Page:On the Magnet - Gilbert (1900 translation of 1600 work).djvu/127



HE extraordinary magnetick virtue of the earth is remarkably demonstrated by the subtility of the following magnetical experiment. Let there be given a terrella of no contemptible power, or a long loadstone with equal cones as polar extremities; but in any other shape which is not exactly round error is easy, and the experiment difficult. In the Northern regions, raise the true North pole of the terrella above the horizon straight toward the zenith; it is demonstrable that it raises up a larger iron spike on its North pole, than the South pole of the same terrella is able to raise, when turned in the same way toward the highest point of the sky. The same thing is shown by a small terrella placed in the same way above a larger.



Let a b be the earth or a somewhat large terrella, also a b a smaller terrella. There is set up above the Northern pole of the smaller terrella a spike larger than the pole b of the smaller terrella can raise, if it is turned round to the higher parts. And the pole a of the