In 1610, Johann Kepler developed the basic modern arrangement for the compound microscope, which Leeuwenhoek would put into practice, at the end of the century.
In 1658 Jan Swammerdam saw red blood cells under a microscope, described red corpuscles, lymphatic valves, and changes in the shape of muscles in contraction.
1665 Robert Hooke published his Micrographia, making microscopy popular, identifies cells, and also proposed that artificial silk may be made by extruding gum.
In 1674 Anton van Leeuwenhoek invented the compound microscope, and then went on to discover and describe various Protozoa, bacteria, and rotifers.
In 1722, Daniel Defoe made a casual reference to theories that plague was caused by microbes, too small to be seen without the aid of a lens or microscope.
In 1830, Joseph Jackson Lister, the father of the more famous Joseph Lister, showed how compound lenses can correct for chromatic and spherical aberration.
Medical practitioners may not need a microscope today, but microscopes were essential to medical researchers in the past as they sought the causes of diseases.
Only a microscope would let researchers to examine the shape of bacteria, and to see which stains were absorbed by the cell wall of a suspicious bacterium.
Only a microscope would let researchers to examine fine detail like a number of hairs on a mosquito's leg, and so identify a species that was a disease vector.
Microscopes were also important to geologists, because it is easy to identify minerals in thin sections of rock with polarized light, filters, and a microscope.
There is a limit to how much a microscope can magnify, which depends on the wavelength of the light used, and the size of the object being looked at.
Because electrons behave in some ways like light, it is possible to make a microscope which uses electron beams instead of light to see very fine detail.