Robert Hook discovered cells in 1665 with the help of compound microscope.
A cell is a basic unit of life.
The structure observed by Robert Hooke under the microscope was a slice of cork.
When he looked at a thin slice of cork under his microscope, he saw the structure like a honeycomb.
Law of elasticity was discovered by him 1660, which states that the force needed to extend or compress a spring by some distance is proportional to that distance.