Progress with a Determination of the Speed of Light
A programme at the National Physical Laboratory is in progress for the purpose of making a determination of the speed of light (c) to an accuracy of one in 108 by measuring the frequency and wavelength of an infra-red laser emission. This accuracy is essential if the value for c is to be used to unify the standards of frequency and length, the former being at present realizable to one in 1012 and the latter to one in 108. The presently accepted value is 299 792.50 ± 0.10 km s−1 as determined by K.D. Froome at the National Physical Laboratory (Proc. Roy. Soc.,A247, 109 (1958)).