334 
LITTLEHAtES. 
We do not know why the earth should act like a magnet, 
but we are aware that the observed manifestations could only 
be caused by magnetized matter or electric currents within 
the substance of the Earth, or by electric currents in the 
region outside of the Earth; and one of the first fruits of the 
expression of the magnetic potential of the Earth in terms 
of spherical harmonics was the proof that the principal seat 
of activity of the causes which produce the observed facts 
of terrestrial magnetism is located inside of the crust of 
the Earth. 
The endeavors of most of the early investigators into the 
nature of the Earth’s magnetism to express its manifesta¬ 
tions as the result of one or more bar margets utterly failed 
to account for the complications of the actual facts of obser¬ 
vation. The earth is a very irregularly magnetized magnet 
with a pole similar to that which we call the south pole of 
the magnet, somewhere in the north of North America and 
an opposite pole somewhere in the Antartic region, but not 
at opposite ends of a diameter. 
If the Earth w'ere magnetized uniformly in the same di¬ 
rection throughout its interior, the potential would be a 
harmonic of the first degree, the magnetic meridians would 
be great circles passing through two magnetic poles diamet¬ 
rically opposite, and the magnetic equator would be a great 
circle. 
One proof of the futility of the attempts of the older 
philosophers to explain the distribution of the Earth’s mag¬ 
netism on the hypothesis that the Earth contained some-' 
thing like a bar magnet is the fact that there are two places 
in the northern hemisphere—one in the north of Canada, 
and another in the north of Siberia—where the terrestrial 
magnetism has a maximum force. These are called the 
magnetic foci. Generations ago leading authorities, reason¬ 
ing by induction, contended that the observed facts could 
not be explained without admitting that there are two 
systems of magnetism superposed—one having reference to 
the stronger focus in Canada and the other to the weaker 
