A Measurement of the Velocity of Light

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Abstract
A method is described for measuring the velocity of light with a relatively short base line. A Kerr cell modulates a light beam at very high frequencies and a photoelectric cell is used for detection of the modulations. The modulated light beam is divided into two portions by means of a half-silvered mirror and the two parts sent over different optical paths. By noting the difference in path length required to produce a minimum of voltage in the tuned circuit of the photoelectric cell, and the frequency of modulation of the light, it is possible to measure the velocity of light with considerable precision. Modifications of this method are described and the theory developed. The mean result of a series of measurements involving 651 observations is given as 299,764 km/sec. ±15 km/sec. in vacuum.