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Mr. Christie's theory of the 
on the equator will be 150° west, or 210° east from the hottest 
point. On the northern side of the equator, we should there- 
fore have the north pole which is to the west of the place of 
heat, of greater intensity, and nearer to that place, than the 
south pole which is to the east of it ; but, supposing the 
hypothesis to be correct, the precise situations of these poles 
could only be determined from accurate observations of the 
diurnal variation of the needle. Different points in the 
earth’s equator becoming successively those of greatest heat, 
these poles would be carried round the axis of the earth, and 
would necessarily cause a deviation in the directions of the 
horizontal needle in different parts of its surface. We have 
then to consider, whether the deviations that would arise 
from magnetic poles, so circumstanced, correspond with the 
observed diurnal variations of the needle. 
With this view, I had proposed to compare the deviations 
of the needle, caused by the compound plate of bismuth and 
copper, with the diurnal changes in the needle, observed at 
different places, by adjusting the plate so that its plane should 
make with the horizon an angle equal to the complement of 
the latitude of the place of observation, and the axis about 
which it revolved an angle with the magnetic meridian equal 
to the variation at that place : the centre of the needle being 
then placed vertically over the centre of the plate, the poles 
in the plate would represent those which I have supposed to 
be developed on each side of the equator. I however found 
that at such a distance as the compass would here be placed 
from the plate, the deviations caused by it would not be of a 
magnitude to be determined with sufficient accuracy, with the 
small compass which I had employed. A pretty close approx- 
