Just when scientists thought they explored the whole world, numerous more arrived. During the Renaissance, the light microscope was developed which was the first instrument that enabled the human eye to observe enlarged images of infinitesimal objects. This incredible invention brought fascinating detail of the tiny worlds invisible to the naked eye. About 1950, Dutch spectacle makers, Zaccharias Janssen and his son Hans, were experimenting in the Netherlands with several lenses in a tube. They discovered that the nearby objects appeared greatly enlarged.
Years later Anton van Leeuwenhoek, of Holland the father of microscopy, taught himself methods for grinding and 
polishing tiny lenses with great curvature as an apprentice at a dry goods store where magnifying glasses helped count threads in cloth. These eventually led to the building of his light microscopes and famous biological discoveries which made him well known. This man was the first to observe and describe bacteria, yeast plants, drops of water, and blood circulation. Anton’s discoveries and studies ended up being reported as findings in over a hundred letters to the Royal Society of England and the French Academy.
In the 1930’s, the first electron microscope was introduced by co-inventor Germans Max Knoll and Ernst Ruska. They were awarded half of the Nobel Prize for Physics in 1986 for this invention. In this new kind of microscope, electrons are speeded up in a vacuum until their wavelength is extremely short. Beams of these amazingly fast electrons are focused on a cell sample and are scattered or absorbed by the cell’s organs. This forms an image on electron-sensitive photographic plate of its structure.
http://www.microscopesguru.com/when-was-the-microscope-developed/
http://inventors.about.com/od/mstartinventions/a/microscope.htm
http://www.brianjford.com/whistmic.htm
http://www.microscope-microscope.org/basic/microscope-history.htm
http://campus.udayton.edu/~hume/Microscope/microscope.htm