A method for the accurate measurement of short-time intervals
Harvey L. Curtis, ROBERT C. DUNCAN · Scientific Papers of the Bureau of Standards · 1922
A method is described whereby the time between two events which occur less than a second apart can be determined with a high degree of accuracy.The method con- sists in ruling on a moving film a uniform time scale simtdtaneously with the recording of the events to be studied.The time scale is obtained by throwing flashes of light on the film, the interval between flashes being governed by a special shutter fastened directly to and operated by the prongs of a tuning fork.The shutter consists of two slotted, aluminum vanes moimted, respectively, on the two prongs of a timing fork, the slots being parallel to the axis of the fork and so adjusted that when the tuning fork is at rest the vanes overlap and the slots coincide.As the fork vibrates the slots coincide twice during each vibration, and thus form a shutter whose frequency is twice that of the tuning fork.The shutter is brilliantly illumi- nated, 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.Very satisfactory results are obtained using a 500-cycle fork, driven by impulses from a loo-cycle fork.This divides the film in thousands of seconds and makes it possible to read time intervals directly from the film with the tmaided eye with an error of not more than one ten-thousandth of a second.By using a comparator the error is reduced to a few millionths of a second.The article includes a complete discussion of the necessary conditions for the best results, the sources of error inherent in the method, and the accuracy which may be expected. CONTENTS.Page.' First described by Lockler and BoltzmaninAnn.d. Phys.u.Cbem., 141, p. 321; 1870.' See Dadourian, loc.cit., for a list of observers and the values they obtained.Some of this data is on driven forks, but there seems to be no difference in the temperature coefl&cient of driven and freely vibrating forks.