Nicolaas Hartsoeker

Nicolaas Hartsoeker, who lived from 1656 to 1725, was a Dutch mathematician and physicist who invented the screw-barrel simple microscope around 1694. The son of a Remonstrant minister, he grew up in Rotterdam, made his living as a lens maker and was instructed in optics by Antonie van Leeuwenhoek. In 1674 he and a fellow student, assisted by Leeuwenhoek, were the first to observe semen, which later led to a priority dispute over the discovery of spermatozoids. In 1678 he accompanied Christiaan Huygens to Paris, and from 1684 to 1698 he lived there making instruments for the Paris observatory and the academy and devising ways of aiming very large aerial telescopes. His 1694 Essay on dioptrics set out his spermist theory of conception, in which he postulated tiny men called homunculi in sperm, though he never claimed to have seen them.