UNDER the title “Die Variationen des Erdmagnetismus” Prof. Ernst Leyst has written a paper, occupying 250 pages and four plates, in the Bulletin de la Société Impériale des Naturalistes de Moscou for 1909. It deals with magnetic data from the Russian observatories at Pavlovsk (St. Petersburg), Irkutsk, and Katharinenburg, and with some corresponding data from Potsdam and Greenwich. The paper contains valuable statistical data for Pavlovsk, such as the secular changes of all the magnetic elements from 1873 to 1906, and diurnal inequalities derived from a 33-year period. Its main object, however, is to investigate the relations borne to terrestrial magnetism by sun-spot frequency and barometric pressure. A number of the data bearing on the sun-spot connection should be useful, such as diurnal inequalities in years of sun-spot maximum and minimum at the several stations. But their utility would have been greater if the numerical relationships between magnetic and solar phenomena had been gone into more critically. A good deal has been already done on these lines, even for some of (he stations considered by Dr. Leyst, of which he seems unaware.