Porisms

…his commentary on Euclid’s lost Porisms in Book 7 was a subject of living interest for Jean-Victor Poncelet (1788–1867) and Michel Chasles (1793–1880) in their development of projective geometry.

According to Pappus, the Porisms (“Corollaries”), in three books, contained 171 propositions. Michel Chasles (1793–1880) conjectured that the work contained propositions belonging to the modern theory of transversals and to projective geometry. Like the fate of earlier “Elements,” Euclid’s Conics, in four books, was supplanted by a more thorough…