74 
FIFTH REPORT -1835. 
extremely well with the actual variation in the neighbourhood of 
Hudson’s Bay and Straits, and in the Southern Indian Ocean be¬ 
tween New Holland and the Cape of Good Hope ; that is to say, 
in places which are in the immediate vicinity of one or other of 
the poles of that axis. 2 nd, The variations computed from the 
weaker axis a b represent, hut not so perfectly as in the prece¬ 
ding case, the variations observed in the neighbourhood of its 
poles in South America and in Siberia. Hence we perceive, that 
in those localities where the force of each pole might be expected 
respectively to predominate, Euler’s lines of variation calculated 
for the axis of that pole accord with the phenomena. 3rd, The 
greater the distance that any point on the earth’s surface is from 
the poles of either axis, the less the observations are repre¬ 
sented by either system of lines taken separately. Thus, in the 
eastern hemisphere, we ought to have for the axis A B a line of 
25° west variation, passing through Northern Spain, Southern 
France, Germany, Prussia, Finland,and Russian Lapland; whilst 
from the weaker axis a h we should expect an easterly variation 
of from 6 ° to 7° in Spain, 10° in Finland, and 12 ° in Lapland. 
The combined influence of both axes should then produce a va¬ 
riation, in Spain, between the limits of 25° W. and 16° E.; in 
Finland, between 25° W. and 10 ° E.; and in Lapland, between 
25° W. and 12 ° E. Now the variation map of 1770 shows in 
Spain 20 ° W., in Finland 5° to 6 ° W., and in Lapland 0 . The 
nearer either pole of the axis a h is approached, the more the ob¬ 
served variation differs from that which, would be given by the 
axis AB, and approximates to that which is due to the axis ab. 
In the western hemisphere the line of no variation computed from 
a b passes south-west of the Californian Sea to the intersection 
of the meridian of 243 J E. with the latitude 15° f S., from whence 
its course is more southerly towards the pole a. In the map of 
the variation in 1770 , there is an obvious relation in the configu¬ 
ration of the lines of variation in the Pacific to this line of no 
variation due to the axis a b. Nowhere on the line is the actual 
variation in strict accordance with it, the nearest approach 
being 2 °E.; the difference is occasioned by the influence of the 
stronger pole A. To the westward of this line, if the axis ab 
acted alone, the variation would have been westerly, but the ef¬ 
fect of the stronger pole predominates as it is approached. Near 
New Zealand AB would give between 20 ° and 25° E., and ab 
15° W. : the map shows 15° E. At Behring’s Strait A B would 
give a somewhat greater easterly variation than is shown by the 
map of 1770 ; and here the neighbourhood of the weaker pole b 
draws the north pole of the needle to the westward. On a close 
and careful examination, it will be found a general rule, that the 
