Called "an illiterate, but ingenious man"

Date: 
August 25, 1679

Peter Pels wrote from The Hague on 25 August 1679 (my translation and emphasis)

Den inventeur tot Delf is den ordinaris camerbewaarder van het stadhuijs aldaer. Hij is een ongeletterd, maer inventif man. Hij wil door sijne glaasjes wel laeten sien, maer geene wegh vereeren, noch verkoopen. Aen Duc de Jork selfs heeft hij het geweigert; aen de Vorst van Vrieslant, en aen meer andere.

Daer sijn ook wel andere soorten van microscopia, maer dien van Delft schijnt de speculatifste te weesen. Behalve de ordinaris heeft hij extraordinaire inventien, die extraordinaris vergrooten, doch noijt laet sien. Hij heeft veel kijkers, die hem altemets wat wegh ficken, ’t welk hem moeijlijk maeckt.

The inventor in Delft is the ordinary keeper of the main chamber at the city hall. He is an illiterate, but ingenious man. He allows one to view through his glasses, but he does not want to give or sell them. To the Duke of York [the later King James II of England] even he has refused it; as to the Frisian Stadtholder [Hendrik Casimir II of Nassau-Dietz] and others.

There are other kinds of microscopes, but those of Delft seem to be the most revealing. Except the usual [microscopes], he has exceptional inventions, which magnify extraordinarily, but which he never shows. He has many viewers, who sometimes offend him, which makes him [a] difficult [man].

Source: Observatoire de Paris, Hevelius correspondence, vol. 14, no. 2103-2104.

Quoted in: "Antony van Leeuwenhoek’s microscopes and other scientific instruments:
new information from the Delft archives"