SUPPLEMENT. 
27 
moving before it, while the lines of west variation followed it 
with a proportional pace. These lines first passed the Azores or 
Western Islands, then the meridian of London, and, after a cer¬ 
tain number of years still later, they passed the meridian of Paris. 
But in the southern hemisphere there was another line of no va¬ 
riation, which had east variation on its western, and west vari¬ 
ation on its eastern side ; the lines of east variation moving be¬ 
fore it, while those of the west variation followed it. This line 
of no variation first passed the Cape des Aiguilles, and then the 
Cape of Good Hope, the lines of 5°, 10°, 15°, and 20° west vari¬ 
ation following it, the same as was the case in the northern he¬ 
misphere, but in a contrary direction. 
Jt was originally the hypothesis of Dr. Knight, that the mag¬ 
netic poles were at first opposite to each other ; but, according 
to the doctrine of Mr. Canton, they would not long have con¬ 
tinued so, for, from the intense heat of the sun in the torrid zone, 
according to the principles already explained, the north pole 
must have soon retired to the north-eastward, and the south pole 
to the south-eastward. It is also curious to observe, that on ac¬ 
count of the southern hemisphere being colder upon the whole 
than the northern hemisphere, the magnetic poles would have 
moved with unequal pace ; that is, the north magnetic pole 
would pave moved further in any given time to the north-east 
than the south magnetic pole would have moved to the south¬ 
ward ; and according to the opinion of the most ingenious authors 
on this subject, it is generally allowed that at this time the north 
magnetic pole is considerably nearer to the north pole of the 
earth, than the south magnetic pole is to the south pole of the 
earth. 
We shall now proceed to give the memoir of Commander Ross, 
as it was delivered by him to the Royal Society, reserving to 
ourselves the opportunity of making those strictures, which the 
subject may require. 
