Why? The Science of Athletics

186 WHY?-THE SCIENCE OF ATHLETICS to a hundredth or even a thousandth of a second, such precision being regarded as necessary since, even at the end of a half-mile race, men have been known to cover a yard in a tenth of a second. The preliminary requirements to be satisfied in carry– ing out the experimental work were the use of a precision of .o I, as this would be accurate to within 3 or 4 ins. in giving the position of a runner ; the use of a photographic method of recording ; and a means of photographing the reading of the clock at the finish to show the runner's actual time. Therefore the clock had to be set at zero before the start of each race and must be started simul– taneously with the firing of the pistol. The Bell Telephone Laboratories designed a tuning-fork generator and a motor-driven clock to meet these requirements. In order to meet the requirements of spectators, who would not want to wait upon the development of a film to hear the time in which a race had been run, it was decided to make two clocks. The one in which the time and position of the runner could be photographed adjacently on the same film; the other to be hand– stopped by a timekeeper to give a reading to the nearest hundredth, subject only to human error in finally actuating the clock, so that the time might be at once announced. The system, as finally evolved, consists of a 200 cycle tuning-fork generator driving a synchronous motor at a speed of ten revolutions per second. The motor shaft is connected to a clock mechanism by means of a magnetic clutch so arranged that the clock dials are set in motion by the firing of the starter's pistol. The camera is standard 16 mm. and takes 128 pictures per second. Most of the picture area is devoted to the action of the competitors, but the three rotating dials of the timing apparatus are also photographed as they pass a fixed hairline. This makes it possible to obtain the time on the film in the largest practicable characters, since only sm~ll segments of the entire dial arrangement need be photographed. The three concentric dials show hundredths, seconds and I