The Theory of Parallels
Lobachevski was the first to publish non-Euclidean geometry. Originally titled: Geometrical Researches on The Theory of Parallels. This is an unabridged printing, to include all figures, from the translation by Halsted.
Jung contra Freud: The 1912 New York Lectures on the Theory of Psychoanalysis (Bollingen Series (General))
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Euclid's Elements
The Principia : Mathematical Principles of Natural Philosophy
Lucretius: On the Nature of Things (Loeb Classical Library No. 181) (Bks. 1-6)
Discourse on Method (Hackett Classics)