Early microscope design, historical image. Diagram of an early microscope made by the English dyer and amateur astronomer Stephen Gray (1666-1736). This device was inspired by a similar one designed by the Dutch scientist Anton van Leeuwenhoek (1632-1723). It has a single lens mounted in a flat sheet of metal, which allows magnifications of up to x200. In the 1670s, Leeuwenhoek used a microscope similar to this in order to observe and describe single-celled animals (protozoa and bacteria), which he named 'animalcules', for the first time in history. Image from 'La Conquete Du Monde Invisible' by Giuseppe Penso (1981).