Through an in-depth analysis of the notes that Leibniz made while reading Pascal’s manuscript treatise on conic sections, we aim to show the real extension of what he called “hexagrammum mysticum”, and to highlight the main results he achieved in this field, as well as proposing plausible proofs of them according to the methods he seems to have developed.

No século XVII, vemos a emergência de uma nova abordagem geométrica às seções cônicas. Desenvolvida inicialmente por Girard Desargues e por Blaise Pascal, tal geometria é herdeira do método de representação pela perspectiva linear a aponta na direção da geometria projetiva do século XIX. Estudos recentes de J. Echeverría e de V. Debuiche iniciaram a discussão da recepção de tais trabalhos por Leibniz, assim como a relação deles com os trabalhos do próprio Leibniz em perspectiva e com a Geometria situs. (...) Este artigo percorre algumas questões associadas a estes domínios, assim como a importância do paradigma da perspectiva para a filosofia de Leibniz. (shrink)

This is an attempt to explain Kepler’s invention of the first “non-cone-based” system of conics, and to put it into a historical perspective.

In this paper, we try to understand what considerations and possible sources of inspiration Desargues used to formulate his concepts of involution and transversal, and to state the related theorems that are at the basis of his Brouillon project. To this end, we trace some clues which are found scattered throughout his works, we connect them together in the light of his experience and knowledge in the field of perspective, and we investigate what were his motivations within Mersenne’s academy. As (...) a result of our research, we can safely say that were his great geometrical insight and his projective vision of space which, guided by some classical theorems, led him to these completely new concepts in the panorama of the geometry of that time that were destined to remain misunderstood for about two centuries. (shrink)

In this paper I will examine what Blaise Pascal means by “infinite distance”, both in his works on projective geometry and in the apologetics of the Pensées’s. I suggest that there is a difference of meaning in these two uses of “infinite distance”, and that the Pensées’s use of it also bears relations to the mathematical concept of heterogeneity. I also consider the relation between the finite and the infinite and the acceptance of paradoxical relations by Pascal.