LI. A. Bauer— Variation of Terrestrial Magnetism. 191 
attempting the unraveling of the greatest secret of all—the 
origin of the so-called permanent magnetism. 
Thus many plausible theories advanced by eminent and care- 
ful philosophers have been shown to be inadequate. Very fre- 
quently electrical hypotheses have been proven false by reason 
of the fact that the theoretical induced currents would not 
proceed in the requisite direction. As Ampére first pointed out, 
the observed approximately northward direction of the magnetic 
needle necessitates electric currents (if they be the cause of 
the needle’s polarity) flowing in an east-west direction. As yet 
no satisfactory theory has been advanced to account for such 
induced east-west currents. The thermo-electric hypothesis 
met with considerable favor at one time and was adopted by 
eminent geomagneticians. It has, however, been discarded by 
prominent physicists. 
If we have induced currents, then it would appear that 
according to Gauss’s Potential Theory of Terrestrial Magnet- 
ism, we must look for them in the earth’s crust, not in the 
atmosphere. It will be recalled that his beautiful investiga- 
tions proved : 
first, that by far the greater portion of the earth’s mag- 
netic force possesses a potential. 
Second, that the seat of the so-called permanent magnetic 
force is within the surface. 
It is a well-known fact that we have earth currents, directed 
roughly N.E. to 8.W., which experience fluctuations concom- 
itant, or nearly so, with a freely suspended magnetic needle. 
A number of investigators believe themselves to have shown 
conclusively that these earth currents are noé sufficient to pro- 
duce the observed phenomena of the earth’s magnetism. This 
is a matter of difficult experimental determination. A fact 
clearly indicated, however, is that earth (and atmospheric) 
current observations should be more carefully and more 
Frequently made than hitherto and that they should form as 
much a part of the regular work of a magnetic observatory as 
the observations of the deflections of a magnetized needle. 
Enough has been given in the preceding remarks to show 
how infinitely complex and well-nigh hopeless is the solution of 
the question as to the origin of the earth’s magnetic field. 
It is not any more necessary, however, for us to answer this 
puzzling enigma in order to make headway in the study of ter- 
restrial magnetism, than it is for the astronomer to know, for 
example, the origin of the moon. He knows the moon exists, 
and so he determines its disturbing influences upon the earth’s 
motions. 
Just so is it with geomagnetism. We do not know the 
whence but we know its existence. Let us then accept it as part 
