830 Prof. Hansteen on the Number and Situation 
by the north pole of the earth, the south magnetic pole ; and re« 
pelied from the south by the earth’s south pole, the north mag- 
netic. The reverse of this takes place with regard to the south- 
ern half of the needle. The position of the needle thus depends 
on this double attraction and repulsion. If, over the whole sur- 
face of the globe, the magnetic needle pointed due north and 
south, w^e should at once conclude that the earth’s magnetic 
poles coincided with its geographical. But, after men had been 
acquainted with the use of the compass for 200 years, it was 
found by more accurate observation, that the direction of the 
needle declines from the meridian, which declination is called the 
Variation of the Compass^. It was farther observed, that this 
variation was different, at different parts of the earth ; in one 
place to the east ; in another to the west ; and, at last, at a later 
period, that, at the very same place, this variation was not the 
same at different times. This remarkable phenomenon can be 
explained in no other way, than by supposing, that the magnetic 
poles are situated at a considerable distance from the poles of 
the earth’s revolution ; and that these poles, from one year to 
another, are changing their position. But as there are natural 
magnets which have four poles, two of each name, it is not im- 
possible, that the earth may be found to be such an anomalous 
magnet. Here, then, arise the two following c|uestions to be 
solved. Are two magnetic poles sufficient to explain all the phe- 
nomena of the variation of the compass, or are we under the ne- 
cessity of assuming more What are the position and motions 
of these poles ? 
It may he asserted, without any extravagance, that the inven- 
* The first discovery of the variation of the compass is commonly ascribed to 
Columbus, who, among other perplexities he had to suffer from his mutinous crew, 
was questioned by them whether, at such a distance from the parts of the earth 
hitherto known, thq compass might not point to quite other directions than north 
and south, and thus mislead, instead of guiding their course. To satisfy them on 
this matter, he observed the setting of the sun, and found that the needle actually 
deviated two degrees from the meridian. It was half a century after this before 
the exact amount of the variation was known. That it was so lately discovered 
in Europe, and not at all known in China, where the compass had been longer 
known, may be accounted for from Ibis,— that in Europe it was at that time very 
small, and in China, for these 200 or 300 years, in some places nothing, and no- 
where exceeded 2°. 
