SUPPLEMENT* 
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and 1666 at Paris, a west declination began, and has ever since 
increased gradually, though not uniformly or in direct propor¬ 
tion of the times; for such is the nature of magnetic declination, 
that, like the apparent motion of the planets, sometimes it is 
faster, sometimes slower, at other times it is stationary, analo¬ 
gous also to the elongations of the inferior planets, at one time 
it is to the east, and at another time to the west, alternately. 
We may farther observe, that the declination lines of the same 
name have always respectively passed London, some years before 
the same lines arrived at Paris; and the like observations have 
been made in other parts of the northern hemisphere, that is, in 
this hemisphere, the Halleyan lines have regularly passed those 
places first which lay more westerly, and so in order those which 
lay more to the eastward. 
From the latter end of the sixteenth century there was an 
eastern declination over most parts of Europe, while on the coasts 
of North America a west declination prevailed; the lines of no de¬ 
clination being then situated about the Azores. This line of no 
declination has ever since moved gradually eastward, the lines 
of east declination receding before it, while the lines of the 
west declination have gradually followed it. 
In the southern hemisphere, however, it is quite otherwise; 
for about the latter end of the sixteenth century, a line of no de¬ 
clination passed near to the Cape of Good Hope, upon the east 
side of which there was west declination, and upon the west 
side thereof east declination; each of which declinations, in 
going eastward or westward, gradually increased to a certain 
degree, and then in the same manner decreased to nothing, 
somewhere to the eastward of Java. 
In the year 1775 the declination in the Pacific Ocean was sup¬ 
posed to be easterly over the greater part of that immense sur¬ 
face of water. The line of no declination, which was then situ¬ 
ated a little to the eastward of the Cape of Good Hope, has ever 
since been moving to the westward, and the lines of east declination 
have gradually receded before it, while those of the west decli¬ 
nation have followed it with a proportional pace ; so that at the 
Cape of Good Hope there was a considerable west declination 
