Maxwell’s remark is now seen to have been prophetic. The extraordinarily profound and far-reaching philosophical implications of the theory of relativity have hardly yet begun to be investigated, but we have already a general sense of their direction. Hermann Weyl’s _Raum, Zeit, Materie_, for instance, the most thorough mathematical exposition of the whole theory which has yet appeared, hints not obscurely at the philosophical bearing of the new investigations. Now that, by Weyl’s own work, Maxwell’s electromagnetic equations are included by the theory, it seems to be scientifically complete. It presents us with a picture of the universe which is wholly unlike the picture of the early physics. In particular, an altogether different rôle is assigned to the human mind. So far as the exterior universe and the laws of nature are concerned, we see that the primary entity is the mind itself. It is the mind which has created, not only space and time, but the matter it has put within that framework. The mind has not created the universe out of nothing, it is true. But it is almost impossible to say anything intelligible in the old sense about the fundamental entities to which Einstein’s theory leads us. Professor Eddington suggests that they may be “the very stuff of our consciousness,” a somewhat mystical remark which nevertheless shows the trend of the new speculations. And, as a striking confirmation of Maxwell’s view of the possible development of physical science, we may quote one of the last sentences of Weyl’s profound discussion: “It must be emphatically stated that the present state of physics lends no support whatever to the belief that there is a causality of physical nature which is founded on rigorously exact laws.” Unfortunately not all men are mathematicians. The great and wonderful vista now opened up by Science--greater and more significant, we believe, than has existed at any previous time in the history of thought--is at present a consequence of highly abstruse investigations. The sheer technical difficulty of these inquiries will long hinder them from exerting their due influence on philosophy and, through philosophy, on the whole of the intellectual life of the age. But the new conceptions exist, and they derive their unshakable strength from the fact that they are the result of the severest Science. And surely no one can fail to see that they promise not only fascinating regions for thought, but a new liberation of the human spirit. Mystery, but more wonderful and full of promise than ever, has been restored to the universe. MATHEMATICS AND MUSIC