The drawing below is taken from S. Bradbury (1967), The Evolution of the Microscope, showing a similar microscope as it appears in Johannes Zahn (1702) book Oculus Artificialis Teledioptricus in comparison with the microscope type seen here.

Fruitwood "flea glass" simple microscope, 1680-1750

 

This is an early version of a type of simple microscope made of fruitwood. It has a single, biconvex lens mounted in an aperture in the top turned wood piece. The lens is maintained in position with a brass circlip and the instrument is contained within a cylindrical pasteboard etui coated by marbled paper. These microscopes appear in several forms. They were apparently produced by “toymakers” in Italy and the German lands to satisfy the curiosity of the common people in natural science. This type of handheld microscope was popular during the late 17th and probably well into the 18th century. They were made of wood, horn, and bone. 

The magnification lens is facing a brass sprung pin to which a flower or an insect could be speared for inspection (thus the term "flea glass", an English translation of the Latin name vitrum pulicarium). Focusing was achieved by moving the sprung pin backward or towards the lens. 
 

Johann Franz Griendel von Ach und Wankhausen in Micrographia nova Battle Between Flea and Louse 1687

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