Hooke's law apparatus. Artwork by Robert Hooke (1635-1703) of the apparatus used in his experimental work on devising Hooke's law. Hooke's law relates the effects on bodies of stress and strain, and states that the extension of a spring is proportional to the force applied within the elastic limit. Here, the spring can be seen with a tray attached beneath it for receiving different weights. Hooke was a great inventor, and amongst other things he realised that a spiral spring could control a clock, coined the term cell" on viewing wood through a microscope, and invented a universal joint. He was also a Surveyor of London, involved in rebuilding after the fire of 1666."