248x silver

In 2014, this microscope was discovered in a collection of doll house accessories purchased in England by Dutch collector Bert Degenaar. The microscope was authenticated in 2015 and was on display at the Boerhaave until September 2015, after which it traveled to Utrecht, Oxford and Berkeley. It then returned to Mr. Degenaar's Planetarium Zuylenburgh in Oud-Zuilen, just north of Utrecht.

The silver hallmarks visible on the eye-side plate help prove its authentencity. The provenance is unknown. According to Tiemen Cocquyt's "De identificatie van een zilveren microscoopje van Antoni van Leeuwenhoek", it is engraved (in the 19th century?) with the letters JW and stamped with genuine Dutch silver hallmarks which indicates that this microscope was traded between 1807 and 1810, and again between 1814 and 1831. These marks were applied well before replicas of scientific instruments became common or popular.

Therefore this instrument existed many decades before the English antiquarian John Mayall manufactured copies, starting in the late 1880s. As noted by Van Zuylen, "On the microscopes", from 1886 onwards, the English antiquarian John Mayall, secretary of the Royal Microscopical Society, made several copies modelled after the Utrecht microscope which was exhibited that year in London.

The Boerhaave's recent measurements by Tiemen Cocquyt follow the method of the late Jan van Zuylen who measured all other known Leeuwenhoek microscopes. The report note that this 248x silver microscope has an affinity with the 266x Utrecht microscope in terms of refractive index, magnification, and the presence in the glass of miniscule air bubbles.

The page on "Constructing the Microscopes" on the right sidebar menu discusses the features of this microscope in more detail.