Note 1355 — Chapter XVII
Reading edition
It is certain that Vieta perfectly knew the relation of algebra to magnitude as well as number, as the first pages of his In Artem Analyticam Isagoge fully show. But it is equally certain that Tartaglia and Cardan, and much older writers, Oriental as well as European, knew the same; it was by help of geometry, which Cardan calls via regia, that the former made his great discovery of the solution of cubic equations. Cossali, ii. 147. Cardan, Ars Magna, ch. xi.