branch of study: optics
inventor: Antoni van Leeuwenhoek, around 1700
Antoni van Leeuwenhoek (1632 – 1723) was a Dutch natural philosopher and to this day very much known for the development of several hundred microscopes. He produced the lenses for the microscopes himself and even developed a particular technique. In the early 18th century, glass was generally of a poor quality and so he only used tiny self-made lenses which provided an enormous magnification.
Among his scientific findings was proof that flea are indeed born after a metamorphosis cycle and did not form spontaneously from sand, dust and dirt.
Lawrence, John (2011): A Brief History of the Microscope, in: Bulletin of the Scientific Insturment Society (SIS), No. 110, S. 35ff.
Replica Leeuwenhoek Microscope at Museum Boerhaave, Leiden, NL. (Link)