Chap. xxxi. On Long and Round Stones.
ieces of iron join more firmly with a long stone than with a round one, provided that the pole of the stone is at the extremity and end of its length; because, forsooth, in the case of a long stone, a magnetick is directed at the end straight towards the body in which the virtue proceeds in straighter lines and through the longer diameter. But a somewhat long stone has but little power on the side, much less indeed than a round one. It is demonstrable180, indeed, that at A and B the coition is stronger in a round stone than at C and D, at like distances from the pole.
180 Page 99, line 10. Page 99, line 11. Manifestum est.— In this, as in many other passages, Gilbert uses this expression in the sense that it is demonstrable rather than meaning that it is obvious: for the fact here described is one that is not at all self-evident, but one which would become plain when the experiment had been tried. For other instances of this use of manifestum see pages 144, line 20; 158, line 19; 162, line 10.
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