64 
FIFTH REPORT — 1835 . 
movement of the line of no variation, advanced towards the east, 
until they joined the corresponding lines of westerly variation, 
moving in the opposite direction in Africa and the Indian seas ; 
and the two united have appeared as cont inuous lines, from that 
time to the present. 
If the map of 1700 be placed over that of 1600, and the 
points be marked in the latter in which the variation is the same 
in both, and a line be drawn connecting those points, two such 
lines will appear, one from Labrador across the Atlantic and the 
Brazilian continent, the other through the Persian and Arabian 
Gulfs and Madagascar. 
The first of these lines is intersected near the middle by the 
line of no variation in 1600 : the part north of the intersection 
is comprised within the region of westerly variation, and the 
part south of it within the region of easterly variation. On the 
east of the northern part the westerly variation increased be¬ 
tween 1600 and 1700, and diminished on the west of it. On 
the east side of the southern part the easterly variation dimi¬ 
nished, and increased on the west side. On the whole eastern 
side of the line of no change the magnetic direction became 
more westerly; the westerly variation increasing, and the 
easterly diminishing; whilst the converse held good on the 
western side. Hence it follows that the lines of westerly varia¬ 
tion in the Atlantic turned on the points of their intersection 
with the line of no change, as on pivots, their motion being 
that usually termed u with the sun,”, causing the westerly va¬ 
riations to impinge successively on the North-west of Europe, 
and to advance progressively towards the south-east. It was 
thus that the line of no variation which was observed in London 
in 1657 did not reach Paris until 1666, nine years subsequent. 
Ascending from particular to general conclusions, it may be 
stated as a general fact, that in the northern hemisphere the 
lines of variation collectively have an eastward motion, and in 
the southern hemisphere a westward motion. 
In the map of 1700 the lines of no change between 1700 and 
1756 are marked in a similar manner. In comparing the At¬ 
lantic line with its corresponding one, between 1600 and 1700 , 
very little difference is perceived. The Indian line forms a 
pretty regular curve, from the Arabian Gulf and Madagascar 
to the 45th parallel of south latitude, and thence to the Straits 
of Sunda, and to China. At all places lying within the bend of 
this curve, the westerly variation diminished between 1700 and 
1756, and increased in those lying outside of it. 
In comparing the maps of 1787 and 1800, the westerly varia¬ 
tion, which in 1787 occupied the eastern part of Asia, is found 
