S62 Mr. Christie on the magnetism of 
From these observations it appears, that when the centre 
of the plate was in the pole of the magnetic sphere, its plane 
being parallel to the equator, the position of the needle, for 
any situation of the several points of the plate, was the same 
whether they were brought into that situation by the plate 
revolving from east through south to west, or from west 
through south to east ; that is, that the deviation due to rotation 
was nothing : 
That the deviation due to rotation increased from this point 
towards the equator, where it was the greatest : 
And that the horizontal needle was affected by the rotation 
of the plate, not according to the situation of the centre of the 
plate as regarded the poles and equator of the horizontal 
needle, but as regarded the poles and equator of an ima- 
ginary dipping needle passing through the centre of the 
horizontal needle. 
This last is not so evident, from the circumstance of the 
deviation being nothing when the centre of the plate was in 
the pole of the dipping needle, and a maximum when in the 
equator, as from its being very nearly equal at equal distances 
on each side of the pole, and also of the equator, that is, at 
very unequal distances from the axis of the horizontal 
needle ; and from the deviations at equal distances from the 
axis of the horizontal needle being very unequal. For if we 
compare the deviation due to rotation in lat. 70® 30' S, long. 90°, 
with that in lat. 70° 30'S, long. 270®, the difference is only 
1' ; in the first case, the centre of the plate was at the dis- 
tance of 90® from the axis of the horizontal needle, and its 
plane parallel to it ; and in the other at the distance of 31®, 
and its plane making an angle of 39° with this axis. Again, 
