Vol. 6, 1920 
GEOPHYSICS: L. A. BAUER 
577 
solar eclipse of May 28, 1900, which occurred in the southeastern part 
of the United States, the writer being then in charge of the magnetic work 
of the Coast and Geodetic Survey. Nearly every prominent solar eclipse 
since then has been taken advantage of and cooperative observations 
over the entire globe have generally been made in accordance with a pro- 
gram outlined by the Department of Terrestrial Magnetism. Briefly 
stated, the general result has been that an appreciable magnetic effect, 
though of a minute order, is recorded during the period of a solar eclipse, 
similar in character to the variation experienced by the earth during a 
solar day, and differing from it only in magnitude. It is believed that 
the detection and study of an eclipse magnetic effect will be of great im- 
portance to theories of the earth's magnetic field and of its variations. 
During the famous solar eclipse of May 29, 1919, the Department of 
Terrestrial Magnetism had two expeditions in the belt of totality: at 
Sobral, Brazil, under the charge of D. M. Wise, assisted by A. Thomson; 
and at Cape Palmas, Liberia, under the writer's charge, assisted by H. 
F. Johnston. At Cape Palmas there was experienced the longest totality 
(6 minutes, 33 seconds) enjoyed by any of the eclipse parties. The geo- 
physical observations at the two stations will have an important bearing 
upon the complete interpretation of the light deflections observed by 
the British expeditions stationed at Sobral, Brazil, and the lie of Principe.^ 
Besides the magnetic results, interesting electric results were also ob- 
tained at Sobral, which, briefly stated, are:^ 
a. The potential gradient showed a well-formed minimum beginning 
with totality and extending until about 20 minutes after totality; the 
values observed during this period were about 20% lower than the mean 
derived from two equal periods immediately preceding and following it. 
b. During the period of potential-gradient minimum the fluctuations of 
the gradient were very much smaller than during the similar periods pre- 
ceding and following, c. The positive and negative conductivities (and, 
therefore, the total conductivity also), each showed an increase of the 
order of 20%, beginning just after totality and continuing for about 
15 minutes, d. The air-earth current density (product of simultaneous 
values of potential gradient and total conductivity) showed a greater 
constancy during the period in question than for any equal period through- 
out the forenoon of the day of the eclipse. 
The results for May 29, 1919, at Sobral, are in general agreement with 
those obtained at Lakin, during the eclipse of June 8, 1918,^ notwith- 
standing the great difference between the two stations as regards latitude, 
elevation, general topography, and distance from sea. 
7. Terrestrial Magnetism and Seismology: Records of seismic disturb- 
ances are frequently obtained on magnetograms and thus arise problems 
of joint interest with the Section of Seismology. Prof. Reid has made a 
special study of these magnetograph records and finds that the oscillations 
