What is the relation between the iris diaphragm in cameras, the universal joint used in motor vehicles, and the balance wheel in a watch?

All invented by Robert Hooke

Hooke's inventions also include the spirit level, the compound microscope, sash windows, and telescope crosshairs. "Indeed, Hooke coined the biological term cell -- so called because his observations of plant cells reminded him of monks' cells which were called 'cellula'." (W) Quite a guy. Good one, mozart!

Another hit for Jenny. Thanx Professor.