by William Gilbert

“ 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. ”

“ Magneticks acquire strength through magneticks, if they are properly placed according to their nature, in near neighbourhood and within the orbe of virtue. Wherefore when a terrella is placed on the earth or on a terrella, so that its Southern pole is turned round toward the Northern pole, its Northern pole, however, turned away from the Northern pole, the influence and strength of its poles are increased. And so the Northern pole of a terrella in such a position lifts up a larger spike than the Southern pole, if the Southern pole is turned away. ”