tion of the material world. This problem is considered from different angles in a number of addresses m t is volume, including a discussion on the laws of chance and the principle of indeterminism, and the meaning of a law of Nature. The last chapter, containing the address given by him in Stockholm on the occasion of the award of a Nobel Prize last year, is of much interest, for it brings out in a striking way the rela¬ tions between the new and older ideas, and the pos¬ sible reconciliation between the different aspects of Nature involved in the particle and wave conceptions of matter. On these fundamental questions involving the meaning and scope of the law of causality there is room for much difference of opinion but many in this country, whether they agree with the author or not, will read these charming and simply-written essays with much pleasure and interest.