CORK. Robert Hook discovered cells in 1665 with the help of a 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.The Law of elasticity was discovered by him in 1660, which STATES that the force needed to extend or COMPRESS a SPRING by some distance is proportional to that distance.