Clock

an instrument for measuring and indicating the time of day. The first measure of time was the sundial, followed by the hour-gla ; next the clepsydra, or water clock. These have been in use 2,000 years. ‘The next improvement was the substitution of a weight for the water. A pendulum was added about A. D. 1000. The anchor escapement, invented in 1666-1680, and the dead beat escapement in 1700, gave a new impulse to clock making. There has been no material change in the principles on which clocks are made, except in the substitution of steel springs for weights and in the finer movements, and in the addition of the hair-spring to regulate still further the action of the escapement or pendulum, since 1700.