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.

And, as the two former perpetually alter the situation by their circular motion, their virtue, compared with the exterior poles, must be different at different times, and consequently the variation of the needle will perpetually change.

The doctor attributes to the nucleus an European north pole and an American south one, on account of the variation of variations observed near these places, as being much greater than those found near the two other poles.

And he conjectures that these poles will finish their revolution in about seven hundred years, and after that time the same situation of the poles obtain again as at present, and, consequently, the variations will be the same again over all the globe; so that it requires several ages before this theory can be thoroughly adjusted.