently keen not only to discern our little earth, but even to scrutinize its surface with attention. Let us suppose that the stellar astronomers looked at England: do you think they would see a network of railways joining mighty and populous cities, furnished with immense manufactories and with countless institutions? Such would be the England of to-day. But from the distance at which these astronomers are situated light takes 18,000 years for its journey, and, therefore, what they would see would be England as it was 18,000 years ago. To them England would even now appear as a country mainly covered with forests inhabited by bears and wolves, and totally void of any trace of civilization. This illustration will, at all events, serve to convey some conception of the distance at which the outskirts of our visible universe are plunged in the depths of space.

FOOTNOTES:

[3] Vega is the brightest star in the Lyre and is nearly always at night directly overhead in our latitude.—E. S.

THE STARS.—Amédée Guillemin

No sight is at once so awe-inspiring and so grand as that of the heavens on a beautiful night. If care be taken to choose as a standpoint for observation an open place, such as a plain or the summit of a hill on land, or, again, the open sea, and if the atmosphere, somewhat charged with dew, possesses all its transparency and purity, we shall see thousands of luminous points twinkling in all directions, accomplishing slowly and together their silent march. The contrast of the obscurity which reigns on the surface of the earth with the brightness of that resplendent vault gives an indefinite depth to the celestial ocean that deepens over our heads. But let us here leave the magnificence of the spectacle to study it in its most minute details.

Let us commence with the appearances. A characteristic common to all the stars is an incessant and very rapid change of brightness, which has received the name of scintillation. This is accompanied by variations of color equally rapid, due to the same cause as the successive disappearances and reappearances. All stars scintillate, whatever may be their brilliancy, at least in our temperate regions. But the intensity of this luminous movement is not the same in all, and it varies, moreover, both with the degree of purity of the sky, the elevation of the stars above the horizon, and the temperature of the night.

According to Arago, scintillation is due to the difference of velocity of the various colored rays traversing the unequally warm, unequally dense, unequally humid atmospheric strata. Thus, in tropical regions, where the atmospheric strata are more homogeneous, scintillation is rarely observed in stars the elevation of which above the horizon is more than 15°, or the sixth of the distance of the horizon from the zenith. “This circumstance,” says Humboldt, “gives to the celestial vault of these countries a particularly calm and soft character.”

Another specific character of the stars is that their diameters are without appreciable dimensions. To the naked eye, this distinction would be insufficient, since, the moon and the sun excepted, the most considerable planets have not sensible diameters. But, while the magnifying power of optical instruments shows us the principal planets under the form of clearly defined disks, the most powerful glasses only show a star as a luminous point. The distance which separates us from these bodies is so great that there is nothing to astonish us in such a result.

Wollaston affirms that the apparent diameter of the most brilliant star in the heavens, Sirius, is not more than the fiftieth part of a second of an arc. But let us hasten to say that this result still leaves a good margin as to the real dimensions of the star, since, at the distance of Sirius, an apparent diameter would represent a real diameter of 11,000,000 miles; that is, twelve times the diameter of our sun.

Let us add, lastly, that the absence of appreciable dimensions does not suffice to distinguish absolutely the stars from the planets, since a certain number of the latter, as we have before seen, appear in telescopes only as simple luminous points. Let us come, then, to a permanent specific characteristic, the knowledge of which will always prevent us from confounding a star with one of the known or unknown bodies which form part of our solar group. This characteristic is as follows:

The stars, properly so called, preserve among themselves—nearly enough for our present purpose—the same relative distances. They form, then, on the celestial vault apparent groups, the configuration of which is nearly invariable. Centuries must elapse to show a change of form, unless we employ extremely delicate measures. A planet, on the contrary, moves rapidly across these groups, to such a degree that, in the interval of a night, or at most of a few nights, this displacement is very perceptible; hence the old denomination of fixed stars, in opposition to the wandering ones, or planets.

We must be careful, however, to guard against assigning to this word a rigidity which it does not possess, for the stars really move with a velocity not inferior to that which animates the members of our system. Their immense distance is the only cause of their apparent immobility, which vanishes when precise observations, embracing a sufficient interval of time—some years, for example—are made.

A fact which strikes every one is the great diversity of brightness in the stars which people the heavens. All degrees of intensity are remarked, from the resplendent light of Sirius to the scarcely perceptible glimmer of those hardly visible to the naked eye.

Whence arises this difference of brightness? This question we can not answer for any star in particular, but it is easy to imagine that it may result from various circumstances, such as their less or greater distance, the real and various dimensions of the bodies, and, lastly, the intrinsic brightness of the light peculiar to each. However this may be, astronomers without regard to the unknown causes which may influence the intensity of the stellar light, have divided stars into classes or magnitudes; and when we speak of a star of the first, second, or fifth magnitude, it is understood that this way of speaking refers only to the apparent brightness, and that nothing is affirmed either as to the real dimensions or distance, or even intrinsic brightness.

Besides, as the stars, arranged in the order of their brightness, would form a progression decreasing by imperceptible degrees, the classes adopted are themselves conventional and arbitrary. The first six magnitudes comprise all stars visible to the naked eye. But the use of the most powerful telescopes brings to view stars of feebler light, descending to the sixteenth and seventeenth magnitudes. In truth, the progression has no inferior limit: it extends more and more in proportion as the progress of the optician’s art increases the penetrating power of our instruments.

To gain an idea of the respective intensities of the light emitted by the stars of the first six magnitudes, following the scale adopted by astronomers, the accompanying illustration (Fig. 1), should be inspected; in it the stars are figured by disks, the surfaces of which are in proportion to their brilliancy.

But, we repeat, it must not be thought that the stars ranked in the same class are, on that account, of the same brightness. Thus the light of Sirius is estimated at four times the star Alpha Centauri; but both, nevertheless, are included by astronomers in the number of the stars of the first magnitude.

Fig. 1.—Relative Brilliancy of Stars of the first Six Magnitudes

We here give the names of the twenty most brilliant stars of the two hemispheres which it is usual to consider as forming the first class. They are here arranged in the order of their brightness:

Lastly, Regulus, a bright star in the constellation of the Lion, is also ranked by some astronomers in the first magnitude, while others only admit in this class the first seventeen stars in the above list. These divergences are of no importance.

In proportion as the scale of brilliancy or magnitude is descended, the number of the stars contained in each class rapidly increases. The number of second magnitude stars in the heavens is about 65; of the third, about 200; of the fifth, 1,100; and of the sixth magnitude, 3,200. Adding these numbers together, we obtain a few over 5,000 stars of the first six magnitudes, and these comprise very nearly all those that can be seen with the naked eye.

The smallness of this number nearly always astonishes those who have not tried to form an exact estimate of the number of stars which shine in the celestial vault on the most favorable nights.

The aspect of the multitude of sparkling points which are scattered over the sky makes us disposed to believe that they are innumerable, and to be counted, if not by millions, at all events by hundreds of thousands. This is, nevertheless, an illusion. All observers who have taken the trouble to make an exact enumeration of the stars visible to the naked eye have arrived at a maximum of 3,000 as the mean number which can be observed in every part of the heavens, visible at the same time, at the same place; this, of course, is but half of the entire heavens.

Argelander has published an exact catalogue of the stars visible on the horizon of Berlin during the course of the year. This catalogue comprises 3,256 stars. According to Humboldt, there are 4,146 visible on the horizon of Paris in the whole course of the year; and as this number increases in proportion as we approach the Equator, that is to say, in proportion as the double movement of the earth unfolds to us during a year a more extensive portion of the heavens, 4,638 stars are already visible to the naked eye on the horizon of Alexandria.

We repeat, the maximum number is comprised between 5,000 and 6,000 stars for the entire heavens, including those seen by the most piercing and most accustomed eyes in the best nights for observation. When the atmosphere is lit up by the moon, or by twilight, or, as happens in the great centres of population, by the illumination of the houses and streets, the lowest magnitude stars are effaced altogether, and the number of those visible is consequently much more limited. We may add in conclusion, that the more the scintillation, the more easy it is to distinguish very faint stars.

A word now on the number of stars that can be seen with the help of the telescope. Here we shall find the numbers which our imagination had erroneously led us to believe are visible to the naked eye.

According to the illustrious director of the Observatory of Bonn—Argelander—the seventh magnitude comprises nearly 13,000 stars; the eighth, 40,000; and, lastly, the ninth, 142,000. The calculations of Struve give the total number of stars visible in the entire heavens by the aid of Sir William Herschel’s 20-foot reflector as more than 20,000,000. But, without doubt, these approximate numbers are much below the real ones. It will be seen, besides, that the richness of the heavens in stars is very unequal. The bright zone known under the name of the Milky Way alone contains, according to Herschel, 18,000,000.

THE LUCID STARS.—J. E. Gore

The term “lucid” has been applied to the stars visible to the naked eye, without optical aid of any kind.[4] Many people think that the number of stars visible in this way is very large. But in reality the number visible to the naked eye is comparatively small. Some persons are, of course, gifted with very keen eyesight—“miraculous vision” it is sometimes called—and can see more stars than others; but to average eyesight the number visible in this way, and which can be individually counted, is very limited. The famous Hipparchus formed a catalogue of stars in the year 127 B. C. This presumably contained all the most conspicuous stars he could see in his latitude, and it includes only 1,025 stars. Al-Sûfi, the Persian astronomer, in his Description of the Fixed Stars, written in the Tenth Century, describes the positions of only 1,018 stars, although he refers to a number of other faint stars, of which he does not record the exact places. Pliny thought that about 1,600 stars were visible in the sky of Europe.

In modern times, however, a considerable number of fainter stars have been recorded as visible to the naked eye. The famous German astronomer, Heis, who had keen eyesight, records the positions of 3,903 stars north of the Equator, and 1,040 between the Equator and 20 degrees south declination, or a total of 4,943 stars between the North Pole and 20 degrees south of the Equator. This would, I find, give a total of about 7,366 stars for both hemispheres if the stars were equally distributed. Behrmann, in his Atlas of Southern Stars, between 20 degrees south declination and the South Pole, shows 2,344 stars as visible to the naked eye. This would give a total of 7,124 for both hemispheres. The actual number seen by Heis and Behrmann in both hemispheres is 4,943 + 2,344, or 7,287 stars. The Belgian astronomer, Houzeau, published a catalogue and atlas of the stars in both hemispheres, made from his own observations in Jamaica and South America, and finds a total of 5,719 stars in the whole sky. As all these observers had good eyesight, we may take a mean of the above results as the total number visible to the naked eye in the whole star sphere. This gives 6,874 stars, or in round numbers we may say that there are about 7,000 stars visible to average eyesight in both hemispheres. This gives, of course, about 3,500 stars to one observer at the same time at any point on the earth’s surface.

As the whole star sphere contains an area of 41,253 square degrees, we have an average of one star to six square degrees. In other words there is, on an average, one lucid star in a space equal to about thirty times the area covered by the full moon! This result may seem rather surprising considering the apparently large number of stars visible to the naked eye on a clear night, but the fact can not be denied. The stars are not, of course, equally distributed over the surface of the sky, but are gathered together in some places, and sparsely scattered in others, and this may perhaps help to give the impression of a greater number than there really are.

That the stars are of various degrees of brightness was recognized by the ancient astronomers. Ptolemy divided them into six classes, the brightest being called first magnitude, those considerably fainter the second, those much fainter still the third, down to the sixth magnitude, which were supposed to be the faintest just visible to the naked eye on a clear moonless night. Ptolemy only recorded whole magnitudes, but Al-Sûfi, in the Tenth Century, divided these magnitudes, for the first time, into thirds. Thus a star slightly less than an average star of the second magnitude he called 2—3, that is nearer in brightness to 2 than to 3; one a little brighter than the third he recorded as 3—2, or nearer to 3 than to 2, and so on. This method has been followed by Argelander, Behrmann, Heis, and Houzeau, but in the photometric catalogues of Harvard, Oxford, and Potsdam the magnitudes are measured in decimals of a degree. This has been found necessary for greater accuracy, as the heavens contain stars of all degrees of brightness.

The term “magnitude” means the ratio between the light of a star of a given magnitude and that of another exactly one magnitude fainter. This ratio has been variously estimated by different astronomers, and ranges from 2.155, found by Johnson in 1851, to 3.06, assumed by Pierce in 1878. The value now universally adopted by astronomers is 2.512 (of which the logarithm is 0.4). This number is nearly a mean of all the estimates made, and agrees with the value found by Pogson in 1854 by means of an oil flame, and by Rosen with a Zöllner photometer in 1870. It simply means that an average star of the first magnitude is 2.512 times the brightness of a star of the second magnitude; a star of the second, 2.512 times brighter than one of the third, and so on. This makes a star of the first magnitude just 100 times brighter than one of the sixth.

There are several stars brighter than an average star of the first magnitude, such as Aldebaran. These are Sirius, which is nearly 11 times brighter than Aldebaran (according to the revised measures at Harvard); Canopus, the second brightest star in the heavens, and about two magnitudes brighter than Aldebaran; Arcturus, Capella, Vega, Alpha Centauri, Rigel, Procyon, Alpha Eridani, Beta Centauri, and Alpha Orionis. Al-Sûfi rated 13 stars of the first magnitude, visible at his station in Persia, and Halley enumerates 16 in the whole sky. According to the Harvard photometric measures, there are 13 stars in both hemispheres brighter than Aldebaran, which is rated 1.07.

As average stars of the different magnitudes the following may be taken as examples, derived from the Harvard measures: First magnitude, Aldebaran and Spica; second magnitude, β Aurigæ and β Canis Majoris; third magnitude, ι Aurigæ and β Ophiuchi; fourth magnitude, θ Herculis and ε Draconis; and fifth magnitude, ρ Ursæ Majoris and ω Sagittarii. Stars of about the sixth magnitude are, of course, numerous, and lie near the limit of naked-eye vision for average eyesight, although on clear moonless nights still fainter stars may be “glimpsed” by keen-eyed observers.

The stars have been divided into groups and constellations, now chiefly used for the purpose of reference, but in ancient times they were associated with the imaginary figures of men and animals, etc. The origin of these constellation figures is doubtful, but they are certainly of great antiquity. Ptolemy’s constellations were 48 in number, but different writers from the First Century B. C. give different numbers, ranging from 43 to 62. Bayer’s Uranometria, published in 1603, contains 60, 12 new constellations in the Southern Hemisphere having been added by Theodorus to Ptolemy’s original 48.

The figures representing the constellations were originally drawn on spheres, or celestial globes, as they are now called. The ancient astronomers attributed the invention of the sphere to Atlas. It seems certain that a celestial sphere was constructed by Eudoxus in the Fourth Century B. C. Strabo speaks of one made by Krates about the year 130 B. C., and according to Ovid, Archimedes had constructed one at a considerably earlier period. None of these ancient spheres has been preserved. There is, however, in the Vatican a fragment in marble of a Græco-Egyptian planisphere, and a globe in the museum of Arolsen, but these are of much later date. Our knowledge of the original constellation figures is derived from the accounts given by Ptolemy and his successors, and from a few globes which only date back to the Arabian period of astronomy. Among the Arabian globes still existing the most famous is one made of copper, and preserved in the Borgia Museum at Velletri in Italy. It is supposed to have been made by a person called Caisar, who was executed by the Sultan of Egypt in A. D. 1225. The most ancient of all is one discovered some years ago at Florence. It is supposed to date back to A. D. 1081, and to have been made by Meucci. There is also one in the Farnese Museum at Naples, made in A. D. 1225. Of modern celestial globes the oldest is one made by Jansson Blaeu in 1603. This gives all the constellations of the Southern Hemisphere as well as the Northern.

Ptolemy’s figures of the constellations were restored by the famous painter Albert Dürer of Nuremberg in 1515. The figures on modern globes and maps have been copied from this restoration. Dürer’s maps are now very rare.

In 1603, an atlas was published by Bayer. This was the first atlas to show the southern sky, and the first to designate the brightest stars by the letters of the Greek alphabet.[5] Flamsteed published an atlas in 1729. Maps and catalogues of the lucid stars have been published in recent times by Argelander, Behrmann, Heis, Houzeau, Proctor, and others. Of these Heis’s is, perhaps, the most reliable, at least so far as accurate star magnitudes are concerned. Houzeau shows both hemispheres, all the stars had been observed by himself in Jamaica and South America. Behrmann’s maps are confined to the Southern Hemisphere, between the South Pole and 20 degrees south of the Equator. The maps of the Uranometria Argentina, made at Cordoba in the Argentine Republic, show all the southern stars to the seventh magnitude, but many of these are beyond the reach of ordinary eyesight.

It is a well-known fact that the planets Venus and Jupiter are bright enough to form shadows of objects on a white background. It has also been found that the brightest stars, especially Sirius, are sufficiently brilliant to cast shadows. Kepler stated that a shadow was formed by even Spica, but I am not aware that this has been confirmed by modern observations.

There are some remarkable collections or clusters of stars visible to the naked eye, of these the Pleiades are probably the best known. To ordinary eyesight 6 stars are visible, but Möstlin, Kepler’s tutor, is said to have seen 14 with the naked eye, and some observers in modern times have seen 11 or 12. Other naked-eye clusters are the Hyades in Taurus, called Palilicium by Halley, and the Præsepe, or Bee-Hive in Cancer. Of larger groups, the Plow or Great Bear, Cassiopeia’s Chair, and Orion are probably known to most people.

Many of the lucid stars are double, that is, consist of two components, but most of these are only visible in powerful telescopes. There are, however, a few objects visible to the naked eye as double, and these have been called “naked-eye doubles,” although not strictly double in the correct sense of the term.

Ptolemy applied the term double to the star ν Sagittarii, which consists of two stars separated by a distance of fourteen minutes of arc, or about half the apparent diameter of the moon. According to Riccioli, Van der Hove saw two naked-eye doubles, one in Capricornus, 5 to 5½ minutes distant, and the other in the Hyades, 4½ or 5 minutes apart. The one in Capricornus was probably α, and the one in the Hyades θ Tauri. The middle star in the tail of the Great Bear, or handle of the Plow, has near it a small star, Alcor, which to many eyes is distinctly visible without optical aid. The famous Belgian astronomer, Houzeau, who seems to have had excellent sight, saw the star χ Tauri double, and 51 and 56 Tauri separated, also ι Orionis, and others.

Many of the stars are variable in their light, and several hundred of these curious and interesting objects are now known to astronomers. In a few of these the light changes may be followed with the naked eye. It is an interesting question whether any of the lucid stars have disappeared or changed in brightness since the early ages of astronomical observations. Al-Sûfi failed to find seven of Ptolemy’s stars, and Ulug Bekh, comparing his observations with the catalogues of Ptolemy and Al-Sûfi, announced twelve cases of supposed disappearance. Some of these may, however, be due to errors of observation. Montanari, writing in 1672, mentions two stars as having disappeared, namely β and γ of the constellation Argo, but these stars are now visible in the positions originally assigned to them.

In a careful examination of Al-Sûfi’s description of the stars written in the Tenth Century, and a comparison with modern estimates and measures, I have found several very interesting cases of apparent change in the brightness of the lucid stars. Al-Sûfi was an excellent and careful observer, and as a rule his estimates agree well with modern observations. We can therefore place considerable reliance on his estimates of star magnitudes. The Story of Theta Eridani has been well told by Dr. Anderson, and there seems to be no doubt that this southern star, which is now only of the third magnitude, was a bright star of the first magnitude in Al-Sûfi’s time! The following are other interesting cases of apparent change which I have met with in my examination of Al-Sûfi’s work. The Pole Star was rated third magnitude by both Ptolemy and Al-Sûfi, but it is now of the second magnitude, or a little less. The star γ Geminorum was rated third magnitude by Ptolemy and Al-Sûfi, or equal to δ Geminorum, but γ is now of the second magnitude, and its great superiority in brightness over δ is noticeable at a glance. Another interesting case is that of ζ and ο Persei, two stars which lie near each other, about seven degrees north of the Pleiades. Al-Sûfi distinctly describes these stars as both of the 3—4 magnitude; but Argelander, Heis, and the photometric measures at Harvard agree in making ζ about one magnitude brighter than ο. The stars being close are easily compared, and their present great difference in brightness is very noticeable. This is one of the most remarkable cases I have met with in Al-Sûfi’s work, and strongly suggests variation in ο, as ζ is still about the same brightness as Al-Sûfi made it. The identity of the stars is beyond all doubt, as Al-Sûfi describes their positions very clearly, and says there is no star between them and the Pleiades, a remark which is quite correct for the naked eye. The remarkable decrease in brightness of β Leonis (Denebola) since Al-Sûfi’s time has been considered in my paper on Some Suspected Variable Stars. That it was a bright star of the first magnitude is fully proved by the observations of Al-Sûfi and Tycho Brahe. These were careful and accurate observers, and they could not have been mistaken about a star of the first magnitude. β Leonis is now fainter than an average star of the second magnitude, and there can be no reasonable doubt that it has faded considerably since the Tenth Century.

There are some other discrepancies between Al-Sûfi’s observations and modern estimates, but the above are perhaps the most remarkable. With reference to lucid stars not mentioned by Al-Sûfi, he has not, I think, omitted any star brighter than the fourth magnitude in that portion of the sky visible from his station. There are, however, a number of stars between the fourth and sixth magnitudes which he does not mention. Of these the brightest seem to be ε Aquilæ, ρ and μ Cygni, and ζ Coronæ Borealis.

With reference to the distribution of the lucid stars in the sky there seems to be a well-marked tendency to congregate on the Milky Way. It is a remarkable fact that of the 15 brightest stars in the heavens, no less than 11 lie on or near the Milky Way, although the space covered by the Galaxy does not exceed one-fifth or one-sixth of the whole sky. From a careful enumeration of the stars in or near the Milky Way which I made some years ago, I found that of stars brighter than the fourth magnitude there are 118 on the Milky Way out of a total of 392, or about 30 per cent. From the Southern catalogue known as the Uranometria Argentina, Colonel Markwick, F.R.A.S., found 121 out of 228 stars to fourth magnitude, or a percentage of 53 per cent. These results seem to show some intimate relation between the lucid stars and the Galaxy.

FOOTNOTES:

[4] Except concave spectacles used by short-sighted persons.

[5] This custom has since prevailed. The following are the letters and their names:

THE CONSTELLATIONS.—Camille Flammarion

The earth is forgotten, with its small and ephemeral history. The sun himself, with all his immense system, has sunk in the infinite night. On the wings of inter-sidereal comets we have taken our flight toward the stars, the suns of space. Have we exactly measured, have we worthily realized the road passed over by our thoughts? The nearest star to us reigns at a distance of 275,000 times 37 millions of leagues—that is to say, at ten trillions[6] of leagues (about twenty-five billions of miles); out to that star an immense desert surrounds us, the most profound, the darkest, and the most silent of solitudes.

The solar system seems to us very vast, the abyss which separates our world from Mars, Jupiter, Saturn, and Neptune appears to us immense; relatively to the fixed stars, however, our whole system represents but an isolated family immediately surrounding us: a sphere as vast as the whole solar system would be reduced to the size of a simple point if it were transported to the distance of the nearest star. The space which extends between the solar system and the stars, and which separates the stars from each other, appears to be entirely void of visible matter, with the exception of nebulous fragments, cometary or meteoric, which circulate here and there in the immense voids. Nine thousand two hundred and fifty systems like ours (bounded by Neptune), would be contained in the space which isolates us from the nearest star!

If a terrible explosion occurred in this star, and if the sound could traverse the void which separates it from us, this sound would take more than three millions of years to reach us.

It is marvelous that we can perceive the stars at such a distance. What an admirable transparency in these immense spaces to permit the light to pass, without being wasted, to thousands of billions of miles! Around us, in the thick air which envelops us, the mountains are already darkened and difficult to see at seventy miles; the least fog hides from us objects on the horizon. What must be the tenuity, the rarefaction, the extreme transparency of the ethereal medium which fills the celestial spaces!

Let us suppose ourselves, then, on the sun nearest to ours. From there our dazzling furnace is already lost like a little star, hardly recognizable among the constellations: earth, planets, comets sail in the invisible. We are in a new system. If we thus approach each star we find a sun, while all the other suns of space are reduced to the rank of stars. Strange reality!—the normal state of the universe is night. What we call day only exists for us because we are near a star.

The immense distance which isolates us from all the stars reduces them to the state of motionless lights apparently fixed on the vault of the firmament. All human eyes, since humanity freed its wings from the animal chrysalis, all minds since the minds have been, have contemplated these distant stars lost in the ethereal depths; our ancestors of Central Asia, the Chaldeans of Babylon, the Egyptians of the Pyramids, the Argonauts of the Golden Fleece, the Hebrews sung by Job, the Greeks sung by Homer, the Romans sung by Virgil—all these earthly eyes, for so long dull and closed, have been fixed from age to age on these eyes of the sky, always open, animated, and living. Terrestrial generations, nations and their glories, thrones and altars have vanished: the sky of Homer is always there. Is it astonishing that the heavens were contemplated, loved, venerated, questioned, and admired even before anything was known of their true beauties and their unfathomable grandeur?

Better than the spectacle of the sea calm or agitated, grander than the spectacle of mountains adorned with forests or crowned with perpetual snow, the spectacle of the sky attracts us, envelops us, speaks to us of the infinite, gives us the dizziness of the abyss; for, more than any other, it seizes the contemplative mind and appeals to it, being the truth, the infinite, the eternal, the all. Writers who know nothing of the true poetry of modern science have supposed that the perception of the sublime is born of ignorance, and that to admire it is necessary not to know. This is assuredly a strange error, and the best proof of it is found in the captivating charm and the passionate admiration which divine science now inspires, not in some rare minds only, but in thousands of intellects, in a hundred thousand readers impassioned in the search for truth, surprised, almost ashamed at having lived in ignorance of and indifference to these splendid realities, anxious to incessantly enlarge their conception of things eternal, and feeling admiration increasing in their dazzled minds in proportion as they penetrate further into Infinitude. What was the universe of Moses, of Job, of Hesiod, or of Cicero, compared to ours! Search through all the religious mysteries, in all the surprises of art, painting, music, the theatre, or romance, search for an intellectual contemplation which produces in the mind the impression of truth, of grandeur, of the sublime, like astronomical contemplation! The smallest shooting star puts to us a question which it is difficult not to hear; it seems to say to us, What are we in the universe? The comet opens its wings to carry us into the profundities of space: the star which shines in the depths of the heavens shows us a distant sun surrounded with unknown humanities who warm themselves in his rays. Wonderful, immense, fantastic spectacles, they charm by their captivating beauty and transport into the majesty of the unfathomable the man who permits himself to soar and wing his flight to Infinitude.

Nel ciel che più della sua luce prende

Fu’ io, e vidi cose che ridire

Né sa, né può qual di lassù discende.

“I have ascended into the heavens, which receive most of His light, and I have seen things which he who descends from on high knows not, neither can repeat,” wrote Dante in the first canto of his poem on “Paradise.” Let us, like him, rise toward the celestial heights, no longer on the trembling wings of faith, but on the stronger wings of science. What the stars would teach us is incomparably more beautiful, more marvelous, and more splendid than anything we can dream of.

Chart of the Northern Constellations
Showing the principal Stars of the first five magnitudes visible to the naked eye

Among the innumerable army of stars which sparkle in the infinite night, the gaze is especially arrested by the most brilliant lights and by certain groups which vaguely present a mysterious bond between the worlds of space. These groups have been noticed at all epochs, even among the rudest races of men, and from the earliest ages of humanity they have received names, usually derived from the organic kingdom, which give a fantastic life to the solitude and the silence of the skies. Thus were early distinguished the seven stars of the North, or the Chariot, of which Homer speaks; the Pleiades, or the “Poussinière”; the giant Orion; the Hyades in the head of Taurus; Boötes, near the Chariot or Great Bear. These five groups were already named more than 3,000 years ago, and so were the brightest stars of the sky, Sirius and Arcturus, etc.

The epoch of the formation of the constellations is unknown, but we know that they were established successively. The centaur Chiron, Jason’s tutor, has the reputation of having first divided the sky on the sphere of the Argonauts. But this is mythology; and, besides, Job lived before the epoch at which Chiron is supposed to have flourished, and Job had already spoken of Orion, the Pleiades, and the Hyades 3,000 years ago. Homer also speaks of these constellations in describing the famous shield of Vulcan. “On its surface,” says he, “Vulcan, with a divine intelligence traces a thousand varied pictures. He represents the earth, the heavens, the sea, the indefatigable sun, the moon at its full, and all the stars which wreath the sky: the Pleiades, the Hyades, the brilliant Orion, the Bear, which they also call the Chariot, and which revolves round the pole; this is the only constellation which does not dip into the ocean waves” (Iliad, chapter xviii.).

Several theologians have affirmed that it was Adam himself, in the terrestrial paradise, who gave their names to the stars; the historian Josephus assures us that it was not Adam, but his son Seth, and that in any case astronomy was cultivated long before the Deluge. This nobility is sufficient for us.

Attentive observation of the sky also noticed from the beginning the beautiful stars Vega of the Lyre, Capella of Auriga, Procyon of the Little Dog, Antares of the Scorpion, Altair of the Eagle, Spica of the Virgin, the Twins, the Chair of Cassiopeia, the Cross of the White Swan, stretched in the midst of the Milky Way. Although noticed at the epoch of Hesiod and Homer, these constellations and stars were probably not yet named, because doubtless men had not yet felt the necessity of registering them for any application to the calendar, to navigation, or to voyages.[7]

At the epoch when the maritime power of the Phœnicians was at its apogee, about 3,000 years ago, or twelve centuries before our era, it was the star β of the Little Bear which was the nearest bright star to the pole, and the skilful navigators of Tyre and Sidon (O purpled kings of former times! what remains of your pride?) had recognized the seven stars of the Little Bear, which they named the Tail of the Dog, Cynosura; they guided themselves by the pivot of the diurnal motion, and during several centuries they surpassed in precision all the mariners of the Mediterranean. The Dog has given place to a Bear, doubtless on account of the resemblance of the configuration of these seven stars to the seven of the Great Bear, but the tail remains long and curled up, in spite of the nature of the new animal.

Thus the stars of the North at first served as points of reference for the first men who dared to venture on the seas. But they served at the same time as guides on the mainland for the nomadic tribes who carried their tents from country to country. In the midst of savage nature, the first warriors themselves had nothing but the Little Bear to guide their steps.

Imperceptibly, successively, the constellations were formed. Some groups resemble the names which they still bear, and suggested their denomination to the men of ancient times, who lived in the midst of nature and sought everywhere for relations with their daily observations. The Chariot; the Chair; the Three Kings, also named the Rake; Jacob’s Staff and the Belt of Orion; the Pleiades, or the Hen and Chickens; the Arrow (Sagitta); the Crown; the Triangle; the Twins; the Dragon; the Serpent; and even the Bull, the Swan, the Giant Orion, the Dolphin, the Fishes, the Lion, Water and Aquarius (the Water-bearer), etc., have given rise to the analogy. These resemblances are sometimes vague and far-fetched, like those we find in the clouds; but it appears much more natural to admit this origin than to suppose, with the classic authors, that these names were suggested by the concordance between the seasons or the labors of the fields and the presence of the stars above the horizon. That the name of the Balance (Libra) was given to the constellation of the equinox because then the days are equal, seems to us more than questionable; that Cancer (the Crab) signifies that the sun goes back to the solstice, and that the Lion has for its object to symbolize the heat of summer, and Aquarius the rain and inundations, appears to us no less imaginary. However, they have also had other origins. Thus, the Great Dog Sirius certainly announced the rising of the Nile and the dog-days (which remain in our calendar as a fine type of anachronism). Poetry, gratitude, the deification of heroes, mythology, afterward transferred to the sky the names of personages and sovereigns—Hercules, Perseus, Andromeda, Cepheus, Cassiopeia, Pegasus; later, in the Roman epoch, they added the Hair of Berenice and Antinous; later still, in modern times, they added the Southern Cross, the Indian, the Sculptor’s Workshop (Cœlum), the Lynx, the Giraffe (Camelopardus), the Greyhounds (Canes Venatici), the Shield of Sobieski, and the little Fox (Vulpecula). They even placed in the sky a Mountain, an Oak, a Peacock, a Swordfish, a Goose, a Cat, a Crane, a Lizard, and a Fly, for which there was no necessity.

This is not the place to describe and draw in detail all these constellations, with their more or less strange figures. The important point for us here is to form a general idea.

The sky remains divided into provinces, each of which continues to bear the name of the primitive constellation. But it is important to understand that the positions of the stars themselves, as we see them, are not absolute, and that the different configurations which they may show us are only a matter of perspective. We already know that the sky is not a concave sphere on which brilliant nails could be attached; that it is not a species of vault; that an immense infinite void envelops the earth on all sides, in all directions. We know also that the stars, the suns of space, are scattered at all distances in the vast immensity. When, therefore, we remark in the sky several stars near each other, that does not imply that these stars form the same constellation, that they are on the same plane, and at an equal distance from the earth. By no means; the arrangement which they assume to our eyes is but an appearance caused by the position of the earth relatively to them. This is a mere matter of perspective. If we could leave our world, and transport ourselves to a point in space sufficiently distant, we should see a variation in the apparent arrangement of the stars so much the greater as our station of observation were more distant from where we are at present. A moment’s reflection is sufficient to convince us of this fact, and save us from insisting further on this point.

Once these illusions are appreciated at their true value, we can begin the description of the figures with which the ancient mythology has constellated the sphere. A knowledge of the constellations is necessary for the observation of the heavens and for the researches which a love of the sciences and curiosity may suggest; without it we find ourselves in an unknown country, of which the geography has not been made, and where it would be impossible to know our exact position. Let us make, then, this celestial geography; let us see how to find our way, in order to read readily in the great book of the heavens.

There is a constellation which everybody knows; for greater simplicity we will begin with it. It will serve us well as a point of departure from which to go to the others, and as a point of reference to find its companions. This constellation is the Great Bear, which has also been named the Chariot of David.

It may well boast of being celebrated. If, notwithstanding its universal notoriety, some of our readers have not yet made its acquaintance, the following is a description by which they may recognize it.

Fig. 2

Turn yourself toward the north—that is to say, opposite to the point where the sun is found at noon. Whatever may be the season of the year, the day of the month, or the hour of the night, you will always see there a large constellation formed of seven fine stars, of which four are in a quadrilateral, and three at an angle with one side; all are arranged as we see in Fig. 2.

You have all seen it, have you not? It never sets. Night and day it watches above the northern horizon, turning slowly in twenty-four hours round a star of which we shall speak directly. In the figure of the Great Bear, the three stars of the extremity form the tail, and the four in the quadrilateral lie in the body. In the Chariot, the four stars of the quadrilateral form the wheels, and the other three the pole, the horses, or the oxen. Above the second of these latter stars, ζ, good sight distinguishes quite a little star named Alcor, which is also called the Cavalier. It serves to test the power of the sight. Each star is designated by a letter of the Greek alphabet: α and β mark the first two stars of the quadrilateral, γ and δ the two following, ε, ζ, η, the three of the pole. Arabic names have also been given to these stars, which we will pass in silence, because they are generally obsolete, with the exception, however, of that of the second horse—Mizar. With reference to the Greek letters, many persons think that it would be preferable to suppress them and to replace them by numbers. But this would be impossible in the practice of astronomy; and, moreover, inevitable confusion would result, on account of the numbers which the stars bear in the catalogues.

The Latins gave to plowing oxen the name of triones; instead of speaking of a chariot and three oxen, they came to call them the seven oxen (septemtriones). From this is derived the word septentrion, and there are now doubtless but few persons who, in writing this word, know that they are speaking of seven oxen. It is the same, however, with many other words. Who remembers, for example, in using the word tragedy, that he speaks of a song of a goat: tragôs-ode?

Let us go back to Fig. 2. If we draw a straight line through the two stars marked α and β which form the right side of the square, and produce it beyond α to a distance equal to five times that from β to α, or to a distance equaling that from α to the end of the tail, η, we find a star a little less brilliant than at the extremity of a figure similar to the Great Bear, but smaller and pointing in the opposite direction. This is the Little Bear, or the Little Chariot, also formed of seven stars. The star to which our line leads us—that which is at the tip of the tail of the Little Bear, or at the end of the pole of the Little Chariot—is the polar star.

Fig. 3

The polar star enjoys a certain fame, like all persons who are distinguished from the common, because, among all the bodies which scintillate in the starry night, it alone remains motionless in the heavens. At any moment of the year, by day or by night, when you observe the sky, you will always find it. All the other stars, on the contrary, turn in twenty-four hours round it, taken as the centre of this immense vortex. The pole star remains motionless at the pole of the world, from whence it serves as a fixed point to navigators on the trackless ocean, as well as to travelers in the unexplored desert.

Fig. 4

In looking at the pole star, motionless in the midst of the northern region of the sky, we have the south behind us, the east to the right, the west to the left. All the stars turn round the pole star in a direction contrary to that of the hands of a watch; they should, then, be recognized according to their mutual relations rather than by reference to the cardinal points.

On the other side of the pole star, with reference to the Great Bear, is found another constellation which we can also recognize at once. If from the middle star, δ, we draw a line to the pole, and produce this line by the same distance (see [Fig. 3]), we arrive at Cassiopeia, formed of five principal stars arranged somewhat like the strokes of the letter M. The little star χ, which completes the square, gives the constellation the form of a chair. This group assumes all possible positions in turning round the pole; it is found sometimes above, sometimes below, sometimes to the right, and sometimes to the left; but it is always easily recognized, for, like the preceding group, it never sets, and is always opposite to the Great Bear. The pole star is the axle round which both these constellations turn.

Fig. 5 Fig. 6

If, now, we draw from the stars α and δ of the Great Bear two lines through the pole, and produce them beyond Cassiopeia, we come to the Square of Pegasus (see [Fig. 4]), which shows a line of three stars somewhat similar to the tail of the Great Bear. These three stars belong to Andromeda, and lead to another constellation, Perseus. The last star of the Square of Pegasus is, as we see, the first (α) of Andromeda; the three others are named γ, α, and β. To the north of β of Andromeda is found, near a little star, ν, an oblong nebula, which can be distinguished with the naked eye. In Perseus, α, the brightest—on the prolongation of the three principal stars of Andromeda—appears between two others less brilliant, which form with it a concave arc very easy to distinguish. This arc serves us for a new alignment. Producing it in the direction of δ, we find a very brilliant star of the first magnitude; this is Capella (the Goat). Forming a right angle with this prolongation toward the south we come to the Pleiades (Fig. 5). Not far from that is a variable star, Algol, or the Head of Medusa, which varies from the second to the fourth magnitude[8] in 2 days, 20 hours, 48 minutes, 51 seconds. We may add, that in this region the star γ of Andromeda is one of the most beautiful double stars (it is even triple).

Fig. 7 Fig. 8

If, now, we produce beyond the Square of Pegasus (Fig. 6) the curved line of Andromeda, we reach the Milky Way, and we meet in these parts Cygnus, like a cross; the Lyre, where Vega shines (Fig. 7); the Eagle, and Altair (not Atair, as it is sometimes written) with two companions (Fig. 8).

Such are the principal constellations visible in the circumpolar regions on one side; we shall make a fuller acquaintance with them directly. While we are tracing the lines of reference let us still have a little patience and finish our summary review of this part of the sky.

Fig. 9

Look now at the side opposite to that of which we have just spoken. Let us return to the Great Bear. Producing the tail along its curve, we find at some distance from that a star of the first magnitude, Arcturus (Fig. 9), or α of Boötes. A little circle of stars which we see to the left of Boötes constitutes the Northern Crown (Corona Borealis). In the month of May, 1866, there was seen shining there a fine star, the brightness of which lasted only fifteen days. The constellation of Boötes is traced in the form of a pentagon. The stars which compose it are of the third magnitude, with the exception of Arcturus, which is of the first. This is one of the nearest to the earth; at least, it is one of a small number whose distance has been measured. It shines with a beautiful golden yellow color. The star ε, which we see above it, is double—that is to say, the telescope resolves it into two distinct stars, one yellow, the other blue.

Fig. 10.

This technical description is far from the poetry of Nature; but it is especially important here to be clear and precise. Let us suppose ourselves, however, under the starry vault on a beautiful summer’s night, splendid and silent, and let us consider that each of these points which we seek to recognize is a world, or rather a system of worlds. Look at this equilateral triangle (Fig 10); it permits us to cast our eyes successively on three important suns: Vega of the Lyre, Arcturus of Boötes, and the pole star, which watches above the solitudes of our mysterious North Pole. Many martyrs of science have died looking at it! In twelve thousand years our descendants will see the Lyre at the pole, ruling the harmony of the heavens.

The stars which are near the pole, and which have for that reason received the name of circumpolar stars, are distributed in the groups which have just been indicated. I earnestly invite my readers to profit by fine evenings, and try to find for themselves these constellations in the sky.

We have here the principal stars and constellations of the Northern Hemisphere, the North Pole being at the centre of the circle. We come now in the order of our description to the twelve constellations of the zodiacal belt, which makes the circuit of the sky, inclined at 23° to the Equator, and of which the ecliptic, the apparent path of the sun, forms the centre line.

The name of zodiac, given to the zone of stars which the sun traverses during the course of the year, comes from ζώδια, animals, an etymology which is due to the species of figures traced on this belt of stars. Animals, in fact, predominate in these figures. The entire circumference of the sky has been divided into twelve parts, which have been named the twelve signs of the zodiac; our ancestors called them the “houses of the sun,” or “the monthly abodes of Apollo,” because the day star visits them each month, and returns every spring to the beginning of the zodiacal city. Two memorable Latin verses of the poet Ausonius present to us these twelve signs in the order in which the sun travels through them, and this still appears the easiest method of learning them by heart.

Sunt Aries, Taurus, Gemini, Cancer, Leo, Virgo,

Libraque, Scorpius, Arciteneus, Caper, Amphora, Pisces;

or, in English, the Ram ♈︎, the Bull ♉︎, the Twins ♊︎, the Crab ♋︎, the Lion ♌︎, the Virgin ♍︎, the Balance ♎︎, the Scorpion ♏︎, the Archer ♐︎, Capricornus ♑︎, Aquarius ♒︎, and the Fishes ♓︎. The signs placed beside these names are a vestige of the primitive hieroglyphics which described them: ♈︎ represents the horns of the Ram, ♉︎ the head of the Bull; ♒︎ is a stream of water, etc.

If we now know our northern sky, if its most important stars are sufficiently noted down in our mind, with the reciprocal relations which they preserve among themselves, we have no more confusion to fear, and it will be easy to recognize the zodiacal constellations. This zone may be of use to us as a line of division between the north and the south. Here is a description of it:

The Ram, which, moving in front of the herd, and regulating, so to say, the march, opens the series. This constellation has in itself nothing remarkable; the brightness of its stars indicates the base of one of the horns of the leader of the sheep; it is but of the second magnitude. After the Ram comes the Bull. Admire on a fine winter’s night the charming Pleiades which scintillate in the ether; not far from them shines a fine red star—this is the eye of the Bull—Aldebaran, a star of the first magnitude and one of the finest of our sky. We now arrive at the Twins, whose heads are marked by two fine stars of the second magnitude, situated a little above a star of the first magnitude—Procyon, or the Little Dog; Cancer, or the Crab, a constellation very little conspicuous (its most visible stars are but of the fourth magnitude, and occupy the body of the animal); the Lion, a fine constellation, marked by a star of the first magnitude, Regulus, by one of the second, β, and by several others of the second and third magnitudes arranged in a trapezium; the Virgin, indicated by a very brilliant star of the first magnitude; Spica, situated in the neighborhood of a star, also of the first magnitude, Arcturus, which is found on the prolongation of the tail of the Great Bear; the Balance (Libra), indicated by two stars of the second magnitude, which would exactly resemble the Twins if they were nearer to each other; the Scorpion, a remarkable constellation; a star of the first magnitude, of a fine red color, marks the Heart (Antares), in the middle of two stars of the third magnitude, above which are three bright stars arranged in a diadem; Sagittarius, the Archer, of which the arrow, indicated by three stars of the second and third magnitudes, is pointed toward the tail of the Scorpion; Capricornus, a constellation not conspicuous, which is recognized by two stars of the third magnitude very near each other, and representing the base of the horns of the hieroglyphic animal; Aquarius, indicated by three stars of the third magnitude arranged in a triangle, of which the most northern occupies a point on the equator; Pisces, the Fishes, composed of stars, barely conspicuous, of the third to fourth magnitudes, situated to the south of a large and magnificent quadrilateral—the Square of Pegasus—of which we have already spoken.