17th-century microscope. Historical engraving of an early microscope made by the Dutch scientist Anton van Leeuwenhoek (1632-1723). Leeuwenhoek's microscopes used a single lens, mounted in the flat sheet at upper left, which he ground to near perfection himself. The subjects were contained in the test tube in the middle of the device. Magnifications of up to x300 could be achieved: enough for Leeuwenhoek to become the first to see protozoa and bacteria (which he called little animalcules") in water. He also made detailed studies of capillary networks and insect life- cycles. His work was held in high esteem, and he was made a Fellow of the Royal Society of England."