ART. III. THE ATOMIC THEORY.

1. Lucretius. De rerum natura. Ed. H. A. J. MUNRO. (Cambridge, 1864.)

2. The Conservation of Energy. By BALFOUR STEWART. (London, 1874.)

3. Lucretius and the Atomic Theory. By JOHN VEITCH. (Glasgow, 1875.)

4. Encyclopædia Britannica. Article 'Atom,' by JAMES CLERK MAXWELL.

(Edinburgh, 1875.) 5. The Unseen Universe. (London, 1875.)

6. History of Materialism. By F. A. LANGE. Translated by E. C. THOMAS. (London, 1877.)

7. Lectures and Essays. By W. K. CLIFFORD. Edited by L. STEPHEN and F. POLLOCK. (London, 1879.)

8. Fragments of Science. By JOHN TYNDALL. (London, 1879.) 9. Life of Fames Clerk Maxwell. By LEWIS CAMPBELL and WILLIAM GARNETT. (London, 1882.)

10. The Atomic Theory of Lucretius contrasted with Modern Doctrines of Atoms and Evolution. By JOHN MASSON. (London, 1884.)

ATTEMPTS have been made, both in ancient and modern times, to explain the origin of the material universe. The ultimate nature of matter was a subject of speculation with the Greek philosophers. Their views were borrowed and more fully developed by later Roman thinkers, whose fetches from the deep arcana of nature were often marvellous. Their speculative guesses have in many cases been proved by the researches of modern science to have a foundation in truth. In one case, an ancient theory has come to be recognized by most scientific men as embodying the principle which has led to many important discoveries in recent times. Of those which have come down from antiquity, two only are deserving of notice, one being the doctrine of the infinite divisibility of matter, and the other the protest against it, known as the atomic theory The oμoloμépia (or likeness of parts to the whole) of Anaxagoras and the Peripatetics, was the assertion of the principle that a particle of matter can be subdivided indefinitely, at least in imagination, after the actual operation has become impossible owing to the weakness of the senses, and that earth, if so subdivided as long as it was visible, would always be earth; and so of every other substance.

VOL. XXII.—NO. XLIII.

F

The authors of The Unseen Universe point out that, if this theory be correct, matter must be practically continuous but intensely heterogeneous, and that if the heterogeneity were sufficiently marked, the laws of gravitation would be capable of accounting for at least the greater number of effects at present attributed to molecular forces. In the latter case the law of gravity would still have to be accounted for. Others denied that the continual subdivision was possible, and hence arose the atomic theory. They said that matter, after being subdivided a certain number of times, although the parts might become so small as to be beyond the grasp of the senses, would ultimately be impenetrable, no longer divisible, hard in solid singleness, and aтоμol, or that which cannot be cut. The two theories were therefore in direct opposition to each other.

It was the opinion of the late Professor Clerk Maxwell that they took their origin from the speculations of the philosophers about number and continuous magnitude. The first exact notions of quantity were founded on considerations of number which is discontinuous, because it is only possible to pass from one to another per saltum, while geometrical magnitudes are continuous. The attempt to apply numerical methods to the latter led them to the doctrine of the infinite divisibility of space and time. A similar process of reasoning was easily applied to matter. If it is extended and fills space, the same mental operation which recognizes the divisibility of space, is capable of application to the matter which occupies it. From this point of view the atomic theory might be regarded as the old numerical way of conceiving magnitude, while the opposite doctrine of the infinite divisibility of matter might appear the most scientific. The atomists maintained the distinction between matter and space; atoms, according to them, not filling the universe, because there is void between them. Their opponents held that there was no vacuum, because all space was filled with matter. In recent times, those who hold the atomic theory believe in the continuity of matter and a plenum, so that in this respect they are at variance with its ancient supporters.

Professor Veitch is of opinion that there is no necessary incompatibility between the atomic theory and the doctrine of the infinite divisibility of matter. As, on the former theory, it must at a certain point necessarily retain length and breadth, to say that it is still indivisible, is contradictory. Replying to the difficulty, he argued that matter, up to a certain point, might be qualitatively but not quantitatively indivisible. In

the former case, no possible analysis, real or in conception, could get out of it anything but one homogeneous unity, in the sense of its quality or definite nature. If this reasoning be sound, there is no real incompatibility between the doctrine of the ultimate divisibility of matter, and the theory of the atomists. To suppose that the final elements of a body are absolutely impenetrable, and that they are at the same time capable of being infinitely divided in thought, does not seem to him to be necessarily antagonistic to the atomic theory, if the conception of qualitative indivisibility be retained. The ideal divisibility of anything occupying space is always possible, but this is not repugnant to the notion of the impossible division of the integrity of its quality. To the same purport Maxwell said that he did not assert that there was an absolute limit to the divisibility of matter. What he asserted was, that after a body had been divided into a certain finite number of constituent parts, called molecules, any further division of them would deprive them of the properties which gave rise to the phenomena observed in the substance.

The germ of the atomic theory was first stated by Leucippus, a contemporary of Anaxagoras, about B.C. 400. It was taught fifty years afterwards by Democritus, whom Bacon regards as the most scientific of the ancient philosophers, and nearly a century later was more fully developed by Epicurus. The theory was ridiculed and rejected by Aristotle, and nearly all the Greek philosophers, but it seems to have proved attractive to the Roman intellect. The writings of those who held it prior to the age of Lucretius, who died B.C. 55, are lost, so that the only remaining source from whence authentic information can be obtained about it is his poem De rerum natura. Bacon, in his treatise De principiis et originibus, said that Democritus was a greater man than Plato or Aristotle, although their philosophy was noised and celebrated in the schools, amid the din and pomp of professors. It was not they, according to him, but the barbarians Genseric and Attila who destroyed the atomic philosophy, because at the time when all human learning had suffered shipwreck, the planks of the Aristotelian and Platonic philosophy, being lighter and of a more inflated substance, were preserved and transmitted to posterity, while the more solid parts sank and almost passed into oblivion. The atomic theory remained in abeyance till Gassendi rescued it from oblivion, and showed that it afforded the true basis for the scientific study of nature. Subsequently, in the hands of Dalton, who found out the chemical law of multiple proportions, it led to other important discoveries in

the domain of molecular physics, and is now adopted by nearly all scientific men. Professor Huxley has said that if there is one thing clear about the progress of modern science, it is the tendency to reduce all scientific problems, except those that are purely mathematical, to problems in molecular physics that is to say, to attractions, repulsions, motions and co-ordination of the ultimate particles of matter. The atomic theory is therefore leading to discoveries in science, of which Lucretius, with all his deep insight into nature, could not have formed any conception. Criticizing these speculations, the authors of The Unseen Universe say that they represent the most plausible guesses yet propounded as to the ultimate nature of matter.

The ancient atomists anticipated, however darkly, several modern discoveries, which are now fully recognized as facts by scientific men. The guesses of Lucretius were the forerunner of verities which have been extracted from nature by following the Baconian method of obeying her with the view of learning her secrets. Generally speaking, the principles laid down by Lucretius are either true or foreshadow truths which have been brought to light by more recent research. The atomists had a clear conception of the operation of laws in nature, which the late Professor Clifford used to support the Epicurean negation of a Providence, and Professor Tyndall to show the uselessness of prayer, except for personal and individual benefits. To the atomists, the permanence and regularity of natural phenomena became the foundation of speculative inquiry, while in the hands of some scientists it is also used to subordinate religion to their particular theories. Lucretius said that light and liquid were composed of atoms; which has since been ascertained to be true. His 'hooked' (hamata) atom was a dim foreshadowing of gravity and cohesion, while his conciliation (concilium), invented to bring the atoms into contact, has some connexion with chemical affinity. There are passages in the De rerum natura which point to the transformation, conservation, and dissipation of energy as now understood. The Epicurean notion of the atoms falling eternally through space suggested to Kant the nebular hypothesis. The atomists believed that the atoms were always in motion, even in dense bodies, but they did not attempt to calculate the speed, which, under different conditions, has been ascertained by the late Professor Maxwell and others. They had also some idea, however obscure, of specific gravity, of spontaneous generation, evolution, natural selection, and survival of the fittest. Mingled with much that was absurd

and erroneous, with false analogies, and assertions about the atoms which were metaphysical and ridiculous, these and other speculations leave no doubt about the acuteness of the Greek intellect, even when groping its way amid the darkness

of the age.

While many of the speculations of the atomists were well founded, there were difficulties in their theory which they either attempted ineffectually to explain, or left entirely unnoticed. In modern times it has proved fertile in discovery in the hands of scientific men, but in several instances it has had the unfortunate effect of landing them in materialism, or even of ousting God from the control of His universe. The ancient atomists assumed that the atoms were in motion from all eternity, flying about in confusion under the influence of blind chance. At first they were supposed to be moving downward in parallel lines, but when the 'declination' took place, and one atom turned aside and struck another in the illimitable void, this originated collisions and conglomerations, which after numerous trials ended in the construction of the world. Motion was communicated by their falling downward by their own weight, Lucretius in this unconsciously assuming the world as the basis, by which to measure direction and velocity. The atoms moved of their own accord, and ultimately the world was generated.

Modern materialistic atomists are forced by their own principles to assume for their atoms eternal motion as Lucretius did. Boscovitch said that matter was made up of atoms, but in a particular sense. Each was an indivisible point, having position in space, and capable of motion. It was a geometrical centre, endowed with potential force, by which was meant that any two atoms could attract or repel each other, in proportion to the distance by which they were separated. This notion was to some extent accepted by Faraday. The idea of substance was abandoned, while the external relations by which alone the atom was capable of making known its presence, were retained. Picton, in The Mystery of Matter, putting aside the ordinary conception of atoms as indivisible particles occupying space, and taking up this theory, regards matter as 'accumulated centres of force.' He supposes

them capable of interpenetrating one another, and of thus producing a new mode of force-in other words, a new substance. He admits that force is a function of matter as much as motion is, but holds that matter in its ultimate essence is spiritual. He views it as the elementary phenomenal definition, such as consciousness is able to apprehend, of a universal