It has been known for a long time that a 'free' pendulum clock will achieve perfect timekeeping. A pendulum, to achieve this, would maintain its arc and do no work, without ever receiving impulse - perpetual motion, clearly impossible! Early this century, William Hamilton Shortt, in collaboration with Frank Hope-Jones, prouced an almost free pendulum clock system which was used as the time standard in observatories throughout the world until superceded by the quartz-crystal clock in the late 1930s. Briefly, in the Shortt clock system, a synchronome master clock is used as a slave. The master free pendulum receives impulse released by the slave clock and in turn controls the slave clock's rate by a hit and miss governor. The master pendulum operates in a steel cylinder at a constant temperature and reduced atmospheric pressure; small changes in operating pressure are used to make minute adjustments to rate by air-friction loss and circular error.