Christiaan Huygens received letter from Gutschoven about how to grind small lenses

In the summer of 1663, Christiaan Huygens received a letter from René François de Sluse (1622-1685), a mathematician interested in optics. He was from the Spanish Netherlands (now Belgium) and had graduated from the university at Leuven, whose faculty would award Leeuwenhoek with a medal in 1716.

Sluze and Huygens had been corresponding for several years about topics like tangents and volumes under curves. Their correspondence would continue for several more years about topics like Huygen's pendulum clock.

With this August 1663 letter, Sluze enclosed a short piece in Latin with three illustrations (right; click to enlarge). It was from Gerard van Gutschoven (1615-1668), a mathematician at the university at Leuven.

In the early 1630's (when Leeuwenhoek was a child), Gutschoven was a pupil and assistant of Descartes in the Dutch Republic. In 1635, he returned to his home town of Leuven, where he became professor of mathematics in 1646 as successor to Sturmius. After the death of his wife Anna Leroy (1652), Gutschoven entered the monastery, and in 1659 he became professor of anatomy, surgery and botany.

The letters of Huygens includes correspondence with Gutschoven from 1652-56 about mathematical topics.

The undated enclosure in Sluze's August 1663 letter explains how to grind small lenses. Until then, Huygens had been more interested in and very successful at grinding lenses for telescopes. By the early 1660's, however, he became interested in small magnifying lenses, perhaps influenced by his acquaintances Spinoza and Johannes Hudde.

When Leeuwenhoek became known ten years later for his work with tiny lenses, Huygens would not have been surprised. It is not so surpising then that a half century after that, in 1716, the pro-Cartesian faculty at Leuven honored the pro-Cartesian Leeuwenhoek.