"Prof. B. J. Delbœuf and Prof. H. Poincaré have expressed their conceptions as to the nature of the bases of mathematics, in articles contributed to The Monist. The latter treats the subject from a purely mathematical standpoint, while Dr. Ernst Mach in his little book Space and Geometry, in the chapter "On Physiological, as Distinguished from Geometrical, Space" attacks the problem in a very original manner and takes into consideration mainly the natural growth of space conception. His exposition might be called "the physics of geometry.""