The phonic chronometer
A B Wood, J. M. Ford · Journal of Scientific Instruments · 1924
A description is given of an electrically controlled chronometer which is capable of directly indicating time-intervals with an accuracy of one-thousandth of a second. The chronometer is driven by a powerful phonic motor, of novel design, which is controlled by a tuning-fork of adjustable frequency. Methods of eliminating and compensating errors are dealt with and accuracy tests are described. The chronometers have been used in ( a ) the accurate measurement of time in physical investigations, e.g. variation of period of a compound pendulum with amplitude of swing, velocity of sound in the sea, ( b ) sound-ranging, depth sounding, and in hydrographical survey, ( c ) psychological measurements - reaction times, etc., ( d ) motor-car speed events, ( e ) electrical investigations involving measurements of quantity (current × time). The instruments are robust in design and permit of simple manipulation of all parts requiring adjustment.