the thought of the age. Everyone is a victim, but no one is to be blamed.

I know of no better examples than the two plays of Tchekhof, which have lately been translated by Mr George Calderon-'The Seagull' and 'The Cherry Orchard.' There is assuredly no hero and no villain. We do not know whether we are dealing with a tragedy or a comedy; and, in the case of 'The Cherry Orchard,' at all events, the drama ends because the principal situation studied has come to a conclusion, not because the dramatist has formed an idea of a dénouement. In 'The Cherry Orchard' you have the contrast between a vulgar successful man and the nobility. But you must not think that the vulgar successful man is intended to be the villain of the piece. No, he is a very good-humoured creature, full of kindness, and perhaps representing some of the lineaments of Tchekhof himself. So, too, in 'The Seagull,' the successful author who does so much damage to young people, who ruins, practically, the lives both of a young girl and the young man who is her lover, is in reality a capital fellow, fond of fishing, once more possessing some of the lineaments of Tchekhof himself. If one thinks over the matter, there is no better way of trying to decide the directions in which drama is evolving than to study modern drama as it meets us in unfamiliar forms in other nations. Tchekhof is an admirable example to choose, because Tchekhof is full of a delicate artistry, and because he consciously set himself to write, not the conventional dramas which were likely to win immediate success with his public, but those more intricate studies of human life and human nature, which reveal the tragi-comedy of the world. And it is towards this illustration of the tragi-comedy of life and character in the world that all serious modern drama in England and elsewhere is slowly feeling its way. What modern drama needs is not so much a brand-new technique that is impossible-as an adaptation or modification of the old technique to suit the prevalent conceptions of the age. W. L. COURTNEY.

Art. 6. THE INDIVIDUAL ATOM.

1. Griechische Denker. Eine Geschichte der Antiken Philosophie. By Theodor Gomperz. Leipzig, 1896–1912. 2. Histoire de la Philosophie Atomistique. By Léopold

Mabilleau. Paris: Alcan, 1895.

3. The Study of Chemical Composition: Its Method and Historical Development. By Ida Freund. Cambridge: University Press, 1904.

4. Radio-active Substances and their Radiations. By E. Rutherford. Cambridge: University Press, 1913.

5. The Conduction of Electricity through Gases. By Sir J. J. Thomson. Second edition. Cambridge: University Press, 1906.

6. An Electrical Method of Counting the Number of aParticles from Radio-active Substances. By E. Rutherford and H. Geiger. Proceedings of the Royal Society, A. 81, p. 141. June 1908.

7. On an Expansion Apparatus for making Visible the Tracks of Ionising Particles in Gases and some Results obtained by its Use. By C. T. R. Wilson. Proceedings of the Royal Society, A. 87, p. 277. June 1912.

THE theory of atoms, as an attempt to explain the ultimate structure of matter, has occupied an important place in the organised pursuit of natural knowledge; but from the days of Democritus to those of Lord Kelvin speculation on the atomic theory has rested on the assumption that vast numbers of atoms or molecules were needed to produce results appreciable by the senses; and, till recent years, the demonstration of the separate effects of a single atom was regarded as beyond human power. Thus molecular science could be treated only by statistical methods, in which the properties of the individual had to be inferred from a knowledge of the properties of immense crowds.

Philosophers and men of science are not agreed on the question whether or no the pictures of the outer world given us directly by our senses or indirectly by scientific analysis correspond to a reality in the 'things-inthemselves'-whether, indeed, we can ever apprehend the 'thing-in-itself' by means of the perceptions which alone can reach our minds through the senses. But even many

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of those who held a realist creed and believed in the existence of something-unknown in form perhaps, but still something-corresponding to our mental pictures in general, had doubts about the reality' of the individual atom. While they accepted the atoms as convenient conceptual entities which led to results in accordance with experience when from hypothetical atomic properties those of matter in bulk were deduced, they felt no confidence that atoms stood for more than a system of symbols which had hitherto led to consistent results on integration.

But now, by the genius of Prof. Rutherford on the one hand and of Mr C. T. R. Wilson on the other, we have two distinct methods of making visible the effect of one single atom of matter shot out of that amazing form of automatic gun, a speck of a salt of radium. Moreover, it has been shown that a third older method, due to Sir William Crookes, gives yet another means of detecting an atomic effect. In a very real sense these results form a consummation of the atomic theory. Rising from a correct, though vague and unverified guess of a Greek philosopher, whose chief merit lay in the perception that matter must be either continuous and homogeneous or discontinuous and atomic, through the useful and necessary working hypothesis of Dalton's chemistry based on definite experimental evidence, the atomic theory has stood the final test; and the atom has become as real as any other conception which corresponds to something that can affect our senses and be made appreciable to them.

At this stage, then, it seems appropriate to give a short summary of the history of the theory of atoms, and to trace the varying importance that has been allotted to it throughout the ages. For the atomic theory has had many uses. It has been the subject matter of philosophical dispute; it has served as a weapon in religious controversy; it has become an essential part in a theory of chemical combination applicable to industrial processes; and it is often put forward as a final statement of the essence of the underlying phenomena on which men have built up an explanation of the whole world of material manifestation. No one of these aspects is more fundamental than the other; and the exponent of any parti

cular phase has much to learn by keeping in mind the many-sided nature of the hypothesis.

We appear to owe the conception of an atom as well as the word by which it is expressed to the philosophers of Greece-the first men of science and conscious students of Nature known to history. The earliest Greek atomist seems to have been Leucippus, of whom little trace save tradition survives. His disciple Democritus is a less shadowy figure. Democritus was born at Abdera about 460 B.C., and there, after many wanderings, he returned to live and die. Our knowledge of his philosophy is derived chiefly from Aristotle's account of it-an unfavourable one-and from the poem of the Roman Lucretius, where, interwoven with the additions and modifications due to Epicurus, it is described in detail and given its philosophic import.

It is unfair and misleading to compare the atomic philosophy of the Greeks with the definite chemical theory developed by Dalton and Avogadro in the early years of the 19th century out of the physical speculations of Boyle and Newton. The modern theory arose naturally as an exact and limited working hypothesis, framed to explain or co-ordinate a number of facts obtained by the experimental method. The ground had been prepared for it by countless patient investigators; and at once it was seen to bring order and intelligibility into a host of disconnected phenomena. It was a scientific hypothesis, and had all the sharply-cut though narrowly circumscribed field of usefulness characteristic of its nature. It had little immediate philosophic bearing even of an indirect kind, and we are not aware that the sleepless vigilance of theologians detected in it any attack on religion. But the whole object and meaning of the theory of Leucippus and Democritus and Epicurus at the time when it was put forth was primarily and ultimately philosophic and religious. It was the first great attempt at a rationalist explanation of the Universe, the first recorded effort to trace mechanism instead of caprice in the workings of Nature, both in the physical and in the biological realm. It was an attack on the received dogmas of religion; an onslaught at once on the Homeric gods of Olympus, and on those formless, distressful

deities in the background, which had been developed by the southern aboriginal race out of the more primitive cults of magic and tabu before the invasion of the conquering northern Achaeans and Dorians had introduced their anthropomorphic and friendly gods born and bred in regions beyond the mountains.

The attempt to explain Nature in terms of known mechanical principles, with the object of doing away with the need of direct divine interposition, is, then, the task of the Greek atomists. Of course, from the philosophic point of view, ancient or modern, there remains the ultimate insufficiency of all physical explanation. Such explanation is but the expression of one unknown in terms of another, which seems understood merely because it is so familiar that the mystery is no longer consciously apprehended. But then, as always, the less clear-sighted champions of orthodoxy took up positions which were unnecessarily exposed to attack, and denounced Democritus and Epicurus, in a way that must have assured those philosophers that the success of their endeavours to undermine the traditional beliefs was only a matter of time and opportunity. But here and now we are concerned less with the ultimate religious and philosophic import of the atomic theory than with the details of the earliest speculation about the structure of matter. If matter be infinitely subdivisible, argued the atomists, subdivisible into an unending series of smaller and yet smaller particles, all of the same nature, and with the same properties as matter in bulk, no explanation of the immediate properties of the various kinds of matter as revealed by our senses is possible; we have to accept these properties as fundamental and ultimate incomprehensibles. But if, in a process of subdivision, we come at one point to structures which can be subdivided no further-individual structures the properties of which are not those of matter in bulk-we drive back the incomprehensible at least one step. We may hope to explain the immediately perceptible properties of matter in terms of the interactions of those ultimate atoms.

Moreover, since movement is possible, since division can take place, there must exist empty space or void. If all nature were full, nothing could move or separate, because nothing could give way to make room for any