This is P.D. Ouspensky's Tertium Organum, which he believed was the third major philosophical synthesis, the previous being those of Aristotle and Bacon. Ouspensky (1878-1947) was a mystic who traveled widely in Europe and the East looking for esoteric knowledge. He later studied with G.I. Gurdjieff. In this book, he uses the concept of the fourth dimension as an extended metaphor for the esoteric nature of reality. Einstein and other physicists had at that time validated the study of higher dimensions, and Ouspensky was fixated on this idea. One can only wonder at what he would think of string theory, parallel universes, and the holographic universe hypothesis (the latter of which he prefigures in this book).