290 CARNEGIE INSTITUTION OF WASHINGTON. 



of Terrestrial Magnetism with the various pubhcations by the observatory, 

 as well as recent data in manuscript. In his letter of October 10, 1921, he 

 stated that "he hoped by cooperation with some American observatories to 

 get data for practically every day in the year." It will thus become ulti- 

 mately possible to obtain from solar-prominence observations desired data 

 for supplementing the measure of solar activity derived by Mr. Bauer from 

 the sun-spot numbers, which measure, it will be recalled, was found more 

 useful, in general, than the sun-spot numbers direct, for disclosing relationship 

 between solar activity and magnetic and electric phenomena. Mr. Bauer 

 also reported having received a letter from Professor Wolfer, kindly offering 

 to supply regularly, in advance of publication, the sun-spot tables to the 

 Department of Terrestrial Magnetism. Professor Wolfer has expressed a 

 favorable opinion as to the suitability for short-interval comparisons of the 

 D-measure (average departure) of solar activity, used in Mr. Bauer's investi- 

 gations. 



In view of the fact that the Department of Terrestrial Magnetism is plan- 

 ning to install earth-current lines at its magnetic observatories, a discussion 

 of the existing earth-current observations was undertaken. From the series 

 of earth-current observations, 1910-1920, made at the Observatorio del Ebro, 

 Tortosa, Spain, interesting relations have been found between earth-currents, 

 terrestrial magnetism and electricity, and solar activity. (See abstract, pp. 

 290-291.) 



In connection with the investigations as briefly outlined, it has been found 

 desirable to obtain some meteorological quantity also which could be utilized 

 in the study of relations between certain meteorological and other geophysical 

 phenomena, and solar activity. Mr. Bauer is at present trying out for this 

 purpose the "time barometric gradient" (differences of pressure, divided by 

 the elapsed time-interval) as obtained from the recorded pressures at various 

 stations. 



Mr. Marvin reported as to how the space barometric gradients might be 

 used in attempts to find relationship between meteorology and solar activity, 

 and submitted a subreport on the subject. 



Mr. Abbot reported upon the solar-constant observations now in progress 

 under the auspices of the Smithsonian Institution. 



Some results of recent earth-current observations and relations with solar activity, terres- 

 trial magnetism, and atmospheric electricity.^ Louis A. Bauer, Terr. Mag., 

 vol. 27, 1-30 (March-June 1922). 



The Department of Terrestrial Magnetism is planning to install earth- 

 current lines for sj^stematic observations at its magnetic observatories. This 

 year such lines are to be installed at the Watheroo Observatory, Western 

 Australia, and later at the Huancayo Observatory, Peru. 



Various initial investigations concerning best methods of earth-current 

 measurements have been in progress at the Department's laboratory. To 

 Mr. 0. H. Gish, appointed January 1, 1922, Associate Physicist of the Depart- 

 ment, has been assigned the continuation of these investigations. Further- 

 more, in order to take advantage of the previous experience gained in such 

 work, and to ascertain the direction in which further study is desirable, a 

 discussion of the available data, especially for the 11-year series at the Obser- 

 vatorio del Ebro, was undertaken by the writer. Assistance was received 

 from Messrs. Duvall, Ennis, and Peters, and from Miss Tibbetts. 



For the first time comparisons could be made between the phenomena of 

 terrestrial magnetism, earth-currents, and atmospheric electricity, as observed 



> Presented before the Philosophical Society of Washington, February 25, 1922. 



