on long and round stones.

p 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.