Robert Hooke made contributions across many fields of science, but his principal contribution was in the field of biology. Hooke published a book called "Micrographia" in which he detailed observations and experiments with light microscopes.
Robert Hooke lived and worked primarily during the 17th century. He developed a compound microscope and complementary light source that was among the best of his era. He used this array to make detailed observations of insects, sponges and feathers.
Hooke also used his microscope to study thin slices of cork. He observed that the cork was comprised of tiny, box-like sections that reminded him of the cells in a monastery. Due to these observations, he coined the term "cell" for the functional units that make up living things. When Antony van Leeuwenhoek reported his discovery of bacteria and protozoa, that he called "little animals," Hooke was asked to confirm the observation.
Robert Hooke also discovered the Hooke's law of elasticity, named after him. Hooke's law states that the force required to compress or extend a spring by a given distance is proportional to that distance. Hooke's law is also applicable in other situations, such as a plucked guitar string or the force of wind on tall buildings.