1) English invention
Found on
https://www.crosswordclues.com/clue/balance-spring
A balance spring, or hairspring, is a spring attached to the balance wheel in mechanical timepieces. It causes the balance wheel to oscillate with a resonant frequency when the timepiece is running, which controls the speed at which the wheels of the timepiece turn, and thus the rate of movement of the hands. A regulator lever is often fitted, whi...
Found on
http://en.wikipedia.org/wiki/Balance_spring
(from the article `watch`) Controlling the oscillations of a balance with a spring was an important step in the history of timekeeping. English physicist Robert Hooke designed ...
Found on
http://www.britannica.com/eb/a-z/b/10
An alternative name for the hairspring.  The latter term is preferred in the U.S.A. but is not unknown in Britain;  in 1857 the humorous writer Tom Hood used the name ‘Harespring` [sic] for a watchmaker.
Found on
http://www.encyclo.co.uk/local/20450
No exact match found.
