Letters on the English author of "Novum Organum" and father of experimental philosophy. Letter 13 is about John Locke and his theories on the immortality of the soul. Letter 14 compares British philosopher Isaac Newton to French philosopher René Descartes. Upon his death in 1727, Newton was compared to Descartes in a eulogy performed by French philosopher Fontenelle. While the British did not appreciate this comparison, Voltaire argues that Descartes, too, was a great philosopher and mathematician. Letter 15 focuses on Newton's law of universal gravitation. Letter 16 talks about Newton's work with optics. Letter 17 discusses Newton's work with geometry and his theories
Philosophy of the Unconscious of the scales, and his 'World-process' in the other. There are some who believe they weigh equally; for in each scale there is an evil word—and a good joke." Hartmann's work has been seen as preparing the way for Freud's later theory of the unconscious. Freud consulted "Philosophy of the Unconscious" while writing "The Interpretation of Dreams" (1899), in which he called Hartmann the firmest opponent of the theory that dreams are wish fulfillments. The philosopher Hans Vaihinger was influenced by "Philosophy of the Unconscious", relating in his "The Philosophy of 'As if'" (1911) how it led him to Schopenhauer.