Texts in Latin, marginalia in italics. With a large number of, among other things, also full-page woodcuts: educational diagrams, devices and their use, demonstration of optical and meteorological phenomena. Furthermore, tables, initials and vignettes, all done in richly printed prints of the leading period office. Wide edges of sheets, excellent condition of preservation of the book block. Contains: 1) Principia philosophiae. 19 sheets, 222 pages, 1 unprinted sheet, 2) Specimina philosophiae: seu dissertatio de methodo ... dioptrice et meteora. 8 sheets, 248 pages. René Descartes (1596-1650) was a French philosopher, mathematician and physicist, innovator of scientific thought, creator of a modern rationalistically analytical, skeptical and critical approach to the study of natural phenomena and philosophy, the Cartesian system. The sentence "Cogito, ergo sum" attributed to him (I think, therefore I am) was probably created during the translation of his French text into Latin.