It Is Very Plain, From These
Observations, That The Position Laid Down By Dr. Halley, That The
Motion Of The
Needle is not governed by the poles of the world, but
by other poles, which move round them, is highly
Probable, for
otherwise it is not easy to understand how the needle came to have,
as our author affirms it had, a variation of near 27 degrees to the
west, in the latitude of 45 degrees 47 minutes, and then gradually
decreasing till it had no variation at all; after which it turned
east, in the latitude of 42 degrees 37 minutes, and so continued
increasing its variation eastwardly to this time.
CHAPTER VIII: OBSERVATIONS ON, AND EXPLANATION OF, THE VARIATION OF
THE COMPASS.
On the 16th we were in the latitude of 26 degrees 29 minutes south,
and in the longitude of 199 degrees 32 minutes, the variation of the
needle being 8 degrees. Here we are to observe that the eastern
variation decreases, which is likewise very agreeable to Doctor
Halley's hypothesis; which, in few words, is this: that a certain
large solid body contained within, and every way separated from the
earth (as having its own proper motion), and being included like a
kernel in its shell, revolves circularly from east to west, as the
exterior earth revolves the contrary way in the diurnal motion,
whence it is easy to explain the position of the four magnetical
poles which he attributes to the earth, by allowing two to the
nucleus, and two to the exterior earth.
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