Lever escapement, c 1650.
© Science Museum / Science & Society Picture Library
Detail of mechanism. This model is an example of the most important type of watch escapement - the balance wheel mechanism. In this mechanism, the impulse from the escape wheel is transferred to the balance by two levers. This type of escapement was used by Christian Huygens (1629-1693), the important Dutch physicist, in his balance spring watch of 1675.