DEPARTMENT OF TERRESTRIAL MAGNETISM. 247 



for long-distance flying the aviator should be able to locate his position, for 

 example, by astronomical observations or directional radio bearings, when he 

 is unable to see objects on the ground during night flights or while flying above 

 clouds or fog. The paper describes work during the latter months of 1918 

 at Langley Field in the attempt to develop methods and instruments for 

 navigating airplanes by astronomical observations (see Year Book for 1919, 

 pp. 302-304) , But owing to difficulties of navigation by astronomical methods 

 and to the fact that frequently no celestial body can be seen, a third method of 

 navigation by some directional radio device seems to be the most promising 

 solution of the problem. This method is as yet in the experimental stage. 



Effects of a total solar eclipse on the Earth's magnetic and electric fields. ^ J. P. Ault. 



The occurrence of a total solar eclipse furnishes an opportunity to study 

 variations in the Earth's magnetic and electric fields which may be caused by 

 a definite known phenomenon. Thus, data may be obtained which will be of 

 assistance in the solution of outstanding questions in terrestrial magnetism 

 and atmospheric electricity. 



The first determined and systematic attempt to ascertain whether there was 

 an appreciable effect on the Earth's magnetism during a solar eclipse was made 

 in 1900, at Dr. L. A. Bauer's initiative and under his direction. A large mass 

 of valuable data has been obtained during the various total solar eclipses since 

 that date, chiefly through the efforts of the Department of Terrestrial Mag- 

 netism of the Carnegie Institution of Washington. Observations of the 

 variations in atmospheric electricity during a solar eclipse were made as early 

 as 1898, but only in recent years has the attempt been made to obtain syste- 

 matic and extensive electric observations during solar eclipses. 



The magnetic and, in part, the electric effects during solar eclipses which 

 may be predicted by theoretical considerations have been verified to a remark- 

 able degree by the observational results. The conclusion seems to be justified 

 that the screening of a part of the Sun's radiation from the Earth's atmosphere 

 due to the Moon's presence between the Sun and the Earth interrupts the 

 march of the usual daily variation in the Earth's magnetic field. The effect, 

 though quite small, has been positively identified in cases when conditions 

 were favorable, e. g., absence of cosmical magnetic storms. The magnitude of 

 the effect depends upon the length of maximum obscuration, distance from 

 the belt of totality, and position of the station in the portion of the Earth 

 covered by sunlight at the time of the eclipse. 



The preliminary discussion of the results obtained during the eclipse of 

 September 10, 1923, at Point Loma, at Mount Wilson, and at Guatemala 

 City, confirms previous conclusions regarding possible eclipse magnetic and 

 electric effects. 



Magnetisierung, Rotation, und Atomstruktur. S. J. Barnett. Physik. Zs., vol. 24, 14 

 (January 1923). 



In the Physikalische Zeitschrift for August 1, 1922 (p. 307), W. Braunbek 

 develops a theory of rotation by magnetization on the assumption that the 

 nucleus is involved as well as the outer electron system, for each orbit of which 

 the ratio of angular momentum to magnetic moment is 2ml e. 



The theory given by Braunbek is essentially identical with that published in 

 1908 by O. W. Richardson ^ and used by J. Q. Stewart ^ in 1917 for the same 



^ Presented at the Los Angeles meeting of the American Association for the Advancement of 

 Science, before the joint meeting at Pasadena of the American Physical Society with the Amer- 

 ican Astronomical Society, the Astronomical Society of the Pacific, and of Section D, September 

 18, 1923. 



"^ O. W. Richardson, Phys. Rev., vol. 26, 1908 (24). 



*J. Q. Stewart, Phys. Rev., vol. 11, 1918 (100). 



