22 
SUPPLEMENT. 
North America, enters the Atlantic Ocean to the northward of 
Charleston, and so proceeds to the south pole. Upon the west 
side of this line there is east declination, and upon the east side 
thereof west declination, which last gradually increases as we 
proceed to the eastward, and till we get beyond the Cape of 
Good Hope, or midway between the Atlantic and the East India 
line of no declination, where it amounts to 31° about the latitude 
of 48° south, and then it regularly decreases to the East India 
line of no declination. 
Again, as we proceed to the eastward of that line of no decli¬ 
nation, the east declination increases rapidly till you get to the 
eastward of New Zealand, where it is upwards of 13° even in that 
latitude ; but from thence as we proceed eastward for about 40° 
in longitude, this declination appears to decrease; and again it 
increases till we are to the eastward of Cape Horn, where, in 
the latitude of 51° south, it amounts to 21° 28', and then gradu- 
allydecreases to the Atlantic line of no declination aforesaid. 
Upon the whole, it would appear that these observations agree 
pretty nearly with those already advanced, with the exception of 
that decreasing east declination to the eastward of New Zealand. 
But admitting that the vast body of water in the great Pacific 
Ocean, which cannot have any magnetic properties, should not 
have any effect in producing this irregularity, yet we are not to 
expect even that the solid parts of this globe can be so uniformly 
magnetical throughout as to answer entirely with calculation in 
every part thereof. 
The magnetic needle not only declines or varies from the true 
north, differently in different parts of the earth at one time, but 
likewise in the same place this declination is different at differ¬ 
ent times. We will therefore call it, by way of distinction, the 
variation of the magnetic needle. 
At London and Paris, where the most accurate observations 
have been made towards the latter end of the sixteenth century, 
and we cannot pretend to much earlier observations, there were 
between 11° and 12° of east declination, which gradually de¬ 
creased ; so that, in less than a hundred years afterwards, there 
was no declination at all in those places. From 1657 at London, 
