GEOPHYSICS: L. A. BAUER 
25 
(again chiefly of the magnetic declination), has not admitted always of 
direct physical interpretation, nor has it furnished always a convenient 
measure of the magnetic changes. Accordingly, the author in a pre- 
liminary examination of this relationship, made in 1909, introduced a 
quantity, called the 'local magnetic constant,' designated by G, which, 
under certain assumptions, is proportional to the magnetic moment of 
the earth, or to the intensity of magnetization. 
Various recent investigations have shown that the quantity, G, pro- 
vides an adequate measure of certain changes to which the earth's 
magnetism is continually subject. One interesting result of the 1909 
investigation was, that increased solar activity, as measured by sun- 
spot frequencies, was accompanied apparently, by a decrease in the 
earth's magnetic constant. This is the general effect which accompanies 
any large magnetic disturbance. For example, during the magnetic 
storm of September 25, 1909, the earth's magnetic state was below 
normal for a period of about three months. Since magnetic storms in 
general increase in frequency, as well as in magnitude, with increased 
sun-spot activity, the general effect on the magnetic constant during 
the sun-spot cycle is as it was found to be. 
In the present paper there are considered changes in the earth's 
magnetism of a considerably minor order of magnitude as compared 
with the magnetic perturbations just discussed; however, they are 
found to be not less important. The precise relationship between 
changes in solar radiation and possible changes in the earth's magnetism 
could be subjected to a definite examination only when values of the 
solar constant, of such accuracy as those of the Smithsonian Institution, 
became available. Fortunately, we now have a series of determinations 
at Mt. Wilson of this constant by Abbot for a period of four to five 
months during the years 1905 to 1914, excepting 1907. The 1913 
and 1914 data were kindly supplied by him, in advance of publication, 
for special use in connection with the present investigation. There 
were likewise made available the magnetic data for the same years, 
recorded at the observatories of the Coast and Geodetic Survey, for 
which acknowledgment should be made to the Superintendent of that 
Bureau. 
In the Balfour-Schuster theory of the diurnal variation of the earth's 
magnetism, it was necessary to introduce an additional hypothesis to 
account for the great ionization required by the theory, and solar radia- 
tion suggested itself as a possible cause. "Hence," Schuster says, "we 
might expect an increased conducting power in summer and in daytime 
as compared with that found during winter and at night." If solar 
