DEPARTMENT OF TERRESTRIAL MAGNETISM. 251 



As a result of the magnetic observations made on the Galilee and 

 the Carnegie, steady improvement in the magnetic charts of the various 

 hydrographic biu-eaus is becoming increasingly manifest. The latest 

 of these charts are the British Admiralty ' 'Curves of Equal Magnetic 

 Variation for 1917," in the construction of which credit is gi^'en to the 

 Department of Terrestrial Magnetism for the "principal part of the 

 new information now shown on these charts." 



OCEAN ATMOSPHERIC-ELECTRIC WORK. 



The first special report of Volume III (Researches of the Department 

 of Terrestrial INIagnetism), by L. A. Bauer and W. F. G. Swann, dealt 

 with the results of the atmospheric-electric work on board the Galilee, 

 1907-1908, and on the Carnegie, 1909-1916 (April). From the begin- 

 ning of the ocean work of the Department of Terrestrial Magnetism, 

 it has been its aim to include in the program of scientific work whatever 

 additional observational researches could be carried on advantageously 

 and profitably without conflicting with the prime object assigned to 

 the Department — the general magnetic survey of the globe. The 

 problem which naturally suggests itself as closely related to that of 

 terrestrial magnetism is that of terrestrial electricity, which embraces 

 the following subjects: (a) the electric currents circulating within the 

 Earth's crust; (h) the Earth's electric charge; (c) the conducting prop- 

 erties of the atmosphere. Subject (a) at present is one of combined 

 laboratory and observatory investigation (see page 254). Subjects 

 (b) and (c) together form the science termed '' atmospheric elec- 

 tricity." It is with regard to ocean observations and results in the 

 latter science that this special report concerns itself. A general elec- 

 tric survej^ of ocean areas possesses peculiar advantages over that 

 of land areas, not merely because of the greatly preponderating extent 

 of area, but because of the freedom from the disturbing influences of 

 topographic and cultural features. 



The Department's annual report for 1916 contained an abstract of 

 the chief results obtained during the period 1907 to April 1916. During 

 the summer of 1917 the discussion of the atmospheric-electric observa- 

 tions made aboard the Carnegie in the Pacific Ocean subsequent to 

 April 1916 was continued under the immediate direction of Dr. Swann, 

 who was assisted in this work chiefly by Dr. C. W. Hewlett. The 

 latter was connected with the Department during the summer of 1917 

 as a research assistant, and began an investigation to determine the 

 amount of radium contained in the sea-salt collected on the Carnegie's 

 fourth cruise. The method of investigation used was that suggested 

 by J. Joly. No such amount of radium in any of the samples collected 

 on the Carnegie at sea, far away from land, was found comparable with 

 that reported by certain former observers who used other methods 

 and whose samples were obtained over sea areas comparatively near 



