The recent remarkable developments of physical theories, especially those concerned with relativity and quanta Of energy, cannot fail to have far-reach ing in?uences on philosophical thought. Physicists, as a rule, are too much occupied with their special field to give much attention to matters of more general philosophical interest, and few philosophers possess the knowledge of science required for dis cussing and criticizing fruitfully the work of the physicist. Professor Rougier's very wide reading in mathematical and experimental Physics has en abled him to present and interpret the new ad vances in Physics in a way which should prove of great interest to both philosopher and physicist. This book seems to mark a measurable advance toward a con?uence of the broad streams of philo sophical and scientific enquiry.