SUPPLEMENT. 
17 
strange, and against the opinions of all that have before 
written.” 
That Norman, in the elucidation of his opinion, was standing 
on the threshold of truth, and breaking through the obscurity in 
which the variation of the needle was involved, must now be 
manifest. In the further exposition of this intricate and difficult 
subject, it may be proper to observe, that what we call the north 
magnetic pole is in fact a south pole, or, in other words, it is a 
magnetic pole, contrary to that pole of the needle, which is at¬ 
tracted by or directed towards the north pole of the earth, be¬ 
cause the magnetic attraction takes place only between poles of 
different denominations, and for the same reason, what w r e call 
the south magnetic pole of the earth, is, in fact, a north pole. 
It is likewise evident, that according to the position of these 
inagmetic poles, the compass needle will be differently affected, 
and from thence we are entitled to draw the following results:— 
If the magnetic poles of this earth had coincided vrith the 
true poles thereof, there could have been no declination or vari¬ 
ation of the mariner’s compass in any part of the world, that is, 
if the earth’s uniformity be magnetical; for in that case the 
needle, in pointing to the magnetic poles, must also have pointed 
to the true poles. This needle would, therefore, be necessarily 
directed along the course of the meridian, or, in other words, it 
would not have any declination either to the east or west 
thereof. 
If the magnetic poles were situated in the same meridian, and 
in opposite parallels upon that meridian which passes through 
the magnetic or true poles, from one of the magnetic to the 
other, and upon the opposite meridian all along, there could be 
no declination, for the reason mentioned in the former case, like¬ 
wise upon the equator there would be no declination ; for though, 
if one of the magnetic poles was only to act upon the needle, in 
passing along the equator to the distance of 90° in longitude 
east or west, the declination would increase; so that at 90° dis¬ 
tance from the line of no declination, it would be equal to the 
angle contained between the magnetic and the true poles, yet as 
the other magnetic pole in this case is always within the same 
31. 
c* 
