A MODERN ZOROASTRIAN.

A MODERN ZOROASTRIAN.

A MODERN ZOROASTRIAN

BY
S. LAING,
AUTHOR OF
“MODERN SCIENCE AND MODERN THOUGHT,” “PROBLEMS OF THE FUTURE,”
“HUMAN ORIGINS.”

Eighth Thousand.

LONDON: CHAPMAN AND HALL, Ld.
1893.

CHARLES DICKENS AND EVANS,
CRYSTAL PALACE PRESS.

PREFACE TO NEW EDITION.

From some of the criticisms on the First Edition of this work I fear that the distinction I endeavoured to draw between the use of the term “polarity” in the inorganic and in the spiritual worlds has not been made sufficiently clear. I stated in the Introduction “That while the principle of polarity pervades both worlds, I am far from assuming that the laws under which it acts are identical; and that virtue and vice, pain and pleasure, are products of the same mathematical laws as regulate the attractions and repulsions of molecules and atoms.” But this warning has been apparently overlooked by some readers who have assumed that instead of analogy I meant identity, and that it was a mistake to use the same word “polarity” for phenomena so essentially distinct as those of the material and the spiritual worlds.

Thus my “guide, philosopher, and friend,” Professor Huxley, for whose authority I have the highest respect, observed in a recent article, that he had long ago acquired a habit, if he came across the word polarity applied to anything but magnetism and electricity, of throwing down the book and reading no farther. I must confess that I felt a little disconcerted when I read this passage; but I was soon consoled, for, in a month or two afterwards, I came across another passage in the same Review which said, “However revolting may be the accumulation of misery at the negative pole of Society, in contrast with that of monstrous wealth at the positive pole, this state of things must abide and grow continuously worse, as long as Istar (the dual Goddess of the Babylonians) holds her way unchecked.”

Surely, I thought, here is a case in which the Professor must have thrown down the Review when he came to these words: but when I came to the end, I found that it was not the Review, but the pen, which must have been thrown down, for the article is signed “T. Huxley.” Can there be a more conclusive proof that there are a vast variety of facts outside of magnetism and electricity, connected by an underlying idea, which inevitably suggests analogy to them, and which can be most conveniently expressed by the word “polarity”? Words after all are only coins to facilitate the interchange of ideas, and the best word is that which serves the purpose most clearly and concisely. Thus instead of using a waggon load of copper, or the verbiage of a conveyancer’s deed, to express the ideas comprised in such words as “theism,” “pantheism,” or “agnosticism,” we coin them for general use, as Huxley did the word “agnosticism,” in order to convey our meaning.

Polarity is such a word. It sums up what Emerson says in his Essay on Compensation: “Polarity, or action and reaction, we meet in every part of Nature; in darkness and light; in the ebb and flow of waters; in male and female; in the inspiration and expiration of plants and animals; in the undulations of fluids and of sound; in the centripetal and centrifugal gravity; in electricity, galvanism, and chemical affinity. Superinduce Magnetism at one end of a needle, the opposite Magnetism takes place at the other end. If the South attracts, the North repels. An inevitable dualism besets nature, so that each thing is a half, and suggests another to make it whole: as spirit, matter; man, woman; odd, even; subjective, objective; in, out; upper, under; motion, rest; yea, nay.”

These, by whatever name we like to call them, are facts and not fancies, and facts which enter largely into all questions, whether of science, philosophy, religion, or practical policy. Every one who wishes to keep at all abreast with modern culture, ought to have some general knowledge of the ideas and principles which underlie them and which are embraced in the comprehensive word “polarity.” My object in this book has been to assist the reader, who is not a specialist, in arriving at some general understanding of the subjects treated of, and I may hope, in awakening such an interest in them as may induce him to prosecute further researches. If I succeed in this, my object will have been attained.

PREFACE.

The reception given to my former work, on ‘Modern Science and Modern Thought,’ has induced me to write this further one. I refer not so much to the reviews of professional critics, though as a rule nothing could be more courteous and candid, but rather to the letters I have received from readers of various age, sex, and condition, saying that I had assisted them in understanding much interesting matter which had previously been a sealed book to them.

If I am good for anything, it is for a certain faculty of lucid condensation, and I have thought that I might apply this to some of the less-known branches of modern science, such as the new chemistry and physiology, as well as, in my first work, to the more familiar subjects of astronomy and geology; while at the same time I might extend it to some of the more obvious problems of religion, morals, metaphysics, and practical life, which force themselves, more and more every day, on the attention of intelligent thinkers.

As in the former work the scientific speculations were linked together by the leading idea of the universality of law, so, in this, unity is given to them by the all-pervading principle of polarity, which manifests itself everywhere as the fundamental condition of the material and spiritual universe.

For the scientific portion of the work I am indebted to the most approved authorities, such as Darwin, Huxley, Haeckel, and Professor Cooke’s volume on the New Chemistry in the International Scientific Series. For the religious and philosophical speculations I am myself responsible; for, although I have derived the greatest possible pleasure and profit from Herbert Spencer’s writings, I had arrived at my principal conclusions independently before I had read any of his works. I can only hope that I may have succeeded in presenting a good many abstruse questions in a popular form, intelligible to the average mind of ordinary readers, and calculated, if it teaches nothing else, to teach them a practical philosophy which inculcates tolerance and charity, and assists them in finding

Sermons in stones and good in everything.

CONTENTS.

A MODERN ZOROASTRIAN.

CHAPTER I.
INTRODUCTORY.

Experiment with magnet—Principle of polarity—Applies universally—Analogies in spiritual world—Zoroastrian religion—Changes in modern environment—Require corresponding changes in religions and philosophies.

Scatter a heap of iron filings on a plate of glass; bring near it a magnet, and tap the glass gently, and you will see the filings arrange themselves in regular forms.

If one pole only of the magnet is brought near the glass the filings arrange themselves in lines radiating from that pole.

Next lay the bar-magnet on the glass so that the filings are influenced by both poles; they will arrange themselves into a series of regular curves.

In other words, the Chaos of a confused heap of inert matter has become a Cosmos of harmonious arrangement assuming definite form in obedience to law.

As the old saying has it, that ‘every road leads to Rome,’ so this simple experiment leads up to a principle which underlies all existence knowable to human faculty—that of Polarity. Why do the iron filings arrange themselves in regular curves? Because they are magnetised by the influence of the larger magnet, and each little particle of iron is converted into a little magnet with two opposite poles attracting and repelling.

What is a magnet? It is a special manifestation of the more general principle of polarity, by which energy, when it passes from the passive or neutralised into the active state, does so under the condition of developing opposite and conflicting energies: no action without reaction, no positive without a negative, and, as we see it in the simplest form in our magnets, no North Pole without a South Pole—like ever repelling like and attracting unlike. The magnet, again, may be considered as a special form of electricity, for if we send an electric current through a coil of copper wire encircling a bar of soft iron, the bar is at once converted into a magnet; so that a magnet may be considered as the summing up, at two opposite extremities or poles, of the attractive and repulsive effects of electric currents circulating round it. But this electricity is itself subject to the law of polarity, whether developed by chemical action in the form of a current or electricity in motion, or by friction in the form of statical electricity of small quantity but high tension. In all cases a positive implies a negative; in all, like repels like and attracts unlike. Conversely, as polarity produces definite structure, so definite structure everywhere implies polarity.

The same principle prevails not only throughout the inorganic or world of matter, but throughout the organic or world of life, and specially throughout its highest manifestations in human life and character, and in the highest products of its evolution, in societies, religions, and philosophies. To show this by some familiar and striking examples is the main object of this book.

But here let me interpose a word of caution. I must avoid the error which vitiates Professor Drummond’s interesting work on ‘Natural Law in the Spiritual World,’ of confounding analogy and identity. Because the principle of polarity pervades alike the natural and spiritual worlds, I am far from assuming that the laws under which it acts are identical; and that virtue and vice, pain and pleasure, ugliness and beauty, are products of the same mathematical changes of sign and inverse squares or cubes of distances, as regulate the attractions and repulsions of molecules and atoms. All I say is, that the same pervading principle may be traced wherever human thought and human knowledge extend; that it is apparently, for some reason unknown to us, the essential condition of all existence within the sphere of that thought and that knowledge; and that what lies beyond it is the great unknown, behind the impenetrable veil which it is not given to mortals to uplift. In like manner, if I call myself ‘a modern Zoroastrian,’ it is not that I wish or expect to teach a new religion or revive an old one, to see Christian churches dedicated to Ormuzd, or right reverend bishops exchanging the apron and shovel-hat for the mitre and flowing robes of the ancient Magi; but simply this. All religions I take to be ‘working hypotheses,’ by which successive ages and races of men try to satisfy the aspirations and harmonise the knowledge which in the course of evolution have come to be, for the time, their spiritual equipment. The best proof of any religion is, that it exists—i.e. that it is part of the same evolution, and that on the whole it works well, i.e. is in tolerable harmony with its environment. When that environment changes, when loftier views of morality prevail, when knowledge is increased and the domain of science everywhere extends its frontier, religions must change with it if they are to remain good working, and not become unworkable and unbelievable hypotheses.

Now of all the religious hypotheses which remain workable in the present state of human knowledge, that seems to me the best which frankly recognises the existence of this dual law, or law of polarity, as the fundamental condition of the universe, and, personifying the good principle under the name of Ormuzd, and the evil one under that of Ahriman, looks with earnest but silent and unspoken reverence on the great unknown beyond, which may, in some way incomprehensible to mortals, reconcile the two opposites, and give the final victory to the good.

Oh! yet we hope that somehow good

Will be the final goal of ill.

So sings the poet of the nineteenth century: so, if we understand his doctrine rightly, taught the Bactrian sage, Zoroaster, some forty centuries earlier.

This, and this alone, seems to me to afford a working hypothesis which is based on fact, can be brought into harmony with the existing environment, and embraces, in a wider synthesis, all that is good in other philosophies and religions.

When I talk of our new environment, it requires one who, like the author, has lived more than the Scriptural threescore and ten years, and has, so to speak, one foot on the past and one on the present, to realise how enormous is the change which a single generation has made in the whole spiritual surroundings of a civilised man of the nineteenth century. When I was a student at Cambridge, little more than fifty years ago, Astronomy was the only branch of natural science which could be said to be definitely brought within the domain of natural law. And that only as regards the law of gravity, and the motions of the heavenly bodies, for little or nothing was known as to their constitution. Geology was just beginning the series of conquests by which time and the order and succession of life on the earth have been annexed by science as completely as space by astronomy; and theories of cataclysms, universal deluges, and special recent creations of animals and man, still held their ground, and were quoted as proofs of a universe maintained by constant supernatural interference.

And when I say that space had been annexed to science by astronomy, it was really only that half of space which extends from the standpoint of the human senses in the direction of the infinitely great. The other equally important half which extends downwards to the infinitely small was unknown, or the subject only of the vaguest conjectures.

Chemistry was, to a great extent, an empirical science, and molecules and atoms were at best guesses at truth, or rather convenient mathematical abstractions with no more actual reality than the symbols of the differential calculus. The real causes and laws of heat, light, and electricity, were as little known as those of molecular action and of chemical affinity. The great laws of the indestructibility of matter, the correlation of forces, and the conservation of energy, were unknown, or only just beginning to be foreshadowed. As regards life, protoplasm was a word unheard of; scientific biology, zoology, and botany were in their infancy; and the gradual building up of all living matter from a speck of protoplasm, through a primitive cell, was not even suspected. Above all, the works of Darwin had not been published, and evolution had not become the general law of modern thought; nor had the discovery of the antiquity of man, and of his slow development upwards from the rudest origins, shattered into fragments established beliefs as to his recent miraculous creation.

Science and miracle have been fighting out their battle during the last fifty years along the whole line, and science has been at every point victorious. Miracle, in the sense in which our fathers believed in it, has been not only repulsed, but annihilated so completely, that really little remains but to bury the dead.

The result of these discoveries has been to make a greater change in the spiritual environment of a single generation than would be made in their physical environment if the glacial period suddenly returned and buried Northern Europe under polar ice. The change is certainly greater in the last fifty years than it had been in the previous five hundred, and in many respects greater than in the previous five thousand.

It may be sufficient to glance shortly at the equally great corresponding changes which this period has witnessed in the practical conditions of life and of society. If astronomy and geology have extended the dominion of the mind over space and time, steamers, railways, and the electric telegraph have gained the mastery over them for practical purposes. Commerce and emigration have assumed international proportions, and India, Australia, and America are nearer to us, and connected with us by closer ties, than Scotland was to England in my schoolboy days. Education and a cheap press have even in a greater degree revolutionised society, and knowledge, reaching the masses, has carried with it power, so that democracy and free-thought are, whether for good or evil, everywhere in the ascendant, and old privileges and traditions are everywhere decaying.

With such a great change of environment it is evident that many of the old creeds, institutions, and other organisms, adapted to old conditions, must have become as obsolete as a schoolboy’s jacket would be as the comfortable habiliment of a grown-up man. But as a lobster which has cast its shell does not feel at ease until it has grown a new one, so thinking men of the present day are driven to devise, to a great extent each for themselves, some larger theory which may serve them as a ‘working hypothesis’ with which to go through life, and bring the ineradicable aspirations and emotions of their nature into some tolerable harmony with existing facts.

To me, as one of those thinking units, this theory, of what for want of a better name I call ‘Zoroastrianism,’ has approved itself as a good working theory, which reconciles more intellectual and moral difficulties, and affords a better guide in conduct and practical life than any other; and, in a word, enables me to reduce my own individual Chaos into some sort of an intelligible and ordered Cosmos. I feel moved, therefore, to preach through the press my little sermon upon it, for the benefit of those whom it may concern, feeling assured that the process of evolution, by which

The old order changes, giving place to new,

can best be assisted by the honest and unbiassed expression of the results of individual thought and experience on the part of any one of those units whose aggregates form the complicated organisms of religions and philosophies, of societies and of humanity.

CHAPTER II.
POLARITY IN MATTER—MOLECULES AND ATOMS.

Matter consists of molecules—Nature of molecules—Laws of their action in gases—Law of Avogadro—Molecules composed of atoms—Proved by composition of water—Combinations of atoms—Elementary substances—Qualities of matter depend on atoms—Dimensions and velocities of molecules and atoms—These are ascertained facts, not theories.

If in building a house that is to stand when the rains fall and the winds blow, it is requisite to go down to the solid rock for a foundation, so much the more is it necessary in building up a theory to begin at the beginning and give it a solid groundwork. Nine-tenths of the fallacies current in the world arise from the haste with which people rush to conclusions on insufficient premises. Take, for instance, any of the political questions of the day, such as the Irish question: how many of those who express confident opinions, and get angry and excited on one side or the other, could answer any of the preliminary questions which are the indispensable conditions of any rational judgment? How many marks would they get for an examination paper which asked what was the population of Ireland; what proportion of that population was agricultural; what proportion of that agricultural population consisted of holders of small tenements; what was the scale of rents compared with that for small holdings in other countries; how much of that rent was levied on them for their own improvements; and other similar questions which lie at the root of the matter? In how many cases would it be found that the whole superstructure of their confident and passionate theories about the Irish difficulty was based on no more solid foundation than their like or dislike of a particular statesman or of a particular party?

I propose therefore to begin at the beginning, and, taking the simplest case, that of dead or inorganic matter, show how the material universe is built up by the operation of the all-pervading law of polarity. What does matter consist of? Of molecules, and molecules are made up of atoms, and these are held together or parted, and built up into the various forms of the material universe, primarily by polar forces.

Let me endeavour to make this intelligible to the intelligent but unscientific reader. Suppose the Pyramid of Cheops shown for the first time to a giant whose eye was on such a scale that he could just discern it as a separate object. He might make all sorts of ingenious conjectures as to its nature, but if microscopes had been invented in Giant-land and he looked through one, he would find that it was built up, layer by layer, on a regular plan and in determinate lines and angles, by molecules, or what seemed to him almost infinitely small masses, of squared stone. For pyramid write crystal, and we may see by the human sense, aided by human instruments and human reason, a similar structure built up in the same way by minute particles. Or again, divide and subdivide our iron filings until we reach the limit of possible mechanical division discernible by the microscope; each one remains essentially a bar of iron, as capable of being magnetised, and showing the same qualities and behaviour under chemical tests as the original bar of iron from which the filings were taken. This carries us a long way down towards the infinitely small, for mechanical division and microscopic visibility can be carried down to magnitudes which are of the order of 1/100000th of an inch.

But this is only the first step; to understand our molecules we must ascertain whether they are infinitely divisible, and whether they are continuous, expanding by being spread out thinner and thinner like gold-beater’s skin: or are they separate bodies with intervals between them, like little planets forming one solar system and revolving in space by fixed laws. Ancient science guessed at the former solution and embodied it in the maxim ‘that nature abhors a vacuum’: modern science proves the latter.

In the first place bodies combine only in fixed proportions, which is a necessary consequence if they consist of definite indivisible particles, but inconceivable if the substance of each is indefinitely divisible. Thus water is formed in one way and one only: by uniting one volume or molecule of oxygen with two of hydrogen, and any excess of one or the other is left out and remains uncombined. But if the molecules could be divided into halves, quarters, and so on indefinitely, there can be no reason why their union should take place always in this one proportion and this only.

A still more conclusive proof is furnished by the behaviour of substances which exist in the form of gases. If a jar is filled with one gas, a second and third gas can be poured into it as readily as into a vacuum, the result being that the pressure on the sides of the jar is exactly equal to the sum of the separate pressures of each separate gas. This evidently means that the first gas does not occupy the whole space, but that its particles are like a battalion of soldiers in loose skirmishing order, with such intervals between each unit that a second and third battalion can be marched in and placed on the same ground, without disturbing the formation, and with the result only of increasing the intensity of the fire.

Now gas is matter as much as solids or liquids, and in the familiar instance of water we see that it is merely a question of more or less heat whether the same matter exists as ice, water, or steam. The number and nature of the molecules is not changed, only in the one case they are close to one another and solidly linked together; in the other, further removed and free to move about one another, though still held together as a mass by their mutual attractions; and in the third, still further apart, so that their mutual attraction is lost and they dart about, each with its own proper motion, bombarding the surface which contains them, and by the resultant of their impacts producing pressure.

In this latter and simpler form of gas the following laws are found to prevail universally for all substances. Under like conditions volumes vary directly as the temperature and inversely as the pressure. That is to say, the pressure which contains them remaining the same, equal volumes of air, steam, or any other substance in the state of gas, expand into twice the volume if the temperature is doubled, three times if it is tripled, and so on; contracting in the same way if the temperature is lowered. If on the other hand the temperature remains constant, the volume is reduced to one half or one third, if the pressure is doubled or tripled. From these laws the further grand generalisation has been arrived at, that all substances existing in the form of gas contain the same number of molecules in the same volume.

This, which is known as the Law of Avogadro, from the Italian chemist by whom it was first discovered, is the fundamental law of modern chemistry, and the key to all certain and scientific knowledge of the constitution of matter and of the domain of the infinitely small, just as much as the law of gravity is to action of matter in the mass, and the resulting conditions and motions of mechanics and astronomy.

This conclusion obviously follows from it, that difference of weight in different substances arises not from one having more molecules in the same volume than another, but from the molecules themselves being heavier. If we weigh a gallon or litre of hydrogen gas, which is the lightest known substance, and then weighing an equal volume of oxygen gas find that it is sixteen times heavier, we know for certain that the molecule or ultimate particle of oxygen is sixteen times heavier than that of hydrogen.

It is evident that in this way the molecules of all simple substances which can exist in the form of pure gas can be weighed, and their weight expressed in terms of the unit which is generally adopted, that of the molecule of the lightest known substance, hydrogen. But science, not content with this achievement, wants to know not the relative weight only, but the absolute dimensions, qualities, and motions of these little bodies; and whether, although they cannot be divided further by mechanical means, and while retaining the qualities of the substances they build up, they are really ultimate and indivisible particles or themselves composites.

Chemistry and electricity give a ready answer to this latter question. Molecules are composites of still smaller bodies, and to get back to the ultimate particle we must go to atoms. All chemical changes resolve themselves into the breaking up of molecules and rearrangement of their constituent atoms. If the opposite poles of a voltaic battery are inserted in a vessel containing water, molecules of water are broken up, bubbles of gas rise at each pole, and if these are collected, the gas at the positive pole is found to be oxygen, and that at the negative pole hydrogen. Nothing has been added or taken away, for the weight of the two gases evolved exactly equals that of the water which has disappeared. But the molecules of the water have been broken up, and their constituents reappear in totally different forms, for nothing can well be more unlike water than each of the two gases of which it is composed. That it is composed of them can be verified by the reverse experiment of mixing the two gases together in the same proportion of two volumes of hydrogen to one of oxygen as was produced by the decomposition of water, passing an electric spark through the vessel containing the mixture, when with a loud explosion the gases reunite, and water is formed in precisely the same quantity as produced the volumes of gas by its decomposition. Can the ultimate particles of these gases be further subdivided; can they, like those of water, be broken up and reappear in new forms? No; there is no known process by which an atom of oxygen can be made anything but oxygen, or an atom of hydrogen anything but hydrogen.

The only thing which is compound in the composition of oxygen is that its molecules consist of two atoms linked together. This appears from the fact that while the weight of oxygen, and therefore that of its molecules, is sixteen times greater than that of an equal volume of hydrogen, and therefore of hydrogen molecules, it combines with it in the proportion not of sixteen, but of eight to one. If, therefore, the molecule were identical with the atom of oxygen, we must admit that the atom could be halved, which is contrary to its definition as the ultimate indivisible particle of the substance oxygen. But if the oxygen molecule consists of two linked atoms, O—O, and the hydrogen molecule equally of two, H—H, as can be proved by other considerations, everything is explained by assuming that the molecule of water consists of two atoms of hydrogen linked to one of oxygen, or H₂O, and that when this molecule is broken up by electricity, its constituents resolve themselves into atoms, which recombine so as to form twice as many molecules of hydrogen, H—H, as of oxygen, O,—i.e. into two volumes of hydrogen gas to one of oxygen.

Taking the single hydrogen atom as the unit of weight as being the lightest known ponderable body, and calling this weight a microcrith, or standard of the smallest of this order of excessively small weights, this is equivalent to saying that the weight of an oxygen atom is equal to 16 microcriths, and as water is composed of one such atom plus two of hydrogen, the weight of its molecule ought to be 16 + 2 = 18, which is in fact the exact ratio in which the weight of a volume of steam, or water in the form of gas, is heavier than an equal volume of hydrogen.

This key unlocks the whole secret of the chemical changes and combinations by which matter assumes all the various forms known to us in the universe.

Thus oxygen enters into a great variety of combinations forming different substances, but always in the proportion which is either 16, or some multiple of 16, such as 32, 48, 64. That is, either 1, 2, 3, or 4 atoms of oxygen unite with other atoms to form the molecules from which these other substances are made.

One atom of oxygen weighing 16 microcriths combines, as we have seen, with two atoms of hydrogen weighing 2, to form a molecule of water weighing 18 mc. In like manner one atom of oxygen, 16 mc., combines with one of carbon, which weighs 12 mc., to form a molecule of carbonic oxide weighing 28 mc.; and two of oxygen, 32 mc., with one of carbon, 12 mc., to form a molecule of carbonic dioxide weighing 44 mc.

The same applies to all elementary substances. Thus hydrogen, two atoms of which combine with one of oxygen to form water, combines one atom to one with chlorine to form the molecule of hydrochloric acid, which weighs 36·5 mc., being the united weights of one atom of chlorine, 35·5 mc., and one of hydrogen, 1 mc. These, with hundreds of similar instances, are the results not of theories as to molecules and atoms, but of actual facts, ascertained by innumerable experiments made independently by careful observers over long periods of years, many of them dating back to the labours of the alchemists of the middle ages in pursuit of gold. The atomic theory is the child and not the parent of the facts, and is indeed nothing but the summary of the vast variety of experiments which led up to it, as Newton’s law of gravity is of the facts known to us with regard to the attractions and motions of matter in the mass. But as Newton’s law enables us to predict new facts, to calculate eclipses and the return of comets beforehand, and to compile nautical almanacs; so the new chemistry, based on the atomic theory, affords the same conclusive proof of its truth by enabling us in many cases to predict phenomena which are subsequently verified by experiment, and to infer beforehand what combinations are possible, and what will be their nature.

The actual existence, therefore, of molecules and atoms is as well-ascertained a fact, as that of cwts. and lbs., or of planets and stars, of solar systems and nebulæ.

The researches of chemists have succeeded in discovering about 70 substances, of which the same may be said as of the oxygen and hydrogen into which water is decomposed, viz. that they cannot be decomposed by any known process, and must therefore be considered as ultimate and elementary. Their atoms differ widely in size and weight: that of mercury, for instance, being 200 times heavier than that of hydrogen, and the weights varying from 1 mc. for the hydrogen atom, up to 240 for that of uranium. When we call them elementary substances, we merely mean that we know no means of decomposing them. It is possible that all of them may be compounds which we cannot take to pieces of some substratum of uniform matter, and it is remarkable that the weight of nearly all of these elementary atoms is some simple multiple of that of hydrogen, pointing to their being all combinations of one common substratum of matter; but this is merely conjecture, and in the present state of our knowledge we must assume these 66 or 71 ultimate particles or atoms to be the indivisible units out of which all the complicated puzzle of the material universe is put together. They are not all equally important to us. Of the 71 elementary substances enumerated in chemical treatises, 5 are doubtful, and 30 to 35 of the remainder are either known only to chemists in minute quantities, or exist in nature in small quantities, having no very material bearing upon man’s relation to matter. The most important are oxygen, hydrogen, nitrogen, and carbon. Oxygen diluted by nitrogen gives us the air we breathe, combined with hydrogen the water we drink, and with metals and other primitive bases the solid earth on which we tread. Carbon again is the great basis of organised matter and life, to which it leads up by a variety of complex combinations with oxygen, hydrogen, and nitrogen.

The qualities and relations of elementary atoms afford a subject of great interest, but of such vast extent that those who wish to understand it must be referred to professed works on modern chemistry. For the present purpose it is sufficient to say that the following conclusions are firmly established.

All the various forms of matter are composed of combinations of primitive atoms which form molecules, the molecules being neither more nor less than very small pieces of ordinary matter.

The qualities of this matter, or, what is the same thing, of its molecules, depend partly on the qualities of the atoms, which are something quite distinct from those of the molecules, and partly on their mode of aggregation into molecules, affecting the form, size, stability, and other attributes of the molecule.

All matter, down to the smallest atom, has definite weight and is indestructible. No man by taking thought can add the millionth of a milligramme to the weight of any substance, or make it either more or less than the sum of the weights of its component factors, any more than he can add a cubit to his stature. When Shelley sang of the cloud,

I change, but I cannot die,

he enunciated a scientific axiom of the first importance. Creation, in the sense of making something out of nothing, is a thing absolutely unknown and unknowable to us. If we say we make a ship or a steam-engine, we simply mean that we transform existing matter and existing energies into new combinations, which give results convenient for our purpose. So if we talk of making a world, our idea really is that if our powers and knowledge were indefinitely increased we might be able, given the atoms and energies with their laws of existence, to put them together so as to produce the desired results. But how the atoms and their inherent laws got there is a question as to which knowledge, or even conceivability, is impossible, for it altogether transcends human experience.

Before finally taking leave of atoms it may be well to state shortly that science, not content with having proved their existence and weighed them in terms of the lightest element, the hydrogen atom, has attempted, not without success, to solve the more difficult problem of their real dimensions, intervals, and velocities. This problem has been attacked by Clausius, Sir W. Thomson, Clerk Maxwell, and others, from various sides: from a comparison with the wave-lengths of light; with the tenuity of the thinnest films of soap-bubbles just before they burst, and when they are presumably reduced to a single layer of molecules; and from the kinetic theory of gases, involving the dimensions, paths, and velocities of elastic bodies, constantly colliding, and by their impacts producing the resulting pressure on the confining surface. All these methods involve such refined mathematical calculations that it is impossible to explain them popularly, but they all lead to nearly identical results, which involve figures so marvellous as to be almost incomprehensible. For instance, a cubic centimetre of air is calculated to contain 21 trillions of molecules—i.e. 21 times the cube of a million, or 21 followed by 18 ciphers; the average distance between each molecule equals 95 millionths of a millimetre, which is about 25 times smaller than the smallest magnitude visible under a microscope; the average velocity of each molecule is 447 metres per second; and the average number of impacts received by each molecule in a second is 4,700 millions.

CHAPTER III.
ETHER.

Ether proved by light—Light-waves—Elasticity of ether—Its universal diffusion—Influences molecules and atoms—Is influenced by them—Successive orders of the infinitely small—Illustrated by the differential and integral calculus—Explanation of this calculus—Theory of vortex rings.

Perhaps the best way to convey some idea of this order of magnitudes to the ordinary reader is to quote Sir W. Thomson’s illustration, that if we could suppose a cubic inch of water magnified to the size of the earth—i.e. to a sphere 24,000 miles in circumference—the dimensions of its ultimate particles, magnified on the same scale, or, as he expresses it, its degree of coarse-grainedness, would be something between the size of rifle-bullets and cricket-balls.

Extraordinary as these dimensions are, they are not more so than those at the opposite extremity of the scale, where the distance of stars and nebulæ has to be measured by the number of thousand years their light, travelling at the rate of 192,000 miles per second, takes to reach us. Infinitely small, however, as those dimensions appear to our original conceptions derived from our natural senses, they are certain and ascertained facts, if not as to the precise figures, yet beyond all doubt as to the orders of magnitude. In dealing with them also we are to a great extent on familiar ground. Molecules are nothing more nor less than small pieces of ordinary matter; and atoms are also matter, for they obey the law of gravity, have definite weights, and build up molecules as surely as molecules build up ordinary matter, and as squared stones build up pyramids.

But to understand the constitution of the material universe we must go a step further, part from the familiar world of sense, and deal with an all-pervading medium, which is at the same time matter and not matter, which lies outside the laws of gravity, and yet obeys other laws intelligible and calculable by us; of which it may be said we know it and we know it not. We call it Ether.

Ether is a medium assumed as a necessary consequence from the phenomena of light, heat, and electricity—primarily from those of light. Respecting light two facts are known to us with absolute certainty.

1st. It traverses space at the rate of 192,000 miles per second.

2nd. It is propagated not by particles actually travelling at this rate, but, like sound through air, by the transmission of waves.

The first fact is known from the difference of time at which eclipses of Jupiter’s satellites are seen according as the earth is at the point of its orbit nearest to or farthest from Jupiter—i.e. from the time light takes to traverse the diameter of the earth’s orbit, which is about 180 millions of miles; and this velocity of light is confirmed by direct experiments, as by noting the difference of time between seeing the flash and hearing the sound of a gun, which gives the velocity of light compared with the known velocity of sound.

The second fact is equally certain from the phenomena of what are called interferences, when the crest of one wave just overtakes the hollow of a preceding one, so that, if the two waves are of equal magnitude, the oscillations exactly neutralise one another, and two lights produce darkness. This is shown in a thousand different ways, and for all the different colours depending on different waves into which white light is analysed when passed through a prism. It is a certain result of wave-motion, and of wave-motion only, and therefore we know without a doubt that light is propagated by waves.

But waves imply a medium through which waveforms are transmitted, for waves are nothing but the rhythmic motion of something which rises and falls, or oscillates symmetrically about a mean position of rest, slowly or quickly according to the less or greater elasticity of the medium. The waves which run along a large and slack wire are large and slow, those along a small and tightly stretched wire are small and quick; and from the data we possess as to light, its velocity of transmission, its refraction when its waves pass from one medium into another of different density, and from the distance between the waves as shown by interference, it is easy to calculate the lengths and vibratory periods of the waves, and the elasticity of the medium through which such waves are transmitted.

The figures at which we arrive are truly extraordinary. The dimensions and rates of oscillations of the waves which produce the different colours of visible light have been measured and calculated with the greatest accuracy, and they are as follows:

Dimensions of Light-Waves.

The elasticity of this wonderful medium is even more extraordinary.

The rapidity with which wave-motion is transmitted depends, other things being equal, on the elasticity of the medium, which is proportional to the square of the velocity with which a wave travels through it. As the velocity of the sound-wave in air is about 1,100 feet in a second, and that of the light-wave about 192,000 miles in the same time, it follows that the velocity of the latter is about a million times greater than that of the former, and if the density of ether were the same as that of air, its elasticity must be about a million million times greater. But the elasticity is the same thing as the power of resisting compression, which in the case of air we know to be about 15 pounds to the square inch; so that the ether, if equally dense, would balance a pressure of 15 million million pounds to the square inch—that is, it would require a pressure of about 750 millions of tons to the square inch to condense ether to the density of air. On the other hand, its density, if any, must be so infinitesimally small that the earth moving through it in its orbit with a velocity of 1,100 miles a minute suffers no perceptible retardation.

Consider what this means. Air blowing at the rate of 100 miles an hour is a hurricane uprooting trees and levelling houses. If ether were as dense as air the resistance to the earth in passing through it would be 600 times that of going dead to windward in a tropical hurricane. But in point of fact there is no sensible resistance, for the earth and heavenly bodies move in their calculated paths according to the law of gravity exactly as they would do if they were moving in a vacuum. Even the comets, which consist of such excessively rare matter that when one of them got entangled among the satellites of Jupiter it did not affect their movements, are not retarded by the ether, or so slightly, that any retardation in the case of one or two of them is suspected rather than proved. But, if the ether has no weight, how can we call it material, weight being, as we have seen, the invariable test and measure of all matter down to the minutest atom? And yet how can we deny its existence when it is demonstrably necessary to account for undoubted facts revealed to us every day by the prism, the spectroscope, electricity, and chemical action, and deductions from these facts based on the strict laws of mathematical calculation? For the existence of the ether is not based only on the phenomena of light: it is an equally necessary postulate to explain those of heat, electricity, and chemical action. We must conceive of our atoms and molecules as forming systems and performing their movements, not in vacuo, but in an all-pervading medium of this ether, to which they impart, and from which they receive, impulses.

These impulses are excessively minute, and when they occur in irregular order they produce no appreciable effect; but when the vibrations of the ether keep time with those of the atoms, the multitude of small effects becomes summed up into one considerable enough to produce great changes. Just so a rhythmic succession of tiny ripples may set a heavy buoy oscillating, and the footfalls of a regiment of soldiers marching over a suspension-bridge may make it swing until it breaks down, while a confused mob could traverse it in safety. The latter affords a good illustration of the way in which molecular structures may be broken down, and their atoms set free to enter into other combinations, by the action of heat, light, or chemical rays beyond the visible end of the spectrum.

Conversely the phenomena of the spectroscope all depend on the fact that the vibrations of atoms and molecules can propagate waves through the ether, as well as absorb ether-waves into their own motions, and thus give spectra distinguished by bright or dark lines peculiar to each substance, by which it can be identified. Whatever ether may be, this much is certain about it: it pervades all space. That it extends to the boundaries of the infinitely great we know from the fact that light reaches us from the remotest stars and nebulæ, and that in this light the spectroscope enables us to detect waves propagated and absorbed by the very same vibrations of the same familiar atoms at these enormous distances as at the earth’s surface. Glowing hydrogen, for instance, is a principal ingredient of the sun’s atmosphere and of those distant suns we call stars, and it affects the ether and is affected by it exactly in the same manner as the hydrogen burning in an ordinary gas-lamp.

In the direction also of the infinitely small, ether permeates the apparently solid structure of crystals, whose molecules perform their limited and rigidly definite movements in an atmosphere of it, as is shown by the fact that in so many cases light and heat penetrate through them. A whole series of remarkable phenomena arise from the manner in which the vibrations of ether which cause light are affected by the structure of the molecules of crystals through which they pass. In certain cases they are what is called polarised, or so affected that while they pass freely if the crystal is held in one direction, they are stopped if it is turned round through an angle of 90° to its former position, so that one and the same crystal may be alternately transparent and non-transparent. It would seem as if its structure were like that of wood, grained, and more easy to penetrate if cut with the grain than against it, so that when a ray of light attempted to penetrate, its vibrations were resolved into two, one with the grain which got through, the other against it which was suppressed; so that the emerging ray, which entered with a circular vibration, got out with only one rectilinear vibration parallel to the diameter which coincided with the grain.

Other crystals of more complicated structure affect transmitted light in a more complex way, developing a double polarity very similar to that induced in the iron filings when brought under the influence of the two poles of the magnet. With this polarised light the most beautiful coloured rings can be produced from the waves of the different colours into which the white light has been analysed in passing through the crystal, which alternately flash out and disappear as the crystal is turned round its axis, and which present a remarkable analogy to the curves into which the iron filings form themselves under the single or double poles of the magnet.

The importance of this will appear afterwards, but for the present it is sufficient to show that the waves of ether which cause light really penetrate through the molecules of crystals, but in doing so may be affected by them.

In dealing with these excessively small magnitudes it may assist the reader who has some acquaintance with mathematics in forming some conception of them, to refer to that refinement of calculation, the differential and integral calculus. And even the non-mathematical reader may find it worth while to give a little attention in order to gain some idea of this celebrated calculus which was the key by which Newton and his successors unlocked the mysteries of the heavens. The first rough idea of it is gained by considering what would happen if, in a calculation involving hundreds of miles, we neglected inches. Suppose we had a block of land to measure, 300 miles long and 200 wide; as there are, say, 5,000 feet in a mile, and the error from omitting inches could not exceed a foot, the utmost error in the measurement of length could not exceed 1/1500000th, and in width 1/1000000th part of the correct amount. In the area of 300 × 200 = 60,000 square miles, the limit of error would, by adding or omitting the rectangle formed by multiplying together these two small errors, not exceed 1/1500000 × 1/1000000 = 1/1500000000000th part. It is evident that the first error is an excessively small part of the true figure, and the second error a still more excessively small part of the first error. But, as we are dealing with abstract numbers, we can just as readily conceive our initial error to be the 1/100th or 1/1000th of an inch, as one inch; and, in fact, diminish it until it becomes an infinitesimally small or evanescent quantity. In doing so, however, it is evident that we shall make the second error such a still more infinitesimally small fraction of the first that it may be considered as altogether disappearing.

The first error is called a differential of the first order and denoted by d, the second a differential of the second order denoted by d₂. Thus if we call the base of our rectangle x and its height y, the area will be xy. Let us suppose x to receive the addition of a very small increment dx, and y the corresponding increment dy, what will be the corresponding increment of the area, or d.xy? Clearly the difference between the old area xy and the new area (x + dx) multiplied by (y + dy). This multiplication gives

The difference between this and xy is xdy + ydx + dx.dy. But dx.dy is, as we have seen, a differential of the second order and may be neglected. Therefore dxy = xdy + ydx. In like manner dx² = (x + dx)²-x² = 2xdx + dx², which last term may be neglected, and dx² = 2xdx. In this way the differentials of all manner of functions and equations of symbols representing dimensions and motions may be found. Conversely the wholes may be considered as made up of an infinite number of these infinitely small parts, and found from them by summing up or integrating the differentials. Thus if we had the equation

xdy + ydx = 2zdz

we know that the left-hand side is the differential of xy, and therefore that by integrating it we shall get xy; while the right side is the differential of z² which we shall get by integrating it. The relation expressed therefore is that xy = z², or, in other words, that a rectangle whose sides are x and y exactly equals a square whose side is z.

The use of this device in assisting calculation will be apparent if we take the case of an area bounded by a curved line. We cannot directly calculate this area, but we can easily tell that of a rectangle. Now it is evident that if we inscribe rectangles in this area ABC, the more rectangles we inscribe the less will be the error in taking their sum as equal to the curved area. This is apparent if we compare fig. 2 with fig. 3. Suppose we take a point P on the curve, call BN = x and PN = y, and suppose Nn to be dx, the differentially small increment of x, and pq = dy the corresponding small increment of y. The area of the rectangle PqnN = PN × Nn = ydx, and differs from the true curvilinear area PpnN by less than the little rectangle of Pq × pq or of dx.dy. But, as we have seen, if we push our division to the first infinitesimal order, or make Nn and pq differentials of x and y, dx.dy may be neglected—i.e. multiply the number of rectangles indefinitely, and the sum of their areas will differ from the true area inclosed by the curve by an error which is evanescent.

If then x and y are connected by some fixed law, as must be the case if the extremity of y traces out some regular curve, the relation between them may be expressed by an equation, which will remain one however often it may be differentiated or again integrated, and whatever modifications or transformations it may receive by mathematical processes which do not alter the essential equality of the two sides connected by the symbol of equality =. Thus by differentiating and casting off as evanescent all differentials of a lower order than that which we are working with, we may arrive at forms of which we know the integrals, and by integrating get back to the results in ordinary numbers, which we were in search of but could not attain directly.

The same thing will apply if our symbols are more numerous, and if they express relations of motion as well as of space, or, in fact, any relations which are governed by fixed laws expressible by equations. If I have succeeded in conveying to the readers any idea of this celebrated calculus, they will perceive what an analogy it presents to the idea of modern physical and chemical science, that of molecules, atoms, and ether, forming differentials of successive orders of the infinitely small. It is certainly most remarkable that while the former was a purely intellectual idea based on mathematical abstractions, and which was invented and worked as an instrument for solving the most intricate astronomical problems for nearly two centuries, without a suspicion that it represented any objective reality: the latter idea, based on actual experiment, seems to show that differentials and integrals have their real counterpart in nature and represent fundamental facts in the constitution of the universe.

Those who are of a mystic or metaphysical turn of mind may discern in this, arguments for matter and laws of matter being after all only manifestations of one universal, all-pervading mind; but in following such speculations we should be deserting the solid earth for cloudland, and passing the limit of positive knowledge into the region where reflections of our own hopes, fears, religious feelings, and poetical sentiments form and dissolve themselves against the background of the great unknown. For the present, therefore, I confine myself to pointing out how these undoubted truths of mathematical science, which have verified themselves in the practical form of enabling us to predict eclipses and construct nautical almanacs, correspond with and throw light upon the equally certain facts of this succession of infinitely small quantities of successive orders in the constitution of matter.

An attempt has recently been made, based on abstruse mathematical calculations, to carry our knowledge of the constitution of matter one step further back, and identify atoms with ether. This is attempted by the vortex theory of Helmholz, Sir W. Thomson, and Professor Tait. It is singular how some of the ultimate facts discovered by the refinements of science correspond with some of the most trivial amusements. Thus the blowing of soap-bubbles gives the best clue to the movement of waves of light, and through them to the dimensions of molecules and atoms; and the collision of billiard-balls, knocked about at random, to the movements of those minute bodies, and the kinetic theory of gases. In the case of the vortex theory the idea is given by the rings of smoke which certain adroit smokers amuse themselves by puffing into the air. These rings float for a considerable time, retaining their circular form, and showing their elasticity by oscillating about it and returning to it if their form is altered, and by rebounding and vibrating energetically, just as two solid elastic bodies would do, if two rings come into collision. If we try to cut them in two, they recede before the knife, or bend round it, returning, when the external force is removed, to their original form without the loss of a single particle, and preserving their own individuality through every change of form and of velocity. This persistence of form they owe to the fact that their particles are revolving in small circles at right angles to the axis or circumference of the larger circle which forms the ring; motion thus giving them stability, very much as in the familiar instance of the bicycle. They burst at last because they are formed and rotate in the air, which is a resisting medium; but mathematical calculation shows that in a perfect fluid free from all friction these vortex rings would be indivisible and indestructible: in other words, they would be atoms.

The vortex theory assumes, therefore, that the universe consists of one uniform primary substance, a fluid which fills all space, and that what we call matter consists of portions of this fluid which have become animated with vortex motion. The innumerable atoms which form molecules, and through molecules all the diversified forms of matter of the material universe, are therefore simply so many vortex rings, each perfectly limited, distinct, and indestructible, both as to its form, mass, and mode of motion. They cannot change or disappear, nor can they be formed spontaneously. Those of the same kind are constituted after the same fashion, and therefore are endowed with the same properties.

The theory is a plausible one, and the reputation of its authors must command for it respectful consideration; but it is as yet a long way from being an established theory which can be accepted as a true representation of facts. In the first place it is based solely on mathematical theory, and not, as in the case of atoms and light-waves, upon actual facts of weight and measurement tested by experiment, and to which mathematical reasoning affords only an aid and supplement. No one has proved the existence of such a medium or of such vortex rings, much less weighed or measured them.

Moreover the theory is open to some very obvious objections. How can aggregations of imponderable matter acquire weight, and become subject to the law of gravity, which, as we have seen, is one of the essential and permanent qualities of atoms? If a cubic millionth of a millimetre of ether formed into a big vortex ring of, say, an atom of mercury, has a weight equal to 200 times that of an atom of hydrogen, which itself has a definite weight, why has it no weight in its original form? And if it had weight, however small, how could the enormous mass of ether filling all space produce no perceptible effect on bodies, even of attenuated cometic vapour, revolving through it with immense velocities? Again, how could these innumerable vortex rings be formed out of the ether without disturbing the uniformity and continuity of the medium, which are essential for the propagation of the light-waves through it? And how could the motions requisite to form the vortex rings be impressed on them de novo consistently with the principle of the conservation of energy? Energy can no more be created out of nothing than matter, by any process known in nature or conceivable by the human intellect; and to assume it is simply a more refined manner of falling back on the supernatural, which is itself only a more refined manner of saying that we know nothing.

For the present, therefore, we must be content with atoms and ether as the ultimate terms of our knowledge of the material or quasi-material components of the universe.

CHAPTER IV.
ENERGY.

Energy of motion and of position—Energy can be transformed, not created or destroyed—Not created by free will—Conservation of mechanical power—Convertibility of heat and work—Nature of heat—The steam-engine—Different forms of energy—Gravity—Molecular energy—Chemical energy—Dynamite—Chemical affinities—Electricity—Produced by friction—By the voltaic battery—Electric currents—Arc light—Induction—Magnetism—The magnetic needle—The electric telegraph—The telephone—Dynamo-electric engine—Accumulator.

Those ultimate elements, however, atoms and ether, only give us what may be called the dead half of the universe, which could not exist without the constant presence of the animating principle of force or energy. Energy is the term generally adopted in the language of science, for force is apt to be associated with human effort and with actual motion produced, while energy is a comprehensive term, embracing whatever produces or is capable of producing motion. Thus, if we bend a cross-bow, the force with which it is bent may either reappear at once in the flight of the arrow, if we let go the string; or it may remain stored up, if we fix the string in the notch, ready to reappear when we pull the trigger. In the former case it is called energy of motion, in the latter energy of position. It is important to realise this distinction clearly, for many of the ordered and harmonious arrangements of the universe depend on the polarity, or conflict with alternate victories and defeats, between those two forms of energy.

Thus if A B is a pendulum suspended at the point A, if we move it from its position of rest A C to A B and hold it there, its whole energy is that of position. If we let it go it swings backwards and forwards between the positions A B and A D, and but for the resistance of the air and the friction at the point of suspension, it would so swing for ever. But in thus swinging what happens? From A B to A C energy of motion keeps gaining on energy of position, until when the pendulum reaches C, it has annihilated it. Energy of position has entirely disappeared, and the whole original force expended in raising the pendulum to A B exactly reappears in the force or momentum of the pendulum at its lowest point. But is this victory final? By no means; energy of position having touched bottom, gathers, like Antæus, fresh vigour for the contest, and from the position A C upwards it gains ground on its adversary until when the pendulum reaches A D it is in its turn completely victorious.

The same alternation between energy of motion and of position takes place in all rhythmical movements such as waves, which, whether in water, air, or ether, are propagated, as in the case of the pendulum, by particles forced out of their position of rest and oscillating between the two energies.

Thus if waves run along an elastic wire A B, the particle P, which has been forced into the position p, oscillates backwards and forwards between p and q, beginning with nothing but energy of position at p, losing it all for energy of motion at P, and regaining it at q. All wave-motions therefore—that is to say, all sound, light, and heat—depend on this primitive polarity.

If we have got this definition of the two forms of energy clearly into our heads, we shall be the better prepared for this further generalisation—the grandest, perhaps, in the whole range of modern science—that energy, like matter, is indestructible, and can only be transformed, but never created or annihilated.

This is at first sight a more difficult proposition to establish in the case of energy than in that of matter. In the latter case we have nothing in our experience that can lead us to suppose that we have ever created something out of nothing; but in the former, our first impression undoubtedly is that we do create force. If I throw a stone at a bird I have an instinctive impression that the force which projects the stone is the creation of my own conscious will; that I had the choice either to throw or not to throw; and that if I had decided not to throw, the impelling force would never have existed. But, if we look more closely at the matter, it is not really so. The chain of events is this: the first impulse proceeds from the visual rays, which, concentrated by the lens of the eye on the retina, give an image of the bird; this sends vibrations along the optic nerve to the brain, setting in motion certain molecules of that organ; these again send vibrations along other nerves to certain muscles of the arm and hand, which contract, and by doing so give out the energy of movement which throws the stone. All this process is strictly mechanical; the eye acts precisely like a camera obscura in forming the image; the nerve-vibrations, though not identical with those of the wires of an electric telegraph, are of the same nature, their velocity can be measured, and their presence detected by the galvanometer; the energy of the muscle is stored there by the slow combustion of the food we have eaten, in the oxygen of the air we have breathed. Take any of these conditions away, and no effort of the will can produce the result. If the nerve is paralysed, or the muscle, from prolonged starvation, has no energy left, the stone will not be thrown, however much we may desire to kill the bird.

Again, precisely the same circle of events takes place in numerous instances without any intervention of this additional factor of conscious will. We breathe mechanically, the muscles of the chest causing it to rise and fall like the waves of the ocean, without any deliberate intention of taking air into the lungs and exhaling it. Nay more, there are instances of what was at first accompanied by the sensation of conscious will, ceasing to be so when the molecular movements had made channels for themselves, as when a piano-player, who had learned his notes with difficulty, ends by playing a complicated piece automatically. The case of animals also raises another difficulty. Suppose a retriever dog sees his master shoot at and miss a hare: shall he obey the promptings of his animal instinct and give chase, or those of his higher moral nature which tell him that it is wrong to do so without the word of command? It is hard to see how this differs from the case of a man resisting or yielding to temptation; and how, if we assign conscious will to the man, we can deny it to the dog.

Reasoning from these premises, some philosophers have come to the conclusion that man and all animals are but mechanical automata, cleverly constructed to work in a certain way fitting in with the equally preordained course of outward phenomena; and that the sensation of will is merely an illusion arising as a last refinement in the adjustment of the machinery. But here comes in that principle of duality or polarity, by which a proposition may be at once true and untrue, and two contradictory opposites exist together. No amount of philosophical reasoning can make us believe that we are altogether machines and not free agents; it runs off us like water from a duck’s back, and leaves us in presence of the intuitive conviction that to a great extent

Man is man and master of his fate.

If this be an illusion, why not everything—evidence of the senses, experiment, natural law, science, as well as morality and religion?

To pursue this farther would lead us far astray into the misty realm of metaphysics, and I refer to it only as showing that the principle of the conservation of energy, standing as it does in apparent contradiction to our natural impressions, requires a fuller demonstration than the kindred principle of the indestructibility of matter.

In the case of ordinary mechanical power it had been long known that the intervention of machinery did not create force, but only transformed it. If a weight of 1 lb., A, just balances a weight of 2 lb., B, by aid of a pulley, and by the addition of a minute fraction, such as a grain, raises it 1 foot, it will be invariably found that A has descended 2 feet. In other words, 1 lb. working through 2 feet does exactly the same work as 2 lbs. working through 1 foot. And whatever may be the intervening machinery the same thing holds good, and the work put in at one end comes out, neither more nor less, at the other, except for a minute loss due to friction and resistance of air. If a force equal to 1 lb. is made, by multiplying the intermediate machinery, to raise a ton a foot from the ground, exactly as much force must have been exerted as if the ton had been divided into 2,240 parts of 1 lb. each, and each part separately lifted.

But although energy cannot be created, at first sight it seems as if it might be destroyed, as when the ton falls to the ground and seems to have lost all its energy, whether of motion or of position. But here science steps in and shows us that it is not destroyed, but simply transformed into another sort of motion, which we call heat.

Some connection between mechanical work and heat had long been known, as in the familiar experiment of rubbing our hands together to warm them; and the practice known to most primitive races of obtaining fire by twirling a stick rapidly in a hole drilled in a block of wood; a practice described by the old Sanskrit word ‘pramantha,’ which means an instrument for obtaining fire by pressure or friction, and which, translated into Greek, has been immortalised by the legend of Prometheus. But it was reserved for recent years, and for an English philosopher, Dr. Joule, to give scientific precision and generality to this idea, by actually measuring the amount of heat produced by a given amount of work, and showing that they were in all cases convertible terms, so much heat for so much work, and so much work for so much heat. He did this by measuring accurately by a thermometer the heat added to a given amount of water by the work done by a set of paddles revolving in it, set in rapid motion by a known weight descending through a known space. The unit of work being taken as that sufficient to raise 1 kilogramme through 1 metre, and that of heat as that required to raise the temperature of one kilogramme of water by 1° Centigrade, the relation between them, as found by a vast number of careful experiments, is that of 424 to 1. That is, one unit of heat is equal to 424 units of work.

In this, and all cases requiring scientific precision, it is better to use the units of the metrical system than our clumsy English standards; but it may be sufficient for the ordinary reader to take the metre, which is about 39·37 inches, as practically a yard, and the kilogramme, which is 15,432 English grains, as practically equal to 2 lbs. This is sufficient to show the much greater energy of the invisible forces which act at minute distances, than that of gravity and other forces which do appreciable mechanical work, the energy of a weight falling from a height of more than 1,300 feet being only sufficient to heat its own weight by 1°.

This proof of the convertibility of work into heat gives much greater precision to our ideas respecting the real nature of heat and its kindred molecular and atomic energies. Heat is clearly not a material substance, for a body does not gain weight by becoming hotter. In the case of all ponderable matter down to the atoms, which are only of the size of cricket-balls compared to that of the earth, any combination which adds matter adds weight, and the weight of the product exactly equals the sum of the weights of the separate factors which have united to form it. Thus, if iron is burnt in oxygen gas, the product, oxide of iron or rust, weighs more than the original iron by just as much as the weight of the oxygen which has been consumed. But heat, light, and electricity add nothing to the weight of a body when they are added to it, and take nothing away when they are subtracted. The inference is unavoidable that heat, like light, is not ponderable matter, but an energy transmitted by waves of the imponderable medium known as ether. This is confirmed by finding that when a ray from the sun is analysed by passing through a refracting prism, one part of the spectrum shows light of various colours, while another gives heat. The hottest part of the spectrum lies in the red and beyond it, showing that the heat-waves are longer, and their oscillations slower, than those of light. Heat-waves also may be made to interfere, and to become polarised, in a manner analogous to the phenomena exhibited by those of light.

There can be no doubt, therefore, that heat, like light, is an energy or mode of motion, transmitted by waves of an imponderable ether, and that it acts on the molecules and atoms of matter by the accumulated successive impulses of those waves on the molecules and atoms which are floating in it, or rather which are revolving in it, in definite groups and fixed orbits, like miniature solar systems or starry universes. We can now see how heat performs work, and why work can be transformed into it.

Heat performs work in two ways. First, it expands bodies—that is, it draws their molecules farther apart against the force of cohesion which binds them together or keeps them moving in definite orbits at definite distances. It is as if it increased the velocity, and therefore the centrifugal force of a system of planets, and so caused them to revolve in wider orbits. The expansion of mercury in a thermometer affords a familiar instance of this effect of heat and the readiest measure of its amount. Secondly, it increases the energy of the molecular motions, so that they dart about, collide, and vibrate with greater force. Thus, as heat increases, evaporation increases, for molecules on the surface are projected with so much force as to get beyond the sphere of the cohesive attraction which binds them to the system, and they dart off like comets into space. Finally, as heat increases, and more and more work is done, against the centripetal force of cohesion, most substances, and doubtless all if we could get heat enough, are converted from solids into fluids, and ultimately into gases, in which latter state the molecules have got altogether beyond the sphere of their mutual attraction, and tend to dart off indefinitely in the direction of their own proper centrifugal motions, unless confined, in which case they dart about, collide, rebound, and exercise pressure on the containing surface.

Conversely, if heat expands bodies, it is given out when they contract. Thus the enormous quantity of heat poured out for millions of years by the sun, is probably owing mainly to the mechanical force of contraction of the original cosmic matter condensing about the solar nucleus.

Again, when gases suddenly expand, their temperature falls, which is the principle by which artificial ice is procured, and frozen beef and mutton are brought from America and Australia, producing, such are the complicated relations of modern society, agricultural depression, fall of rents, and a serious aggravation of the Irish question.

As an example of the converse proposition of the transformation of heat into mechanical work, the steam-engine affords the aptest illustration. The original power came from the sun millions of years ago, and did work by enabling the leaves of plants to overcome the strong mutual affinity of carbon and oxygen in the carbonic dioxide in the air, and store up the carbon in the plant, where it remained since the coal era in the form of energy of position. By lighting the coal, or in other words separating its molecules more widely by heat, we enable them to exert once more their natural affinity for oxygen, and burn, that is recombine into carbonic dioxide. The heat thus produced turns water into steam, which passes through a cylinder, either into a condenser if the steam is at low pressure, or into the outer air if it has been superheated and brought to a higher pressure than that of the atmosphere. The difference of the pressure or elasticity of the steam in the boiler, and of the same steam when it is condensed or liberated, is available for doing work, and, being admitted and released alternately at the two ends of the cylinder, drives a piston up and down, which, by means of cranks and shafts, turns a wheel or does whatever work is required of it. In doing this, heat disappears, being converted into work, and the amount of heat would exactly equal that into which the work would be converted according to Joule’s law, if it could all be utilised without the loss necessarily incurred by friction, radiation, and the still more important absorption of latent heat required to convert water at boiling-point into vapour of the same temperature. This latter is not really an annihilation of the heat, but its conversion into work done in separating the molecules against the force of cohesion. The whole heat, therefore, is transformed into work, mainly molecular work in tearing molecules asunder, and the residue into mechanical work turning spindles and driving locomotives and steamboats.

The intermediate machinery here, including the water in the boiler, is merely the means of applying the original energy in the particular way we desire. The essential thing is the transformation of a certain amount of heat into work by passing, in accordance with the laws of heat, from a hotter to a colder body. The last condition is indispensable, for the nature of heat is to seek an equilibrium by passing from hot to cold, and no work can be got out of it in the reverse way. On the contrary, work must be expended and turned into heat to restore the temperature which has run down. The case is analogous to that of water, which, if raised by evaporation or stored up in reservoirs at a level above the sea, can be made to turn a wheel while it is running down; but when it has all run down to the sea level, can do no more work, and can only be pumped up again to a higher level by the expenditure of fresh work. Owing to this tendency of heat we can see that, although matter and energy are to all appearance indestructible, the present constitution of the universe is not eternal. The animating energy of heat is always tending to obliterate differences of temperature, and bring all energy down to one uniform dead level of a common average, in which no further life, work, or motion are possible. Fortunately this consummation is far off, and for many tens or hundreds of millions of years the inhabitants of this tiny planet may feel fairly secure, and need not, like the late Dr. Cumming, of millenarian celebrity, introduce breaks in the leases of their houses to provide against the contingency of the world coming to an end at an early date.

Dismissing, then, to the remote future any speculations as to the failure of this essential element of active energy, let us rather consider the various protean forms in which it shows itself.

1. The energy of visible motion, which, as we have seen, may be transformed into an equivalent amount of energy of position.

2. Molecular energy, which causes the cohesive attraction, repulsion, and other proper motions of these minute and invisible particles of matter.

3. Energy of heat and light, which are transmitted by waves of the assumed imponderable medium called ether.

4. Energy of chemical action, by which the small ultimate particles of ponderable matter, called atoms, separate and combine into the various combinations of molecules constituting visible matter, in obedience to certain affinities, or inherent attractions and repulsions.

5. Electrical energy, which includes magnetism as a special instance.

All these forms of energy may exist, as in the case of visible energy, either as energies of motion or of position, and the actual constitution of the universe is due in a great measure to the alternation of these two energies. Thus all wave-motion, whether it be of the waves of the sea grinding down a rocky coast, of the air transmitting sound, or of ether transmitting light and heat, are instances of energies of motion and of position, conflicting with one another and alternately gaining the victory. So also a pound of gunpowder or dynamite has an immense energy of position, which, when its atoms are let loose from their mutual unstable connection by heat or percussion, manifests itself in an enormous energy of motion, which is more or less destructive according to the rapidity with which the atoms rush into new combinations.

Let us consider these different energies a little more in detail. The energy of visible motion is manifested principally by the law of gravity, under which all matter attracts other matter directly as the mass and inversely as the square of the distance. It is a universal and uniform law of matter, and can be traced without change or variation from the minutest atom up to the remotest double star. The energy of living force might, at first sight, be considered as another of the commonest causes of visible motion; but, when closely analysed, it will be found that what appears as such is only the result of molecular energy of position stored up in the living body by chemical changes during the slow combustion of food, and that nothing has been added by any hypothetical vital force. The conscious will seems to act in those cases simply as the signalman who shows a white flag may act on a train which has been standing on the line waiting for it. The energy which moves the train is due entirely to the difference of heat, which has been developed by the combustion of coal, between the steam in the boiler and the steam when allowed to escape into the air; and this energy came originally from the sun, whose rays enabled the leaves of growing plants to decompose carbonic dioxide and store up the carbon in the coal. Of this force of gravity causing visible motion we may say that it is comparatively a very weak force, which acts uniformly over all distances great or small.

Molecular energies, on the other hand, act with vastly greater force, but at very small distances, and appear sometimes as attractive and sometimes as repulsive forces. Thus solid bodies are held together by a force of cohesion which is very powerful, but acts only at very small distances, as we may see if we break a piece of glass and try to mend it by pressing the broken edges together. We cannot bring them near enough to bring the molecular attraction again into play and make the broken glass solid. But the same glass acts with repellent energy if another solid tries to penetrate it, so that we can walk on a glass floor without sinking into it. Heat also, by increasing the distance between the molecules, first weakens the cohesive force so that the solid becomes fluid, and finally overcomes it altogether, so that it passes into the state of gas in which the centripetal attraction of the molecules is extinguished, and they tend to recede further and further from each other under the centrifugal force of their own proper velocities. The great energy of molecular forces will be apparent from the fact that a bar of iron, in cooling 10° Centigrade, contracts with a force equal to a ton for each square inch of section, as exemplified in the tubular bridge across the Menai Straits, where space has to be allowed for the free contraction and expansion of the iron under changes of temperature.

Chemical energy, or the mutual attractions and repulsions of atoms, is even more powerful than that of molecules. It displays itself in their elective affinities, or what may be called the likes and dislikes, or loves and hatreds, of these ultimate particles. Perhaps the best illustration will be afforded by that ‘latest resource of civilisation,’ dynamite. This substance, or to give it its scientific name, nitro-glycerine, is composed of molecules each of which is a complex combination of nine atoms of oxygen, five of hydrogen, three of nitrogen, and three of carbon. Of these, oxygen and hydrogen have a strong affinity for one another, as is seen by their rushing together whenever they get the chance, and by their union forming the very stable compound, water. Oxygen and carbon have also a very strong affinity, and readily form the stable product carbonic dioxide gas. Nitrogen, on the other hand, is a very inert substance; its molecule consists of two atoms of itself which are bound together by a strong affinity, and can only be coaxed with difficulty into combinations with other elements, forming compounds which are, as it were, artificial structures, and very unstable. We see this in the air, which consists mainly of oxygen and nitrogen, but not in chemical combination, the oxygen being simply diluted by the nitrogen, as whisky is with water, with the same object of diluting the too powerful oxygen or too potent alcohol, and enabling the air-breather or whisky-drinker to take them into the system without burning up the tissues too rapidly. If nitrogen had more affinity for oxygen it would combine chemically with it, and we should live in an atmosphere of nitrous oxide, or laughing gas.

The molecule, therefore, of nitro-glycerine resembles a house of cards, so nicely balanced that it will just stand, but will fall to pieces at the slightest touch. When this is supplied by a slight percussion the molecule falls to pieces and is resolved into its constituent atoms, which rush together in accordance with their natural affinities, forming an immense volume of gas, partly of water in the form of steam where oxygen has combined with hydrogen, and partly of carbonic dioxide where it has combined with carbon, leaving the nitrogen atoms to pair off, and revert to their original form of two-atom molecules of nitrogen gas. It is as if ill-assorted couples, who had been united by matrimonial bonds tied by the manœuvres of Belgravian mothers, found themselves suddenly freed by a decree of divorce a vinculo matrimonii, and rushed impetuously into each other’s arms, according to the laws of their respective affinities. So striking is the similitude that one of Goethe’s best-known novels, the ‘Wahlverwandschaften,’ takes its title from the human play of these chemical reactions. The enormous energy developed when these atomic forces are let loose and a vast volume of gas almost instantaneously created, is attested by the destructive force by which the hardest rocks are shattered to pieces and the strongest buildings overthrown.

These loves and hatreds, or, as they are termed, chemical affinities and repulsions of the atoms, are the principal means by which the material structure of the universe is built up from the original elements. The earth, or solid crust of the planet we inhabit, consists mainly of oxidised bases, and is due to the affinity of oxygen for silicon, calcium, aluminium, iron, and other primary elements of what are called metals. This affinity enables them to make stable compounds, which, under the existing conditions of temperature and otherwise, hold together and are not readily decomposed. Water in like manner, in all its forms of waves, seas, lakes, rivers, clouds, and invisible vapour, is due to the affinity between oxygen and hydrogen forming a stable compound. Salt again is owing to the affinity of chlorine for sodium, and so for nearly all the various products with which we are familiar, oxygen and nitrogen in the air we breathe being almost the only elements which exist in their primary and uncombined state in any considerable quantities, and form an essential part of the conditions which render our planet a habitable abode for man and other forms of life.

We shall see presently something more of the nature of these affinities, and the laws by which they act; but before entering on this branch of the subject we must consider the remaining form in which the one indestructible energy of the universe manifests itself, viz. that of electricity.

Electricity is the most subtle and the least understood of these forms. In its simplest form it appears as the result of friction between dissimilar substances. Thus if we rub a glass rod with a piece of silk, taking care that both are warm and dry, we find that the glass has acquired the property of attracting light bodies, such as little bits of paper, or balls of elder-pith. Other substances, such as sealing-wax and amber, have the same property. Pursuing our research further we find that this influence is not, like that of gravity, uniform and always acting in the same direction, but of two kinds, equal and opposite. If we touch the pith-ball by the excited glass rod, it will after contact be repelled; but if we bring the ball which has been excited by contact with the glass within the influence of a stick of sealing-wax which has been excited by rubbing it with warm dry flannel, the ball instead of being repelled is attracted.

Conversely, if the pith-ball has been first touched by excited sealing-wax, it will afterwards be repelled by excited sealing-wax and attracted by excited glass. It is clear, therefore, that there are two opposite electricities, and that bodies charged with similar electricities repel, and with unlike electricities attract, one another. For convenience, one of these electricities, that developed in glass, is called positive, and the other negative; and it has been clearly proved that one cannot exist without the other, and that whenever one electricity is produced, just as much is produced of an opposite description. If positive electricity is produced in glass by rubbing it with silk, just as much negative electricity is produced upon the silk.

Another primary fact is that some substances are able to carry away and diffuse or neutralise this peculiar influence called electricity, while others are unable to do so and retain it. The former are called conductors, the latter non-conductors. Thus, glass is an insulator or non-conductor, while metal is a conductor of electricity; and the reason why the substances rubbed together, as glass and silk, must be dry is that water, in all its forms, is a conductor which carries away the electricity as fast as it is produced.

These facts have given rise to a theory—which is after all not so much an explanation as a convenient mode of expressing the facts—of the existence of two opposite electric fluids, which, in the ordinary or unexcited body, are combined and neutralise one another, but are separated by friction, and flow in opposite directions, accumulating at opposite poles, or, it may be, one being accumulated at one pole, while the other is diffused through some conducting medium and lost sight of. The active electricity, be it positive or negative, thus accumulated at one pole, and retained there by the substance in contact with it being a non-conductor, disturbs by its influence the electrical equilibrium of any body brought near to it, separates its two fluids, and attracts the one opposite to itself. This attraction draws the light body towards it until contact ensues, when the electric fluid of the excited body flows into the smaller one, so that its opposite electricity is expelled, and it is in the same condition as its exciter, and therefore liable to be repelled by a similar exciter, or attracted by an opposite one which formerly repelled it.

It is evident, without going further, that there is a great analogy between electrical energy and those of heat and of chemical affinity. The same mechanical work—viz. friction—which generates heat, generates electricity. The chief difference seems to be that friction may be transformed into heat when the same substances are rubbed together, as in the case of obtaining fire by the friction of wood; but electricity can only be obtained by friction between dissimilar substances. Thus no electricity is obtained by rubbing glass upon glass, or silk upon silk, or upon glass covered with silk, though a slight difference of texture is sometimes sufficient to separate the electric fluids. Thus if two pieces of the same silk ribbon are rubbed together, lengthways, no electricity is produced, but if crossways, one is positively, and the other negatively, electrified. In this respect the analogy is evident to chemical affinity, which, in like manner, only acts between dissimilar bodies.

In order, however, to carry the proof of the identity of these forms of energy beyond the sphere of vague analogy, we must follow up electricity far beyond the simple manifestations of the glass rod and sealing-wax, and pursue it to its origin, in the transformations of chemical action and mechanical work, in the voltaic battery, the electric telegraph, the telephone, and the dynamo.

The voltaic battery, in its simplest form, is a trough containing an acid liquid in which pairs of plates of different metals are immersed. It is evident that if the action of the acid on each metal were precisely the same, equal quantities of each would be dissolved in the acid, and the equilibrium of chemical energies would not be affected. But, the action being different, this equilibrium is disturbed, and if the sum of these disturbances for a number of separate pairs of plates can be accumulated, it will become considerable. This is done by connecting the plates of the same metal in each cell by a metallic wire covered by some non-conducting substance. There are, therefore, two wires, one to the right hand, the other to the left, the loose extremities of which are called the poles of the battery. If we test these poles as we did the glass rod and stick of sealing-wax, we find that one pole is charged with positive and the other with negative electricity. In other words, the chemical energy, whose equilibrium was disturbed by the unequal action of the acid on the plates of different metals, has been transformed into electrical energy manifesting itself, as it always does, under the condition of two equal and opposite polarities. If we connect these two poles with one another the two electricities rush together and unite, and there is established what is called an electrical current circulating round the battery. As the chemical action of the acid on the metals is not momentary but continuous, the acid taking up molecule after molecule of the metal, so also the current is continuous. When we call it a current, the term is used for the sake of convenience, for as the current, as we shall presently see, will flow along the wire or other conducting substance for immense distances, as across the Atlantic, with a velocity of many thousands of miles per second, we can, no more than in the case of light, figure it to ourselves as an actual transfer of material particles swept along as by a river running with this enormous velocity, but necessarily as a transmission of some form of motion travelling by waves or tremors through the all-pervading ether in which the atoms of the conducting wire are floating. Be this as it may, the effect of these electric currents is very varied and very energetic. It can produce intense heat, for if, instead of uniting the two poles, we connect them by a thin platinum wire, it will, in a few seconds, become heated to redness. If the connecting wire is thicker, heat will equally be generated but less intense, thus maintaining the analogy to the current which rushes with more impetuosity through a narrow than through a wide channel. If the poles are tipped with a solid substance like carbon, whose particles remain solid under great heat, when they are brought nearly together intense light is produced and the carbon slowly burns away. This produces what is called the arc light, which gives such a strong illuminating power and is coming into general use for lighting up large spaces.

Another transformation is back again into chemical energy, which is shown by the power of the electric current to decompose compound substances. If, for instance, the poles of a battery are plunged into a vessel containing water, the molecules of the water will be decomposed and bubbles of oxygen gas will rise from the positive, and of hydrogen from the negative, pole.

Another effect of electrical currents is that of attraction and repulsion on one another. If two parallel wires, free to move, carry currents flowing in the same direction as from positive to negative, or vice versâ, they will attract one another; if in opposite directions, they will repel. Electrical currents also work by way of induction, that is, they disturb the electrical equilibrium of bodies brought within their influence and induce currents in them. Thus, if we have two circular coils of insulated wire placed near each other, one on the right hand, the other on the left, and connect the extremities of the right-hand coil with the poles of a battery, when the connection is first made and the current begins to flow, a momentary current in the opposite direction will pass through the left-hand coil. This will cease, and as long as the current continues to flow through the right-hand coil there will be no current through the other; but if we break the contact between the right-hand coil and the battery, there will be again a momentary current through the left-hand coil, but this time in the same direction as the other. The same effect will be produced if, instead of making and breaking contact in the right-hand coil, we keep the current constantly flowing through it, and make the right-hand coil alternately approach and recede from the other coil. In this case, when the right-hand coil approaches, it induces an opposite current in the left-hand one; and when it recedes, one in the same direction as that of the primary.

These phenomena of induction prepare us to understand the nature of magnets, and the magnetic effects produced by electrical currents. If an insulated wire is wrapped round a cylinder of soft or unmagnetic iron, and a current passed through the wire, the cylinder is converted into a magnet and becomes able to sustain weights. If the current ceases, the cylinder is no longer a magnet, and drops the weight. A magnet is therefore evidently a substance in which electric currents are circulating at right angles to its axis, and a permanent magnet is one in which such currents permanently circulate from the constitution of the body without being supplied from without. The earth is such a magnet, and also iron and other substances, under certain conditions.

This being established, it is easy to see why an electrical current deflects the magnetic needle. If such a needle is suspended freely near a wire parallel with it, on a current being passed through the wire it must attract if similar, or repel if dissimilar, the currents which are circulating at right angles to the axis of the needle, and thus tend to make the needle swing into a position at right angles with the wire so that its currents may be parallel to that of the needle. This is the reason why the needle in its ordinary condition points to the north and south, or rather to the magnetic poles of the earth, because its currents are influenced by the earth currents which circulate parallel to the magnetic equator. The deviation of the needle from this direction, caused by any other current, like that passed along the wire, will depend on the strength of the current, which may be measured by the amount of deflection of the needle. The direction in which the needle deflects, viz. whether the north pole swings to the right or to the left, will depend on the direction of the current through the wire. The direction of the circular currents which form a magnet is such that if you look towards the north pole of a freely suspended cylindrical magnet—i.e. if you stand on the north of it and look southwards—the positive current will ascend on your right hand, or on the west side, and descend on the east. It follows that unlike poles must necessarily attract, and like poles repel one another, for in the former case the circular currents which face each other are going in the same, and in the latter in opposite directions.

The reader is now in a position to understand the principle of the electric telegraph, that wonderful invention which has revolutionised human intercourse and, to a great extent, annihilated space and time. It originated in the discovery made by Oersted, a Danish savant, that the effect of an electric current was to make a magnet swing round, in the endeavour to place itself at right angles to it. The conducting power of insulated copper wire is such that it practically makes no difference whether one of the wires connected with the pole of a battery is two feet or 2,000 miles in length, and the earth, being a conducting medium, supplies an equal extension from the other pole, so that a closed electric circuit may be established across the Atlantic as easily as within the walls of a laboratory.

If, therefore, a magnetic needle is suspended at the American end, it will respond to every electrical current, and to any interruption, renewal, or reversal of that current established in England. The needle may thus be made to swing to the right or left, by forming or reversing a current through the wire; and it will return to its position whenever the current is interrupted, and repeat its movement whenever the current is renewed. In fact it may be made to move like the arm of the old-fashioned telegraph, or of a railway signal. It only remains to have a machine by which the operator can form and interrupt currents rapidly, and a code by which certain movements of the needle stand for certain letters of the alphabet, and you have the electric telegraph.

There are many ingenious applications of the machinery, but in principle they all resolve themselves into transformations of energy. Chemical energy is transformed into electric energy, and that again into mechanical work in moving the needle.

The telephone is another instance of similar transformations. Here spoken words create vibrations of the air, which cause corresponding vibrations in a thin plate or disc of metal at one end, which are conveyed by intermediate machinery to a similar disc at the other end, whose vibrations cause similar vibrations in the air, reproducing the spoken words at a distance which may be a great many miles from the speaker.

The great inventions of modern science which have so revolutionised society are all instances of the laws of the conservation of energy. Man makes the powers of nature available for his purposes by transforming them backwards and forwards, now into one, now into another form of energy, as required for the result he wishes to attain. He wants mechanical power to pump water or drive a locomotive or steamboat: he gets it from the steam-engine, by transforming the energy of heat in coal, which came ages ago from the energy of chemical action produced by the sun’s rays in the green leaves of growing plants. He wants to send messages in a few seconds across the Atlantic: he does it by transforming chemical energy into electricity in a voltaic battery, sending its vibrations along a conducting wire, and converting it at the far end into mechanical power, making a magnetic needle turn on its axis and give signals. If, instead of sending a message, he wants to hold a conversation at a distance, he invents the telephone, by which sound-vibrations of air are transformed into vibrations of a disc, then into electric currents, then into vibrations of a distant disc, and finally back again to spoken words. Or, if he wants light, he turns electricity into it by tipping the poles of his battery with carbon and bringing them close together.

The latest inventions of electrical science—the dynamo and the accumulator—afford remarkable instances of this convertibility of one primitive energy into different forms. In the instance just quoted of obtaining light from electricity by the voltaic battery, the cost has hitherto proved an obstacle to its adoption. The electrical energy is all obtained from the transformation of the heat produced in the cells by the chemical action on the metal used, which is commonly zinc. Now, the heat of combination of zinc with oxygen is only about one-sixth of that of coal, while the cost of zinc is about twenty times as great. Theoretically, therefore, energy got by burning zinc costs 120 times as much as that got by burning coal. Practically the difference is not nearly so great, for there is very little loss of energy in the battery by the process of conversion, while the best steam-engine cannot convert into work as much as twenty per cent, of the heat energy in the coal consumed. Still, after making every allowance, the cost of energy from zinc remains some twenty times as great as from coal, so that unless some process is found for obtaining back the zinc as a residual product, there is no prospect of this form of electricity being generally available for light or for mechanical power.

The dynamo is an instrument invented for the mechanical generation of electricity by taking advantage of the principle that electrical energy is produced by moving magnets near coils of wire, or coils of wire near magnets. A current is thus started by induction, and, once started, the mechanical power exerted in making the magnet or coils revolve is continually converted into electricity until the accumulated electrical energy becomes very powerful. The original energy comes of course from the coal burned in the steam-engine which makes the magnet or coils revolve.

The principle of the conservation of energy is well illustrated by the fact that as the dynamo generates an electric current if made to revolve, conversely it may be made to revolve itself if an electric current is sent through it from an exterior source. It is, therefore, available not only as a source of light in the former case, but as a direct source of mechanical power in the latter. It is on this principle that electric engines are constructed and electric railways are worked. Here also it is a question of cost and convenience, for you can only get electricity enough either to light a street or to drive an engine, by an original steam-engine or other motive power to work the dynamo, and a system of conducting wires to convey the electricity to the place where the light or power is wanted. Where the motive power is supplied by nature, as in the case of tidal or river currents or waterfalls, it is quite possible that power may be obtained in this way to compete with that obtained directly from the steam-engine; but there are as yet considerable practical difficulties to be overcome in the transmission of any large amount of energy for long distances.

To overcome some of these difficulties the accumulator has been invented, which affords yet another remarkable instance of the transformation of energy. It consists of two lead plates immersed in acidulated water. When a strong electrical current is sent through the water, it decomposes it, the oxygen going to one lead plate and the hydrogen to the other. The oxygen attacks the lead plate to which it goes, forming peroxide of lead; while the hydrogen reduces any oxide in the other plate, producing pure lead, and leaving a film of surplus hydrogen on the surface. The charging current is then reversed, so that the latter plate is now attacked and the former one reduced, when the current is again reversed. By continuing this process the surfaces of both lead plates become porous, so that they present a large surface, and can therefore hold a great deal of peroxide of lead. The charging current being now broken, the oxygen which has been forcibly separated from the liquid seeks to recombine with hydrogen; and if the two lead plates are joined by a wire, this effort of the oxygen generates an electrical current in the opposite direction to the original one, which is the current utilised. Electricity is thus stored up in a portable box, where it can be kept till wanted, when it is drawn out by connecting the plates, and as a large amount of energy has been accumulated the current which is produced lasts for a considerable time.

Unfortunately accumulators are bulky, heavy, and expensive, and nearly half the energy of the original charging current is lost in obtaining the reversed or working current. They are therefore not as yet adapted for general use, though perfectly capable of supplying either light or motive power, for both which purposes they have been successfully applied in special cases. The future both of electric power and electric lighting is now reduced entirely to a question of cost; and though it is hard to beat gas and the steam-engine, with cheap coal, and air and water for nothing, it is possible that by using natural sources of power to move dynamos, and by obtaining zinc back as a residual product in batteries, electricity may in certain cases carry the day.

CHAPTER V.
POLARITY IN MATTER.

Ultimate elements of universe—Built up by polarity—Experiment with magnet—Chemical affinity—Atomic poles—Alkalies and acids—Quantivalence—Atomicity—Isomerism—Chemical stability—Thermochemistry—Definition of atoms—All matter built up by polar forces.

I almost fear that by this time some of my readers may think that I have seduced them under false pretences to read long chapters of dry science, when they had been led from the introduction to anticipate discussions on the more immediately interesting topics of morals, religions, and philosophies. My excuse must be that these scientific subjects are really of extreme interest in themselves and indispensable as a solid basis for the superstructure to be raised on them. How can I attempt to show that the law of polarity extends to the more complex problems of human thought and life, if I fail in establishing its application to the simpler case of inorganic force and matter? It must be recollected also that among the primitive polarities is that of author and reader. It is my part to endeavour to present the leading facts and laws of the material universe in such plain and popular language that the ordinary reader who has neither time nor faculty for special studies may apprehend them clearly without excessive effort, or extraordinary intelligence. But it is the reader’s part to supply a fair average amount of attention, and above all to feel an interest in interesting matters. Cleverness and curiosity are very much convertible terms, and the clearest exposition is thrown away on the torpid mind which views the marvellous universe in which he has the privilege to live, with the stupid apathy of the savage, taking things as they come without caring to know anything about them.

For the reader’s part of the work I am not responsible; but for my own I am, and I proceed therefore to give in my own way, and with the best faculty that is in me, a clear summary of such of the fundamental facts and laws of nature as seem necessary for the work I have undertaken.

From the preceding chapters we are now able to realise what are the ultimate elements of the material universe, and it remains to show how they are put together. The elements are ether, energy, and matter.

First, ether: a universal, all-pervading medium, imponderable or infinitely light, and almost infinitely elastic, in which all matter, from suns and planets down to molecules and atoms, float as in a boundless ocean, and whose tremors or vibrations, propagated as waves, transport the different forms of energy, light, heat, and electricity, across space.

Secondly, energy: a primitive, indestructible something, which causes motion and manifests itself under its many diversified forms, such as gravity, mechanical work, molecular and atomic forces, light, heat, electricity, and magnetism, all of which are merely Protean transformations of the one fundamental energy, and convertible into each other.

Thirdly, matter: the ultimate elements of this are atoms, which combined form molecules, or little pieces of ordinary matter with all its qualities, which are the bricks used in building all the varied structures of the organic and inorganic worlds. Of these atoms some seventy have never yet been divided, and therefore, although we may suspect that they are merely combinations or transformations of one original matter, we must be content for the present to consider them as elementary. In like manner we may suspect that matter is in reality only another form of energy, and that the impression of solidity is given by the action of a repellent force which is very energetic at short distances. If this were established we might look forward to the generalisation that energy was the one reality of nature; but for the present it is a mere speculation, and we must be content with over seventy elementary atoms as ultimate facts. In any case this much is certain, that matter, like energy, is indestructible. We have absolutely no experience of either of them being created or annihilated. Nay, more, we have no faculties to enable us even to conceive how something can be made out of nothing, and all we know, or can ever know, about these primitive constituents of the universe is of their laws of existence, their evolutions and their transformations.

Minute as the atoms and molecules are, we must conceive of them not as stationary and indissolubly connected, but rather as little solar systems in which revolving atoms form the molecule, and revolving molecules form the matter, held together as separate systems by their proper energies and motions, until some superior force intruding breaks up the system and sets its components free to form new combinations.

What is the principle which thus forms, un-forms, and re-forms the various combinations of atomic and molecular systems by which the world is built up from its constituent elements? It is polarity.

As I began with the illustration of the magnet introducing order and harmony into the confused mass of iron filings, let me take this other illustration from the same source. If we place an iron bar in contact with the pole of a magnet, the bar becomes itself a magnet with opposite poles to the original one, so that as opposite poles attract, the iron bar adheres to it. Bring a lump of nickel in contact with the further end or free pole of the iron bar, and the nickel also will be magnetised and adhere. Let the lump of nickel be as large as the pole of the iron bar is able to support, and now bring a lump of soft iron near this pole. It will drop the nickel and take the iron. This is exactly similar to those cases of chemical affinity in which a molecule drops one of its factors and takes on another to which its attraction is stronger. If iron rusts in water it is because the oxygen atom drops hydrogen to take iron just as the magnet dropped nickel.

The polarity of chemical elements is attested by the fact that when compounds are decomposed by the electric current, the different elementary substances appear at different poles of the battery. Thus, oxygen, chlorine, and non-metallic substances appear at the positive pole; while hydrogen, potassium, and metals generally, appear at the negative one. The inference is irresistible that the atoms had in each case an opposite polarity to that of the poles to which they were attracted. This is confirmed by the fact that the radicals, i.e. the elementary atoms or groups of atoms which have opposite polarities, combine readily; while those which have the same polarity, as two metals, have but slight affinity for each other. Like therefore attracts unlike, as in all cases of polarity, and the greater the degree of unlikeness the stronger is the attraction. Thus, the radicals of all alkalies are electro-positive, and appear at the negative pole of a battery; while those of acids are all electro-negative, and the higher each stands in its respective scale of polarity the more strongly does it show the peculiar qualities of acid or alkali and the more eagerly does it combine with its opposite.

Acids and alkalies are, in fact, all members of the same class of compounds called hydrates, because a single atom of hydrogen is a common feature in their composition. This atom is coupled with a single atom of oxygen, which may be conceived of as the central magnet holding the hydrogen atom at one pole, while at the other it holds either a single atom of some metallic element, such as potassium or sodium, or a group consisting of such an element together with atoms of oxygen, so constituted as to present a single pole to the attraction of the central oxygen atom. Thus, if K stands for kali or potassium, N for nitrogen, O for oxygen, and H for hydrogen, we may have the compounds

H—O—K

and

The former is the molecule of potassic hydrate, which is the most caustic or strongest of alkalies; the latter, that of nitric acid, the most corrosive or powerful of acids. These are the extremes of the series, of which there are many intermediate members, all being more or less alkaline, that is caustic and turning litmus-paper blue, when the third element is a simple metallic atom; and acid, corrosive, and turning litmus-paper red, when it is a compound radical of a group of metallic and oxygen atoms. This shows to what an extent whole classes of substances may have a general resemblance in their constitution, and yet differ most widely in their qualities by the substitution of one element for another.

These special qualities may be made to diminish and finally disappear by mixing the two opposite substances, or, as it is called, neutralising an acid by an alkali or an alkali by an acid. Thus, if hydrochloric acid, HCl, be poured into a solution of sodic-hydrate, Na—O—H, the alkaline qualities of the latter diminish and finally disappear, the result of the neutral solution being water, H—O—H, and sodic-chloride, or common salt, Na—Cl. It is evident that this result has been produced by the hydrogen atom in H—Cl and the sodium atom in Na—O—H changing places, the former preferring to unite with oxygen to form water, while the displaced sodium atom finds a refuge with chlorine. The oxygen atom has dropped sodium and taken hydrogen, just as the magnet dropped nickel and took iron.

This polarity of chemical elements manifests itself in different ways. In some cases it appears like that of a magnet, in which there are two opposite poles, and two only, one at each end. Thus oxygen (O) is bipolar, and its atom holds together two atoms of hydrogen (H) in forming the molecule of water, which may be represented as H+-O+-H, which is equivalent to

. Others again, like hydrogen and chlorine, seem to have only a single pole, as in the case of electricity in an excited glass rod, and have to create for themselves the opposite pole, which is the indispensable condition of all polarity, by induction in another body. Thus, muriatic or hydrochloric acid is formed by the union of a single atom of chlorine, which is strongly negative, with a single atom of hydrogen, in which it appears to have induced a positive pole: though the combination is not a very stable one, for if an element with a stronger positive pole of its own is presented to the chlorine, it drops the hydrogen, just as the magnet drops the nickel. Other atoms are multipolar, and seem as if made up of more than one magnet, or rather as if the atom had regular shape like a triangle, square, or pentagon, and each angle was a pole, thus enabling it to unite with three, four, five, or more atoms of other substances. Thus, one atom of nitrogen unites with three of hydrogen, one of carbon with four of hydrogen, and so on. Every substance has, therefore, what is called its ‘quantivalence,’ or power of uniting with it a greater or less quantity of other atoms, and conversely that of replacing in combinations other atoms, or groups of atoms, the sum of whose quantivalence equals its own. Thus, one atom of carbon, which has four poles, combines with four atoms of hydrogen or chlorine, which is unipolar, but with only two of oxygen, which are bipolar; while the oxygen atom combines with two of hydrogen, and that of chlorine with one atom only of hydrogen. The analogy between the single atomic and electrical poles on the one hand, and the dual and magnetic poles on the other, will be evident if we consider what occurs if a pith-ball, electrified positively, is brought near a similar ball electrified negatively. They attract each other, and the one becomes the pole of the other; but if separated, each carries with it its own electrical charge. But the separate balls or poles, though no longer influencing each other, are not isolated, for each draws by induction an electrical charge opposite to its own to the extremity of the nearest conductor, and thus creates for itself a new or second pole. Polarity, in fact, involves opposition of relations, or two poles, and electrical only differs from magnetic polarity in the fact that in the latter the two poles are in the same body, while in the former they are in separate bodies.

For pith-balls read atoms, and we have an explanation of the univalent atoms like those of chlorine and sodium which act as single poles; and this is confirmed by the fact that such atoms are never found isolated, but are always associated in a molecule with at least one other atom which forms the opposite pole of the molecular system. Bivalent or magnetic atoms, on the other hand, which have two poles, like those of mercury and zinc, may constitute a complete polar system and be found isolated, and form the class of molecules which consist of single atoms.

This conception of the polarity of atoms enables us to understand the way in which the almost infinite variety of substances existing in the world is built up from a comparatively few simple elements. Atoms and radicals, which are multipolar, can attract and form molecules with as many other atoms or radicals as they have poles. This is called their degree of atomicity, which is the same as their quantivalence; and each of these atoms or radicals may be replaced by some other atom or radical, which presents to any pole a more powerful polarity. Thus, compounds may be built up of great and varied complexity, for the quality of any compound may be greatly altered by any one of the substitutions at any one of the poles. And the molecules, or small specimens of matter, may be thus built up into very complex aggregations of atoms, some single molecules containing more than a hundred atoms. Thus, carbon has four poles, or is quadrivalent, and its atoms possess the power of combining among themselves to an almost indefinite extent and forming groups of great stability. Thus, carbon radicals may be formed in very great number, each affording a nucleus upon which compound radicals may be built up, so that carbon has been aptly called the skeleton of almost all the varied compounds of the more complex forms of inorganic matter as well as the principal foundation of organic life.

Nor is this all, for the qualities of substances depend not only on the qualities of their constituent elements, but also on the manner in which these elements are grouped. Two substances may have exactly the same chemical composition and yet be very different. We may suppose that the same elements affect us differently according as they are grouped. Thus, the same bricks may be built up either into a cube or pyramid, which forms are extremely stable and can only be taken in pieces brick by brick; or into a Gothic arch, which all tumbles to pieces if a single brick forming the keystone is displaced. As an instance of this, butyric acid, which gives the offensive odour to rancid butter, has exactly the same composition as acetic ether, which gives the flavour to a ripe apple. They consist of the same number of atoms of the same elements—carbon, hydrogen, and oxygen—united in the same proportions. This applies to a number of substances, and is called Isomerism, or formation of different wholes from the same parts.

The principle of polarity, therefore, aided by the subsidiary conditions of quantivalence, atomicity, and isomerism, gives the clue to the construction of the inorganic world out of some seventy elementary substances. Of the substances thus formed, whether of molecules or of combinations of molecules, some are stable and some unstable. As a rule the simpler combinations are the most stable, and instability increases with complexity. Thus the diamond, which is merely a crystal of pure carbon, is very hard and indestructible; while dynamite, or nitro-glycerine, which is a very complex compound, explodes at a touch.

The stability of a substance depends partly on the stable structure of its component elements, and partly on their mutual affinity being strong enough to keep them together in presence of the attractions of other outside elements, which, in the case of most natural substances at the surface of the earth, consist principally of air and water. Thus, the rocks, earths, metallic oxides, water, carbonic dioxide, and nitrogen are extremely stable, and resist decomposition, or chemical union with other substances, with great energy. With regard to all substances this law holds good, that the tendency is to fall back from a less stable to a more stable condition, and that such a falling back is always attended with an evolution of heat; while, on the other hand, heat is always absorbed and disappears whenever the elements of a more stable substance are made to enter into a less stable condition. Thus, when wood burns, there is a falling back from a substance unstable, on account of its affinity for the oxygen in the air, into the stable products, carbonic dioxide and water, and the heat evolved is the effect of this fall.

As the tendency of all changes is towards stability we arrive at the following law, which is one of the most recent generalisations of modern chemistry: In all cases of chemical change the tendency is to those products whose formation will determine the greatest evolution of heat.

This, however, does not imply that the tendency may not be overcome and unstable products formed, for just as a weight may be lifted against the force of gravity, so may the chemical tendency be overcome by a sufficient energy acting against it. Heat is the principal means of supplying this energy, and by increasing it sufficiently not only are molecules drawn apart and most solids converted into fluids and finally into gases, but there is reason to believe that at extremely high temperatures, such as may prevail in the sun, all matter would be resolved into isolated or dissociated atoms. Thus, water at a temperature of 1,200° is resolved into a mixture of oxygen and hydrogen atoms no longer chemically united into water-molecules; and iodine-vapour, which below 700° degrees consists of molecules of two atoms, above that temperature consists of single atoms only.

The subject might be pursued further, but enough has been said for the present purpose to show that the universe consists of atoms which are endowed with polarity, and that as diminished temperature allows these atoms to come closer together and form compounds, matter in all its forms is built up by the action of polar forces.

CHAPTER VI.
POLARITY IN LIFE.

Contrast of living and dead—Eating and being eaten—Trace matter upwards and life downwards—Colloids—Cells—Protoplasm—Monera—Composition of protoplasm—Essential qualities of life—Nutrition and sensation—Motion—Reproduction—Spontaneous generation—Organic compounds—Polar conditions of life.

Polarity having been established as the universal law of the inorganic world, we have now to pass to the organic, or world of life. At first sight there seems to be a great gulf fixed between the living and the dead which no bridge can span. But first impressions are very apt to deceive us, and when things are traced up to their origins we often find them getting nearer and nearer until it is difficult to say where one begins and the other ends. Take for instance such an antithesis as ‘eating or being eaten.’ If a hunter meets a grizzly bear in the Rocky Mountains, one would say that no distinction can be sharper than whether the bear eats the man, or the man the bear. In the one case there is a man, and in the other a bear, less in the world. But look through a microscope at a glass of water, and you may see two specks of jelly-like substance swimming in it. They are living creatures, for they eat and grow, and thrust out and retract processes of their formless mass, which serve as temporary legs and arms for seizing food and for voluntary motion. In short, they are each what may be called strictly individual amœbæ, forming separate units of the animated creation as much as the man and the bear. But if the two happen to come in contact, what happens? The two slimy masses involve one another and coalesce, and the resulting amœba swims away merrily as two gentlemen rolled into one.

Now in his case what became of their individualities: did amœba A eat amœba B, or vice versâ, and is the resulting amœba a survival of A or of B, or of both or neither of them? And what becomes of the antithesis of ‘eating or being eaten’ which was so clear and distinct in the highly specialised forms of life, and is so evanescent in the simpler forms? This illustration may serve to teach us how necessary it is to trace things up to their origins, before expressing too trenchant and confident opinions as to their nature and relations.

In the case of the organic and inorganic worlds the proper course obviously is, not to draw conclusions from extreme and highly specialised instances, but to follow life downwards to its simplest and most primitive form, and matter upwards to the form which approaches most nearly to this form of life. Following matter upwards, we find a regular progression from the simple to the complex. Take the diamond, which is one of the simplest of substances, being merely the crystallised form of a single ultimate element, carbon. It is extremely hard and extremely stable. Ascending to compounds of two, three, or more elements, we get substances which are more complex and less stable; and at last we arrive at combinations which involve many elements and are extremely complex. Among these latter substances are some, called colloids, which are neither solid, like crystals, nor fluid, like liquids, but in an intermediate state, like jelly or the white of an egg, in which the molecules have great mobility and are at a considerable distance apart, so that water can penetrate their mass. These colloids are for the most part very complicated compounds of various elements based on a nucleus of carbon, which, from its atom having four poles with strong mutual attractions, is eminently qualified for forming what may be called the inner skeleton of these complex combinations. Colloids of this description form the last stage of the ascending line from inorganic matter to organic life.

Next let us trace life downwards towards matter. There is a constant succession from the more to the less complex and differentiated: from man, through mammals, reptiles, fishes, and a long chain of more simple forms, until at its end we come to the two last links, which are the same for all animals, all plants, and all forms of animated existence. The last link but one is the cell, the last of all is protoplasm.

Protoplasm, or, as Huxley calls it, ‘the physical basis of life,’ is a colourless jelly-like substance, absolutely homogeneous, without parts or structure, in fact a mere microscopic speck of jelly.

The cell is the first step in the specialisation of protoplasm, the outer layer of which, in contact with the surrounding environment, becoming hardened so as to form an enclosing cell-wall, while a portion of the enclosed protoplasm condenses into a nucleus, in which a further condensation makes what is called the nucleolus or second smaller nucleus. This constitutes the nucleated cell, whose repeated subdivision into other similar cells in geometrical progression furnishes the raw material out of which all the varied structures of the world of life are built up. Plants and animals, bones, muscles, and organs of sense, are all composed of modified cells, hardened, flattened, or otherwise altered, as the case may require. If we trace life up to its origin in the individual instead of in the species, we arrive at the same result. All plants and animals, whether of the lowest or highest forms, fish, reptile, bird, mammal, man, begin their individual existence as a speck of protoplasm, passing into a nucleated cell, which contains in it the whole principle of its subsequent evolution into the mature and completed form.

Protoplasm is, therefore, evidently the nearest approach of life to matter; and if life ever originated from atomic and molecular combinations, it was in this form. To suppose that any more complex form of life, however humble, could originate from chemical combinations, would be a violation of the law of evolution, which shows a uniform development from the simple to the complex, and never a sudden jump passing at a bound over intermediate grades. To understand life, therefore, we must understand protoplasm; for protoplasm, closely as it approximates to colloid matter, is thoroughly alive. A whole family, the Monera, consist simply of a living globule of jelly, which has not even begun to be differentiated. Every molecule, as in a crystal, is of homogeneous chemical composition and an epitome of the whole mass. There are no special parts, no organs told off for particular functions, and yet all life-functions—nutrition, reproduction, sensation, and movement—are performed, but each by the whole body. The jelly-speck becomes a mouth to swallow, and turning inside out, a stomach to digest. It shoots out tongues of jelly to move and feel with, and presently withdraws them.

With these attributes it is impossible to deny to protoplasm the full attributes of life, or to doubt that, like the atom in the material world, it is the primary element of organic or living existence. Given the atom, we can trace up, step by step, the whole evolution of matter; so given the protoplasm, we can trace up the evolution of life by progressive stages to its highest development—man. To understand life, therefore, we must begin by trying to understand protoplasm.

What is protoplasm? In its substance it is a nitrogenous carbon compound, differing only from other similar compounds of the albuminous family of colloid by the extremely complex composition of its atoms. It consists of five elements, and its average composition is said by chemists to be 52·55 per cent. carbon, 21·23 oxygen, 15·17 nitrogen, 6·7 hydrogen, 1·2 sulphur. Its peculiar qualities, therefore, including life, are not the result of any new and peculiar atom added to the known chemical compounds of the same family, but of the manner of grouping and motions of these well-known material elements. It has in a remarkable degree the faculty of absorbing water, so that its molecules seem to float in it in a condition of semi-fluid aggregation, which seems to be necessary for the complex molecular movements which are the cause or accompaniment of life. Thus, many seeds and animalculæ, if perfectly dry, may remain apparently as dead and as unchanging as crystals, for years, or even, as in the case of the mummy wheat, for centuries, to revive into life when moistened.

But in addition to those material qualities in which protoplasm seems to differ only from a whole group of similar compounds of the type of glycerine, by the greater complexity and mobility of its molecules, it has developed the new and peculiar element which is called life. Life in its essence is manifested by the faculties of nutrition, sensation, movement, and reproduction.

As regards nutrition there is this essential difference between living and non-living matter. The latter, if it feeds and grows at all, does so only by taking on fresh molecules of its own substance on its outer surface, as in the case of a small nucleus-crystal of ice in freezing water. If it feeds on foreign matter and throughout its mass, it does so only in the way of chemical combination, forming a new product. Living matter, on the other hand, feeds internally, and works up foreign substances, by the process we call digestion, into molecules like its own, which it assimilates, rejecting as waste any surplus or foreign matter which it cannot incorporate. It thus grows and decays as assimilation or waste preponderates, remaining always itself. The distinction will be clear if we consider what happens when water rusts iron. In a certain sense the iron may be said to eat the oxygen, reject the hydrogen, and grow, or increase in weight by what it feeds on; but the result is not a bigger piece of iron, but a new substance, rust, or oxide of iron. That living matter should feed internally is not so wonderful, for its semi-fluid condition may well enable foreign molecules to penetrate its mass and come in contact with its own interior molecules; but it is an experience different from anything known in the inorganic world that it should be able to manufacture molecules of protoplasm like its own out of these foreign molecules, and thus grow by assimilation. For instance, when amœbæ, bacteria, and other low organisms live and multiply in chemical solutions which contain no protoplasm, but only inorganic compounds containing the requisite atoms for making protoplasm, or when a plant not only chemically decomposes carbonic dioxide, exhaling the oxygen and depositing the carbon in its stem and leaves, but also from this and other elements drawn from the soil or air manufactures the living protoplasm which courses through its channels, the result is that life has manufactured life out of non-living materials.

If we take sensation, this, in its last analysis, is change, or molecular motion, induced in a body by the action of its environment. Here there is a certain analogy between living and non-living matter, for the latter does respond to changes in the surrounding environment, as in the case of heat, electricity, and otherwise; but living matter is far more sensitive, the changes are far more frequent and complex, and in certain cases they are accompanied by a sensation of what is called consciousness, which in the higher organisms rises into a perception of voluntary effort or free-will as a factor in the transformation of energies. Thus it happens that in the case of dead matter the changes produced by a change of conditions follow fixed laws and can be predicted and calculated, while those of living matter are apparently uncertain and capricious. We can tell how much an iron bar will expand with heat; but we cannot say whether, if a particle of food is brought within reach of an amœba, it will or will not shoot out a finger to seize it. If the amœba is hungry it probably will; if it is enjoying a siesta after a full meal, it probably will not.

The case of sensation includes that of motion, which is after all only sensation applied in the liberation of energy of position which has by some chemical process become stored up, either in the living mass, or in some special organ of it, such as muscle. Iron, for instance, moves when it expands by heat or is attracted by a magnet; but it moves, like the planets, by fixed and calculable laws: while living matter moves, as might be expected from the variable character of its sensation, in a manner which often cannot be calculated. There are cases, however, of reflex or involuntary motion, where, even in the highest living organisms, sensation and motion seem to follow change of environment, in a fixed and invariable sequence, as in shrinking from pain, touching or galvanising a nerve; and it may be that the apparent spontaneousness and variability of living motion is only the result of the almost infinitely greater complexity and mobility of the elements of living matter.

Reproduction remains, which is the faculty most characteristic of life, and which distinguishes most sharply the organic from the inorganic world. In the inorganic there is no known process by which dead matter reproduces itself, as the cell does when it contracts in the middle and splits up into two cells, which in their turn propagate an endless number of similar cells, increasing in geometrical progression until they supply the raw material from which all the countless varieties of living organisms are built up, which, in their turn, repeat the process and reproduce themselves in offspring. This is the real mystery of life; we can partly see or suspect how its other faculties might arise from an extension of the known qualities and laws of matter and of energy; but we can discern no analogy between the non-reproductive nitrogenous carbon compound, which makes so near an approach to protoplasm in its chemical composition, and the reproductive protoplasm, which is fertile, increases and multiplies, and replenishes the earth. Can the gap be bridged over: can protoplasm be manufactured out of chemical elements? It is done every day by plants which make protoplasm out of inorganic elements, and by the lowest forms of life which live and multiply in chemical solutions. It is done also in the life-history of all individuals whose primitive cell or ovum makes thousands or millions of other cells, each containing within its enclosing membrane as much protoplasm as there was in the unit from which they started. But in all these instances there was the living principle to start with, existing in the primitive speck of protoplasm, from which the rest were developed. Can this primitive speck be created; or, in other words, can protoplasm be artificially manufactured by chemical processes?

The answer must be, No; not by any process now known. The similarity of chemical composition, and the increasing conviction of the universality of natural law and of evolution, have led to a very general belief that such a spontaneous generation of life must be possible, and numerous experiments have been made to produce it. For a time the balance seemed to be very evenly held between the supporters and opponents of spontaneous generation. In fact, starting from the assumption, which at first was common to both sides, that heat equal to the boiling point of water destroyed all life organisms, spontaneous generation had the best of it: for it was clearly proved that living organisms did appear in infusions contained in vessels which had been hermetically sealed, after being subjected to this, or even a higher degree of heat. But subsequent and more careful experiments have shown that the germs or spores of bacteria and other animalculæ, which are generally floating in the air, can, when dry, withstand a greater degree of heat, and that when the experiments are made in optically pure air no life ever appears and the infusions never putrefy. On questions of this sort all who are not themselves expert experimentalists must be guided by authority, and we may be content to accept the dictum of Huxley that biogenesis, or all life from previous life, was ‘victorious along the whole line.’ But in doing so we must accept Huxley’s caution, ‘that with organic chemistry, molecular physics, and physiology yet in their infancy, and every day making prodigious strides, it would be the height of presumption for any man to say that the conditions under which matter assumes the qualities called vital, may not some day be artificially brought together.’

And further, ‘that as a matter not of proof but of probability, if it were given me to look beyond the abyss of geologically recorded time, to the still more remote period when the earth was passing through chemical and physical conditions which it can never see again, I should expect to be a witness of the evolution of living protoplasms from non-living matter.’ Such is the cautious candour with which scientific men approach problems upon which theologians dogmatise with the unerring intrepidity of ignorance.

In the meantime what may be said as to Huxley’s reservations is this: A considerable step has been made in the direction indicated, by the success of recent chemistry in forming artificially what are called organic compounds, that is, substances which were previously known only as products of animal or vegetable secretions. Urea, for instance, the base of uric acid, with which so many are unfortunately familiar in the form of gout; indigotine, the principle of the blue colouring matter of the indigo plant; and alizarine, that of madder; are all now produced artificially, and have even become important articles of commerce. If chemists can make the indigotine, which the growing plant elaborates at the same time as it elaborates protoplasm, may we not hope some day to make the latter as well as the former product? Now organic compounds of this class are being formed artificially every day, and it is said that chemists have already succeeded in producing several hundreds. But even if this expectation is never fulfilled, we may fall back on Huxley’s second reservation of the enormous difference of chemical and physical conditions in the early stages of the earth’s life from anything now known. It has been calculated that the earth’s temperature when it first started on its career as an independent planet was something like 3,000,000° Fahrenheit. At this heat probably all atoms would be dissociated; but as the temperature diminished they would come closer together, but still with a great deal of motion, and making wide excursions, which might bring many different atoms together in complex though unstable combinations. Moreover, carbon, which is the basis of all such combinations of the class of protoplasm, was far more abundant in those early days in the form of carbonic dioxide gas, before the enormous amount of vegetable matter in the form of coal and otherwise, had been subtracted from it. In any case the first protoplasm must be extremely ancient, for the remains of sea-weeds are found in the oldest strata, and vegetation of any sort implies the manufacture of protoplasm from inorganic matter.

The passage from the organic into the inorganic world is best traced by following the line of Pasteur’s researches on ferments. How does the world escape being choked up by the accumulation of dead organic matter throughout innumerable ages? By what are called ferments, inducing processes of fermentation and putrefaction, by which the course of life is reversed, and the organic elements are taken to pieces and restored to the inorganic world. Pasteur proved, in opposition to the theories of Liebig and other older chemists, that this was not done directly by the oxygen of the air, but through the intermediate agency of living microbes, whose spores, floating in the air, took up their abode and multiplied wherever they found an appropriate habitation. Given an air purified from germs, or a temperature low enough to prevent them from germinating, and putrescible substances would keep sweet for ever. The practical realisation of this is seen in the enormous commerce in canned meats and fruits, and in the imports of frozen beef and mutton, causing a fall of rents and much lamentation among British landlords and farmers.

But then the question was asked, How are your microscopic organisms disposed of? What are the ferments of your ferments? For even microscopic bacteria and vibrios would, in time, choke up the world by their residue if not got rid of. Pasteur answered that the ferments are destroyed by a new series of organisms—aerobes—living in the air, and these by other aerobes in succession until the ultimate products are oxidised. ‘Thus, in the destruction of what has lived, all is reduced to the simultaneous action of the three great natural phenomena—fermentation, putrefaction, and slow combustion. A living being, animal or vegetable, or the débris of either, having just died, is exposed to the air. The life that has abandoned it is succeeded by life under other forms. In the superficial parts, accessible to the air, the germs of the infinitely little aerobes flourish and multiply. The carbon, hydrogen, and nitrogen of the organic matter are transformed by the oxygen of the air, and under the vital activity of the aerobes, into carbonic acid, the vapour of water, and ammonia. The combustion continues as long as organic matter and air are present together. At the same time the superficial combustion is going on, fermentation and putrefaction are performing their work in the midst of the mass by means of the developed germs of the original microbes, which, note, do not need oxygen to live, but which oxygen causes to perish. Gradually the phenomena of destruction are at last accomplished through the work of latent fermentation and slow combustion.’

This seems a complete demonstration of the passage of the organic into the inorganic world in the way of analysis, or taking the puzzle to pieces. In the opposite way of synthesis, or putting it together, the nearest approach yet made has been in the manufacture of those organic compounds already referred to, such as urea, alizarine, indigotine and other products which had hitherto only been known as products of animal or vegetable life. Of these a vast number have been already formed from inorganic elements by chemical processes, and almost every day announces some fresh discovery.

Under these circumstances it is unsafe to affirm either, on the one hand, that the problem has been solved and that life has ever been made in a laboratory; or, on the other hand, that there is any such great gulf fixed between the organic and the inorganic, that we can assume a break requiring secondary supernatural interference to surmount it, and ignore the good old maxim that ‘Natura nihil facit per saltum.’ Positive proof is wanting, but the probabilities point here, as they do everywhere else throughout the universe, to the truth of the theory of ‘original impress’ as opposed to that of ‘secondary interference.’

It remains to show how the fundamental law of polarity affects the more complex relations of life and of its various combinations. And here it is important to bear in mind that as the factors of the problem become more intricate and complex, so also do the laws which regulate their existence and action. Polarity is no longer a simple question of attraction and repulsion at the two ends of a magnet or at the opposite poles of an atom. It appears rather as a general law under which as the simple and absolute becomes differentiated by evolution into the complex and manifold, it does so under the condition of developing contrasts. For every plus there is a minus, for every like an unlike; one cannot exist without the other; and, although apparently antagonistic, harmonious order is only possible by their co-existence and mutual balance.

This is so important that it may be well to make the idea clearer by an illustration. The earth revolves round the sun in its annual orbit under the influence of two forces: the centripetal, or force of gravity tending to draw it towards the sun; and the centrifugal, tending to make it dart away into infinite space. During half the orbit the centripetal seems to be gaining ground on the centrifugal, and the earth is approaching nearer to the sun. If this continued it would revolve ever nearer and soon fall into it; but the centrifugal force is gradually recruiting its strength from the increased velocity of the earth, until it first equals the centripetal, and finally outstrips it, and for the remaining half of the orbit it is constantly gaining ground. If this went on, the earth would fly off into the chilly regions of outer space; but the centripetal force in its turn regains the ascendency; and thus by the balance of the two forces our planet describes the beautiful ellipse, its harmonious orbit as a habitable globe; while comets in which one or the other force unduly preponderates for long periods are alternately drawn into fiery proximity to the sun, and sent careering through regions void of heat.

Compare this passage from Herbert Spencer: ‘As from antagonist physical forces, as from antagonist emotions in each man, so from the antagonist social tendencies man’s emotions create, there always results not a medium state, but a rhythm between opposite states. The one force or tendency is not continuously counterbalanced by the other force or tendency; but now the one greatly preponderates, and presently by reaction there comes a preponderance of the other.’

And again: ‘There is nowhere a balanced judgment and a balanced action, but always a cancelling of one another by opposite errors. Men pair off in insane parties, as Emerson puts it.’

The reader will now begin to understand the sense in which polarity applies to these complex conditions of an advanced evolution.

To return, however, from this digression to the point at which it began, viz. the origin of life, we have to show how the law of polarity prevails in the organic as well as in the inorganic world. In the first place the material to which all life is attached, from the speck of protoplasm to the brain of man, is strictly a chemical product of atoms and molecules bound together by the same polar laws as those of inorganic matter.

In like manner all the essential processes by which life lives, moves, and has its being, are equally mechanical and chemical. If the brain, receiving a telegram from without through the optic nerve, sends a reply along another nerve which liberates energy stored up in a muscle and produces motion, the messages are received and transmitted like those sent by a voltaic battery along the wires of a telegraph, and the energy is stored up by the slow combustion of food in oxygen, just as that of the steam-engine is produced by the combustion of coal. All this is mechanical, inorganic, and therefore polar.

But when we come to the conditions of life proper, we find the influence of polarity mainly in this: that as it develops from simpler into more complex forms, it does so under the law of developing contrasts or opposite polarities, which are necessary complements of each other’s existence. Thus, as we ascend in the scale of life, we find two primitive polarities developed: that of plant and animal, and that of male and female.

CHAPTER VII.
PRIMITIVE POLARITIES—PLANT AND ANIMAL.

Contrast in developed life—Plants producers, animals consumers—Differences disappear in simple forms—Zoophytes—Protista—Nummulites—Corals—Fungi—Lichens—Insectivorous plants—Geological succession—Primary period, Algæ and Ferns—Secondary period, Gymnosperms—Tertiary and recent, Angiosperms—Monocotyledons and Dicotyledons—Parallel evolution of animal life—Primary, protista, mollusca, and fish—Secondary, reptiles—Tertiary and recent, mammals.

Animals or plants? Judging by first impressions, nothing can be more distinct. No one, whether scientific or unscientific, could mistake an oak tree for an ox. To the unscientific observer the tree differs in having no power of free movement, and apparently no sensation or consciousness; in fact, hardly any of the attributes of life. The scientific observer sees still more fundamental differences, in the fact that the plant feeds on inorganic ingredients, out of which it manufactures living matter, or protoplasm; while the animal can only provide itself with protoplasm from that already manufactured by the plant. The ox, who lives on grass, could not live on what the grass thrives on, viz. carbon, oxygen, hydrogen, and nitrogen. The contrast is so striking that the vegetable world has been called the producer, and the animal world the consumer, of nature.

Again, the plant derives the material framework of its structure from the air, by breathing in through its leaves the carbonic dioxide present in the atmosphere, decomposing it, fixing the carbon in its roots, stem, and branches, and exhaling the oxygen. The animal exactly reverses the process, inhaling the oxygen of the air, combining it with the carbon of its food, and exhaling carbonic dioxide. Thus, a complete polarity is established, as we see in the aquarium, where plant and animal life balance each other, and the opposites live and thrive, where the existence of either would be impossible without the other.

Sharp, however, as the contrast appears to be in the more specialised and developed specimens of the two worlds, we have here another instance of the difficulty of trusting to first impressions, and have to modify our conceptions greatly, if we trace animal and vegetable life up to their simplest forms and earliest origins. In the first place, each individual vegetable or animal begins its existence from a simple piece of pure protoplasm. This develops in the same way into a nucleated cell, by whose repeated subdivision the raw material is provided for both structures alike. The chief difference at this early stage is that the animal cells remain soft and naked, while those of vegetables secrete a comparatively solid cell-wall, which makes them less mobile and plastic. This gives greater rigidity to the frame and tissues of the plant, and prevents the development of the finer organs of sensation and other vital processes, which characterise the animal. But this is a difference of development only, and the origination of the future life from the speck of protoplasm is the same in both worlds.

If, instead of looking at the origin of individuals, we trace back the various forms of animal and vegetable life from the more complex to the simpler forms, we find the distinctions between the two disappearing, until at last we arrive at a vanishing point where it is impossible to say whether the organism is an animal or a plant.

A whole family, comprising sponges, corals, and jelly-fish, are called Zoophytes, or plant-animals, from the difficulty of assigning them to one kingdom or the other. On the whole they rather more resemble animals, and are generally classed with them, though they lack many of their most essential qualities, and in form often bear a close resemblance to plants. But when we descend a step lower in the scale of existence we come to a large family—the Protista—of which it is impossible to say that they are either plants or animals. In fact, scientific observers have classed them sometimes as belonging to one and sometimes to the other kingdom; and it was an organism of this class, looking at which through a microscope Huxley pronounced it to be probably a plant, while Tyndall exclaimed that he would as soon call a sheep a vegetable. They are mostly microscopic, and are the first step in organised development from the Monera, which are mere specks of homogeneous protoplasm. Small as they are they have played an important part in the formation of the earth’s crust, for the little slimy mass of aggregated cells has in many instances the power of secreting a solid skeleton, or a minute and delicate envelope or shell, the petrified remains of which form entire mountains. Thus the nummulitic limestone, which forms high ranges on the Alps and Himalayas, and of which the Pyramids are built, consists of the petrified skeletons of a species of Radiolaria, or many-chambered shells, forming the complicated and elegant mansion with many rooms and passages, of the formless, slimy mass which constitutes the living organism. Chalk also, and the chalk-like formation which is accumulating at the bottom of deep oceans, are the results of the long-continued fall of the microscopic snowdrift of shells of the Globigenera and other protistic forms swimming in the sea; and in a higher stage of development the skeletons of corals, one of the family of Zoophytes or plant-animals, form the coral reefs and islands so numerous in the Pacific and Indian Oceans, and are the basis of the vast masses of coralline limestone deposited in the coal era and other past geological periods.

As development proceeds the distinction between plants and animals becomes more apparent, though even here the simplest and earliest forms often show signs of a common origin by interchanging some of the fundamental attributes of the two kingdoms. Thus, the essential condition of plant existence is to live on inorganic food, which they manufacture into protoplasm, by working up simple combinations into others more complicated. Their diet consists of water, carbonic dioxide, and ammonia; they take in carbonic dioxide and give out oxygen, while animals do exactly the reverse. But the fungi live, like animals, upon organic food consisting of complicated combinations of carbon, which they assimilate; and, like animals, they inhale oxygen and give out carbonic dioxide.

Lichens afford a very curious instance of the association of vegetable and animal functions in the same plant. They are really formed of two distinct organisms: a body which is a low form of Alga or sea-weed, and a parasitic form of fungus, which lives upon it. The former has a plant life, living on inorganic matter and forming the green cells, or chlorophyll, which are the essential property of plants, enabling them under the action of the sun’s rays to decompose carbonic dioxide; while the parasite lives like an animal on the formed protoplasm of the parent stem, forming threads of colourless cells which envelop and interlace with the original lichen of which they constitute the principal mass, as in a tree overgrown with ivy.

Even in existing and highly developed plants we find some curious instances of reversion towards animal life. Certain plants, for instance, like the Dionæa or Venus’ fly-trap, finding it difficult to obtain the requisite supply of nitrogenous food in a fluid state from the arid or marshy soil in which they grow, have acquired a habit of supplying the deficiency by taking to an animal diet and eating flies. Conjoined with this is a more highly developed sensitiveness, and power of what appears to be voluntary motion, and a faculty of secreting a sort of gastric juice in which the flies are digested. The fundamental property also of decomposing carbonic dioxide and exhaling oxygen depends on light stimulating a peculiar chemical action of the chlorophyll, and at night leaves breathe like lungs, exhaling not oxygen, but the carbonic dioxide.

The records of geology, imperfect as they are, show a continued progression from these simple and neutral organisms to higher and more differentiated forms, both in the animal and vegetable worlds. These records are imperfect because the soft bodies of the simpler and for the most part microscopic forms of protoplasm and cell life are not capable of being preserved in petrifactions, and it is only when they happen to have secreted shells or skeletons that we have a chance of identifying them. Still we have a sufficient number of remains in the different geological strata to enable us to trace development. Thus, in the vegetable world, in the earliest strata, the Laurentian, Cambrian, and Silurian, forming the primordial period, which forms a thickness of some 70,000 feet of the earth’s crust—or more than that of the whole of the subsequent strata, Primary, Secondary, Tertiary, and Quaternary, taken together—we find only vegetable remains of the lowest group of plants, that of the Tangles or Algæ, which live in water. Forests of these sea-weeds, like those of the Aleutian Islands, in some of which single tangles stream to the length of sixty feet, and floating masses, like those of the Sargasso Sea, appear to have constituted the sole vegetation of these primæval periods.

The Primary epoch, which comes next, comprises the Devonian or Old Red Sandstone, the Carboniferous or Coal system, and the Permian, the average thickness of the three together amounting to about 42,000 feet. In these the family of Ferns predominates, the remains of which constitute the bulk of the large strata of coal, forming in modern times our great resource for obtaining the energy which, in a transformed shape, does so much of our work. Pines begin to appear, though sparingly, in this epoch.

The Secondary epoch comprises the Triassic, the Jurassic, and the Cretaceous or Chalk formation, the average thickness of the three amounting to about 15,000 feet. In this era a higher species of vegetation predominates, that of the Gymnosperms, or plants having naked seeds, of which the pines, or Coniferæ, and the palm-ferns, or Cycadeæ, are the two principal classes. As in the case of the former epoch, traces of the approaching higher organisation in the form of leaf-bearing trees began to appear towards its close.

The Tertiary period extends from the end of the Chalk to the commencement of the Quaternary or modern period. It is divided into the Eocene or older, the Miocene or middle, and the Pliocene or newest Tertiary system; though the division is somewhat arbitrary, depending on the number of existing species, mostly of shellfish, which have been found in each. The average thickness of the three together is about 3,000 feet. In this formation a still higher class of vegetation of the same order as that now existing, which made its first appearance in the Chalk period, has become predominant. It is that of Angiosperms, or plants with covered seeds, forming leafy forests of true trees. This group is divided into the two classes of monocotyledons or single-seed-lobed plants, and dicotyledons or plants with double seed-lobes. The monocotyledons spring from a single germ leaf, and are of simpler organisation than the other class. They comprise the grasses, rushes, lilies, irids, orchids, sea-grasses, and a number of aquatic plants, and in their highest form develop into the tree-like families of the palms and bananas.

The dicotyledons include all forms of leaf-bearing forest trees, almost all fruits and flowers, in fact by far the greater part of the vegetable world familiar to man, as coming into immediate relation with it, except in the case of the cultivated plants, which are developments of the monocotyledon grasses.

We see, therefore, in the geological record a confirmation of the evolution over immense periods of time of the more complex and perfect from the simple and primitive.

If we turn to the same geological record to trace the development of animal life, we find it running a parallel course with that of plants. The earliest known fossil, the Eozoon Canadiense, from the Lower Laurentian, is that of the chambered shell of a protista of the class of Rhizopods, whose soft body consists of mere protoplasm which has not yet differentiated into cells. As we ascend the scale of the primordial era, traces of marine life of the lower organisms begin to appear, until in the Silurian they become very abundant, consisting however mainly of mollusca and crustacea, and in the Upper Silurian we find the first traces of fishes.

In the Primary era the Devonian and Permian formations are characterised by a great abundance of fishes, of the antique type, which has no true bony skeleton, but is clothed in an armour of enamelled scales, and whose tail, instead of being bi-lobed or forked, has one lobe only—a type of which the sturgeon and garpike are the nearest surviving representatives. In the Coal formation are found the first remains of land animals in the form of insects and a scorpion, and a few traces of vertebrate amphibious animals and reptiles; while higher up in the Permian are found a few more highly developed reptiles, some of which approximate to the existing crocodile. Still fishes greatly predominate, so that the whole Primary period may be called the age of fishes, as truly as, looking at its flora, it may be called the age of ferns.

In the Secondary period reptiles predominate, and are developed into a great variety of strange and colossal forms. The first birds appear, being obviously developed from some of the forms of flying lizards, and having many reptilian characters. Mammals also put in a first feeble appearance, in the form of small, marsupial, insectivorous creatures.

In the Tertiary period the class of mammals greatly predominates over all other vertebrate animals, and we can see the principal types slowly developing and differentiating into those at present existing. The human type appears plainly in the middle Miocene, in the form of a large anthropoid ape, the Dryopithecus, and undoubted human remains are found in the beginning of the Quaternary, if not, as many distinguished geologists believe, in the Pliocene and even in the Miocene ages.

So far, therefore, there seems to be a complete parallelism between the evolution of animal and vegetable life from the earliest to the latest, and from the simplest to the most complex forms. These facts point strongly to a process of evolution by which the animal and vegetable worlds, starting from a common origin in protoplasm, the lowest and simplest form of living matter, have gradually advanced step by step, along diverging lines, until we have at last arrived at the sharp antithesis of the ox and the oak tree. It is clear, however, that this evolution has gone on under what I have called the generalised law of polarity, by which contrasts are produced of apparently opposite and antagonistic qualities, which however are indispensable for each other’s existence. Thus animals could not exist without plants to work up the crude inorganic materials into the complex and mobile molecules of protoplasm, which are alone suited for assimilation by the more delicate and complex organisation of animal life. Plants, on the other hand, could not exist without a supply of the carbonic dioxide, which is their principal food, and which animals are continually pouring into the air from the combustion of their carbonised food in oxygen, which supplies them with heat and energy. Thus nature is one huge aquarium, in which animal and vegetable life balance each other by their contrasted and supplemental action, and, as in the inorganic world, harmonious existence becomes possible by this due balance of opposing factors.

CHAPTER VIII.
PRIMITIVE POLARITIES—POLARITY OF SEX.