at least 100 times greater than this. A beam of light directed on equidistant mirrors, one in the direction of the stream, the other across the stream, was reflected back to the source. The ether stream should have retarded one of the beams, producing an interference fringe, but the expected result was not obtained. The ether stream was shown to be without effect on the observed velocity of light. Presuming the accuracy of the experiment, and this is not questioned, and moreover has had independent confirmation, the result is decisive for theory. It has demonstrated the constancy of the velocity of light to an observer in a moving system, and as the variation due to the ether stream must be accounted for, the only possible conclusion is that the space and time of the observer accommodate themselves to the constancy of the velocity. There is no need here to follow out the development of the theory, to describe the work of Einstein and the formulation of the general principle of relativity, which extends to gravitation and to all the laws of nature. The scientific concept of the nature of physical reality is not an absolute existence independent of mind, but a co-ordinated framework relative to the observer.

The significance of the new theory is not in the revolution it has occasioned. So far as physical science is concerned, it is no more disconcerting to treat space and time as variables than it was to treat the earth as moving when the Copernican discovery showed that the common-sense theory of a geocentric universe was untenable. The two cases are exactly analogous. The adoption of any scientific basis of reality is to some extent arbitrary; what drives us to it is not obstinate fact but convenience. The principle of relativity is adopted because it is more convenient. It is true indeed that the new principle extends the range of mathematics, also it reconciles some puzzling discrepancies between astronomical calculation and fact which were not due to error. The true significance of the theory is only seen, however, when the whole historical evolution is taken into account. It is the recognition that it is impossible to co-ordinate the physical universe without taking into

account the observer's standpoint. It marks the introduction into science, and full recognition of, a monadic principle. The observer in a system in relative translation in regard to other systems measures his universe from his own standpoint by three dimensions of space and the one dimension of time. These dimensions are not constant; they vary with the acceleration and direction of the translation of the system, and by their variation velocities are kept constant. This is a new world-view.

The universe consists of events, and these events are co-ordinated by the observer so that a constant ratio between space and time is maintained. Space and time vary, therefore, with the system of reference, and ultimately every observer is the unique centre of his own system of reference. There is therefore no objective scale by reference to which magnitudes can be assigned an absolute value. Great and small are relative terms. We all recognize the constancy of velocity when we compare the range of activity of a human being with that of other living creatures. For as an insect's world is smaller than ours and a bird's world more extended, we must imagine each creature to co-ordinate its world on a scale of its own and not on ours. But the world-view which science now presents to us enables us to apply this principle of the constancy of velocity on an infinite scale. Physical science, in fact, presents to our view a universe which is as amazing in its limitations as it is infinite in its vista. At one of its limits, above us, as we say, is the stellar system, and at the other limit, below us, as we say, is the atomic system. These bound for us the scientific horizon, but they are not indefinite limits indicating an obscurity into which the mind can penetrate no further. They are clear systematic, inclusive concepts which give to our universe the character of an objective, organic selfrepeating design. The planet on which our life has evolved appears to our imagination as the electron of a vastly magnified atom, and the atom is a solar system shrunk to infinitesimal proportions. The principle of relativity shows us that this great and little are not absolute magnitudes.

The infinitely great becomes infinitely little when the observer changes his system of reference. Shrunk to the proportions of the atom, the electron of the physicist becomes for the observer a planet revolving in its orbit round a sun, and we have only to imagine a being of Olympian proportions and the necessary range of activity to see earth and sun and stars dwindle to atoms. Whatever change the new system may introduce in the quality of experience the proportions will remain the same. Such is the significance of the constancy of velocity in the principle of relativity.

This brief outline of some of the distinct stages in the evolution of the scientific concept of physical reality is intended to emphasize the impossibility of separating scientific and philosophical development. At one time the fashionable theory was that science had superseded philosophy. It was declared to mark a new era, a definite progress in human reason and a new stage in freedom from mental bondage. The old mythological and theological stage had been replaced by a metaphysical stage, and now in modern inductive science, it was said, a new positive stage had come to supersede the vague and unsatisfactory speculations of philosophy. A mere glance at the historical connexions shows how shallow this judgment was. To-day it is impossible to ignore the claims of philosophy, but it is usual to accord it, often grudgingly, a place of subsidiary importance, dealing with subjects altogether distinct from the sciences, and not possessing like them a sure basis in physical reality. But history shows us that the supposed clear lines of demarcation are arbitrary and false. Philosophy depends on the world-view. Modern science and modern philosophy arose together when the heliocentric discovery altered the world-view. At every stage the speculative or large view of the philosopher has acted and reacted on the analytical and experimental research of the scientific investigator. For a long time indeed the methods seemed to diverge, but to-day we are witnessing a remarkable approximation. The approximation is due to the recognition of the monadic principle.

CHAPTER IV

THE CONCEPT OF NATURE IN PHILOSOPHY

Whose is this image and superscription ?-ST. Matthew.

It is as certain as any scientific truth can be that this earth existed ages before there was any conscious life upon it, and that it will continue to exist ages after its condition shall have rendered life impossible in any form of which we have experience. It is true that to present this existence to the imagination we are dependent on sense-imagery, we can only represent it as potential consciousness, but this does not affect our confidence that something has existed, does exist, and will exist, independently of whether any cognitive being has existed, does exist, or will exist to know it. The classical arguments of the idealists leave us cold. We may hold with Spinoza that extension is a mode of the infinite substance, God; we may believe with Fechner that there is a world-soul expressing itself in the physical universe; we may find satisfaction in the idea of a spiritual absolute, an ultimate harmony, in which the contradictions and antinomies of temporal existence are reconciled; but the main fact of our conscious being seems to be our relation to an externality which, whether or not it is dependent on spirit, is itself non-spiritual.

The aspect of nature as indifferent and hostile to spirit is as prominent a feature of the old world-view as it is of the new, and it finds abundant expression in ancient literature, but the new world-view has given it new embodiment. The modern scientific concept of physical reality has made practically impossible the direct and easy solution

offered by the old world-view in the theory of special creation. We may still believe that the words " In the beginning God created the heavens, and the earth" are philosophically true, but we can no longer refer them to a definite temporal event, however far back in time we remove it. We can only smile at the serious mood in which the seventeenthcentury philosophers disputed concerning the nature of the creative act. "From the beginning," wrote Leibniz, "God has made each of these two substances (the soul and the body) of such a nature that merely by following its own peculiar laws, received with its being, it nevertheless accords with the other, just as if there were a mutual influence, or as if God always put his hand thereto in addition to his general co-operation." It is quite impossible for us even to conceive the creative act which should bring the world into being, and we no longer seek the answer to our problem by reasoning about its nature or trying to fix its date. And this means that for us the concept of God has changed with the world-view, and as completely. It does not mean that our philosophy is atheistic, for the old atheism is as impossible as the old theism; neither touches the fringe of the great problem which the new world-view has disclosed. With the geocentric universe has gone the idea of the artificer and the analogy between the skilful contriver of a perfect machine and the architect of the universe, but the essential problem survives in a new form. Let us look at that problem.

One of the most magnificent expressions of the aspect of nature as a sublime and awful force, indifferent to man, however completely subject to higher spiritual powers, is the Book of Job. It begins with the drama in heaven where Satan appears among the Sons of God with the sequel of the great fourfold catastrophe which leaves Job desolate. We are told that "Job arose, and rent his mantle, and shaved his head, and fell down upon the ground and worshipped; and he said, Naked came I out of my mother's womb, and naked shall I return thither the Lord gave and the Lord hath taken away; blessed be the name of the Lord." In these words we seem to have the agonized expression