Third International Congress for applied mechanics

Measurement of the Velocity of Light by the Use of the Kerr Electra-optical Effect. 0. MITTELSTAEDT. (Ann. der Phys., NO. 2, 1929.) Fizeau in the nineteenth century measured the velocity of light by sending a beam between two teeth of a revolving wheel to a mirror. From this it was reflected back along the same path. With properly related length of light path and speed of rotation the returning beam was caught upon the cog which had moved up to intercept it while it was going to the mirror and returning to the wheel. From the time and the distance the velocity was calculated., This method is subject to serious difficulties in the measurement of the path of the light, about 40 km., and of the speed of rotation of the wheel which for the success of the observations had to be variable. In 1925 Karolus made use of the Kerr magneto-optical effect instead of a mechanical means of interrupting the beam. Thus increasing the frequency of interruption to IO,OOO,OOO per sec. he reduced the path of the beam to 15 meters. In the present investigation the method is modified and improved. The velocity of light is calculated to be 299,778 km. per sec. Michelson has found 299,796 f 4 km. per sec. G. F. S.

Third International Congress for Applied Mechanics will be held at Stockholm, Sweden, August 24 to 29,193o. The opening meeting will be held at the Royal Academy of Engineering Sciences and regular sessions will be at the Royal Technical University. The following subjects will be discussed: hydrodynamics; the theory of propulsion and the problem of resistance; elasticity and the strength of materials; oscillations of ships and vehicles, and acoustics of space and similar questions. A complete program will be announced later. Inquiries concerning the Congress should be sent to the Secretary, Prof. W. Weibull; Kgl. Tekniska Hogskolan, Stockholm, Sweden. R.