Leeuwenhoek improves the microscope by polishing and grinding the lenses to the ability to see single-celled organisms.
Leeuwenhoek's microscope was extremely simple and represented a plate with a lens in the center. The observer had to look through the lens at the sample, fixed on the other side, through which the bright light from the window or candle passed.
Leeuwenhoek is considered the founder of the study of microscopy and played an important role in development of cell theory.
Despite the simple construction, the quality of its lenses in the microscope made it possible, for the first time in history, to see many microscopic animals, bacteria, and complex details of common objects.