An earlier Paper (Proc. Phys. Soc., Vol. 26, 1914, p. 137) discussed a number of data for the times of occurrence of the "Sudden Commencements" (S.C.s) of magnetic storms which had been published by Dr. L. A. Bauer in "Terrestrial Magnetism," and came to a conclusion adverse to Dr. Bauer's claim that S.C.s were propagated from east to west or west to east, with velocities of from 100 to 200 kilometres per second. Since that date Papers on the subject have been published by Prof. S. Chapman and Fr. Rodés, of the Ebro Observatory, propounding theories differing from one another and from Dr. Bauer's. In a recent Paper Dr. Bauer and Mr. W. J. Peters have re-discussed the subject. They conclude that the motion in longitude is much more rapid than according to Dr. Bauer's original estimate, and suggest that is is really a case of propagation from the magnetic equator towards either magnetic pole.
The Section of Terrestrial Magnetism and Electricity of the International Union of Geodesy and Geophysics has recently approved a scheme aiming at the construction and use of special instruments to find out whether S.C.s have a finite rate of propagation. The present Paper discusses the whole subject, partly with a view to facilitating a decision as to the new apparatus and the stations most suitable for the investigation.