Perspective in Leibniz's invention of \textit{characteristica geometrica}: the problem of Desargues' influence (Q391354)

From 1677 on and throughout his life Leibniz spent considerable effort on the design of a new symbolic calculus, which he called alternatively \textit{characteristica geometrica}, \textit{geometria situs} and \textit{analysis situs}. Its aim was to encode geometric arguments and thereby make the use of figures superfluous. Furthermore, in contrast to Cartesian analysis, it was designed to be coordinate-free. Instead of magnitude, its basic notion was the relative position of geometrical objects in space, the \textit{situs}.NEWLINENEWLINEDuring his stay in Paris (1672--1676), Leibniz got to know Desargues' work, but it is difficult to determine to what extent. Since he mentioned Desargues quite often without acknowledging any direct influence, the question studied in the present paper, how far his project of a \textit{characteristica geometrica} was inspired by Desargues, is natural. One difference is obvious (p. 376): The fundament of Leibniz's geometrical calculus is Euclidean plane geometry and not projective geometry.NEWLINENEWLINEAfter reviewing ideas of Desargues which may have interested and influenced Leibniz and confronting them with key concepts of Leibniz's \textit{geometria situs}, the author concludes: ``[I]t appears that what is common is what distinguishes these two kinds of geometrical methods: the role of quantity, the place of figures and the imagination, the relation between similarity and congruence, the use of the identification of parallel and secant lines, and the conception of space through perceptive considerations.'' (p. 382). In the end, the author points to the influence of other sources, in particular Pascal (p. 382 f.).