Loupes and multiple lenses

Loupes

If the number of aquatic-microscope lenses is a mystery, so is the number of loupes in Leeuwenhoek's legacy, 88. They all contained unique lenses and they had the advantage of being portable. Leeuwenhoek could carry several into the woods or polders to make preliminary inspections. Remember that as a cloth merchant, he used a much lower-powered loupe to count threads. They had a cup on the eye-side, presumably to reduce light.

The images right and left come from his letter of January 12, 1689, to the Royal Society. In it, he discussed how he made and used his eel and fish viewers. The plate included these two figures. They are also shown on van Seters' figure showing all the types and metal variants. The image below right from the title page of Vijfde Vervolg der Brieven in 1696 shows an angel bringing a loupe to her eye.

Multiple lenses

Leeuwenhoek also made devices that had more than two or three lens, a specimen pin behind each. See images below.

A two-lens version was sketched in detail for Uffenbach's third volume of travel writing. Two other sketches are in van Seters' article. Two images show a three-lens version. In Verkolje's portrait from 1685?, Leeuwenhoek is holding one in his left hand. On the title-print of the 1747 auction catalogue, a cherub is peering through one.

While these microscopes have multiple lenses and multiple specimen pins, they have only one positioning screw, one braking screw, and one mount or stage. Thus, getting one specimen in focus probably puts the others out of focus. For comparison purposes, two single lens microscopes held by clamps side by side probably worked as well. Perhaps this is why Leeuwenhoek made only five of these multiple-lens microscopes.