Hooke's spring, c 1679.
© Science Museum / Science & Society Picture Library
From 'Lectiones Cutlerianae' by Robert Hooke (1635-1703). This diagram is used to demonstrate Hooke's Law. This is that the strain placed on an elastic body is directly proportional to the stres produced. In the diagram the coil of wire (AB) is suspended from one end (C) and different weights are placed in the pan (E) hanging from the other end of the coil (D). This work later led to the invention of the balance spring, which made the pocket watch posible, and analogue weighing machines.