Robert Hooke was a British scientist who made significant contributions to the field of microscopy. He designed his own light microscope, which used multiple glass lenses to light and magnify specimens. Hookes reputation in the history of biology largely rests on his book Micrographia, published in 1665, where he described and illustrated what he saw under his microscope. Some of Hookes images were so curious and extraordinary that people refused to believe they were real. While observing cork through his microscope, Hooke saw tiny boxlike cavities, which he illustrated and described as cells. He had discovered plant cells, which led to the understanding of cells as the smallest units of life and the foundation of cell theory. Hooke also observed organisms as diverse as insects, sponges, bryozoans, foraminifera, and bird feathers.