204 LZ. A. Bauer— Variation of Terrestrial Magnetism. 
0:058xXa@ ft 
a ee ee 
tae Oe 305 Ka ae q 
mer 0 hence w=. 101 
or the equatorial inclination of the actual magnetic axis would 
be about 80°. The latest computation based on the Gaussian 
potential theory gave a value of 78°-3. The close coincidence 
is certainly striking. 
Henee, 
The principal phenomena of the distribution of terrestrial 
magnetism can be regarded as produced by two rectangular 
magnetic systems, a polar and an equatorial, the former of 
about 5 or 6 times the strength of the latter. 
Since, in going around the earth along a geographical paral- . 
lel of latitude, the deflections due to the secondary system. 
almost balance each other, as shown by the fact that the mean 
elements so nearly agree with the computed ones of the pri- 
mary polar system (see table, p. 196), the inference might be 
drawn that the secondary field 1s in some way connected with 
the earth’s rotation. : 
In a subsequent number of these contributions, this matter 
will be examined in detail from a theoretical standpoint. For 
this reason, I shall make no attempt in the present paper to 
resolve the complex secondary magnetic system shown on the 
diagram into its components. The field as exhibited may 
really be a resultant one of three—a theoretical equatorial 
field, a field due to electric currents piercing the earth* and a 
third, due to the heteorogeneity of the earth’s composition. 
*Such currents have been made probable by Dr. A. Schmidt’s beautiful 
researches. (See his brief note in Report of the Brit. Ass. for Adv. of Science, 
for 1894, p.570.) They may be due to the following reason: 
If an arbitrarily magnetized sphere rotates in a conducting fluid, the surface of 
contact of sphere and fluid being also conducting, currents will be incited in the 
fluid which pass into the sphere, suffer a deflection and then pass out again. 
While in the case of the earth, there is perhaps no fluid with respect to which the 
solid earth performs a complete differential rotation, there are partial differential 
rotations, due to moving streams, ocean currents, tidal waves and air currents. 
In the latter case it is also quite possible to have complete differential rotations 
if we take into consideration the mighty polar whirls of the primary atmospheric 
circulation. See also quotation with respect to Professor Schuster’s work, p. 192. 
Washington City, June 4, 1895. 
