Available in PDF, epub, and Kindle ebook. This book has 367 pages in the PDF version, and was originally published in 1922.
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. Originally issued in Russian in 1912, this is the second, revised edition. It was translated into English and published in 1922. In this book, Ouspensky uses the concept of the fourth dimension as an extended metaphor for the esoteric nature of reality.
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