A method for accurate measurement of short-time intervals

A method for accurate measurement of short-time intervals

Author: Curtis, H.L. Duncan, R.C.

Year: 1923

The method consists in producing simultaneously on a moving photographic film a record of the occurrence of the events under consideration and timing lines from a tuning fork acting as a shutter. This shutter consists of two opaque vanes, in which narrow slits have been cut, mounted on the prongs of a tuning fork, so that the slits are parallel to the axis of the fork, and coincide when the fork is at rest. When the fork vibrates the two slits will coincide twice during each complete period of the fork. The shutter is brilliantly illuminated, and the light which passes through as a flash when the shutter is opened is focused on the film by means of a suitable optical system. The accuracy depends on the accuracy of the tuning forks, of which there are three classes: (1) Self-driven forks; (2) forks driven by a master fork; (3) freely vibrating forks. These are all discussed. Very satisfactory results have been obtained by using a 100-cycle fork to drive a 500-cycle fork. For problems demanding the highest precision obtainable, however, this method is not satisfactory. The inaccuracies of the preceding method can be reduced, by using a comparator, to a few millionths of a second. The