DEPARTMENT OF TERRESTRIAL MAGNETISM. 305 



dissertation for the doctorate degree at the Technische Hochschule at 

 Munich, in 1913, Dr. Armstrong had developed the methods of Lagrange 

 with numerous applications, first, to computed values of an assumed 

 periodic function, for the purpose of testing the powers and limitations 

 of the method, and, second, to observational data of suspected peri- 

 odicity. A preliminary application of the method was made to mag- 

 netic data (diurnal range of the magnetic declination at three European 

 stations) during the period 1841 to 1910, as also (chiefly for the same 

 period) to the Wolf-Wolfer sun-spot numbers. 



For the magnetic data three periods, respectively of about 11.4, 22, 

 and 70 years, were found. Periods of about the same length were 

 disclosed by the sun-spot data. As in the present work the data were 

 combined into 5-year means, shorter periods than the one of 11.4 years 

 could hardly be detected. The investigation is being continued. 



ATMOSPHERIC ELECTRICITY. 



Notable progress, it is believed, has been achieved by the Depart- 

 ment, during the present year, by the theoretical and experim.ental 

 researches of Dr. W. F. G. Swann. In the experimental work he v/as 

 assisted by Dr. C. W. Hewlett and Mr. H. F. Johnston. Five articles 

 by Dr. Swann (see pages 328 and 332) have appeared, in which new 

 points of theory were brought out, serious errors in certain instruments 

 were made known, and improved methods and instruments were devised. 

 As a result, considerable improvement has been made in the work in 

 atmospheric electricity aboard the Carnegie, on her third cruise. 



It is now deemed worth while to expand the work of the Department 

 in this subject in two directions: (a) continuous observations, by self- 

 recording means, in atmospheric electricity and radioactivity, at the 

 Department's laboratory in Washington and at such observatories 

 elsewhere as the Department may be able to establish in the near 

 future; (&) a general electric survey of the globe, implying observa- 

 tions at points distributed over the Earth's surface, somewhat as in a 

 magnetic survej^ 



Probably the late Professor Rowland was one of the first, in his 

 address before the Congress of Electricians, held at Paris, September 

 1881, to point out the need, in atmospheric electricity, ''of a series of 

 general and accurate experiments performed simultaneously on a por- 

 tion of the Earth's surface as extended as possible."^ He says that 

 "the principal aim of scientific investigation is to be able to understand 

 more completely the laws of nature, and we generally succeed in doing 

 this by bringing together observation and theory." On Professor 

 Rowland's motion, the Congress resolved "that an international com- 

 mission be charged with determining the precise methods of observation 



^Physical Papers of Henry A. Rowland, Baltimore, 1902, p. 212 et seq. 



