Vol. 6, 1920 
GEOPHYSICS: L. A. BAUER 
573 
of the chief outstanding problems in terrestrial magnetism. This problem 
involves the question whether or not the magnetic forces of the earth 
can be entirely referred to a potential. If not, then the question arises 
as to the existence of vertical electric currents, which will be of interest 
both to students of the earth's magnetism and of the earth's electricity, 
using the latter term in its most general sense so as to include electric phe- 
nomena arising from systems both below and above the earth's surface. 
The ocean work of the Department of Terrestrial Magnetism has been ar- 
ranged with the special view of obtaining the requisite data for the solu- 
tion of this interesting question. But for the war all the necessary data 
and the results of their discussion would be available now. 
2. Analysis of Continental and Regional Magnetic Fields: The detailed 
magnetic survey of the United States — the largest land area over which 
magnetic surveys with the requisite accuracy and detail have been made — 
affords further opportunity for the investigation of the problems referred 
to in the previous paragraph, at least so far as the investigation of those 
problems can be undertaken for a limited region of the globe. In the re- 
spect that the magnetic constants of the earth's general field depend in 
a very large measure upon the area embraced in the investigations, prob- 
lems of terrestrial magnetism differ fundamentally from those of geodesy. 
Concerning this point, a preliminary study was made by the writer in 
connection with a brief discussion of "Some Results of the Magnetic 
Survey of the United States" printed in Science, May 22, 1908, (812-816). 
It was found that the magnetic forces observed at any given point in 
the United States are the resultant effects of (1) a general or terrestrial 
magnetic field arising from the general magnetic condition of the earth, 
(2) a general, terrestrial disturbing cause which distorts the general mag- 
netic condition of the earth at the place of observation, related possibly 
in some manner to the rotation of the earth, (3) a continental disturbing 
effect, arising largely from that portion of the North American continent 
above the general ocean bed, (4) a regional disturbance caused by low-lying 
magnetized masses or earth-currents covering a certain region, and (5), 
a local disturbance to be referred to magnetized masses or currents in 
the immediate vicinity. 
A mathematical formula of limited spherical harmonic terms based 
upon the entire earth cannot, of course, include also disturbances of such 
restricted areas as are embraced under Nos. 4 and 5, namely, regional 
and local disturbances, but it appears that such a formula cannot ade- 
quately represent even the continental eifects. In the spherical-harmonic 
formulae the t'erms of the various orders advance and recur by trigono- 
metric functions of multiples of the longitude and the latitude. Thus 
a term involving six times the longitude is supposed to continue around 
the earth six times in unaltered manner. However, such a term arising, 
for example, from the North American continental shelf, which in the 
