Hans and Zacharias Janssen made the first microscope by placing two lenses in a tube
Robert Hooke studied various objects wiht his microscpe and published his results in microscopia.
Anton van Leeuwenhoek used a simple microscope with only one lense to look at blood, insects and other objects.
Robert Brown contributed to the cell theory
Schleiden became the first to formulate what was then an informal belief as a principle of biology equal in importance to the atomic theory of chemistry.
Microscopical Researches into the Accordance in the Structure and Growth of Animals and Plants, was published
first accurate account of apical cells.
He pioneered the modern concept of pathological processes by his application of the cell theory to explain the effects of disease in the organs and tissues of the body. He emphasized that diseases arose, not in organs or tissues in general, but primarily in their individual cells. Moreover, he campaigned vigorously for social reforms and contributed to the development of anthropology as a modern science.
Ernst Ruska develops the electron microscope. The ability to use electrons in microscopy greatly improves the resolution and greatly expands the borders of exploration.