On the Magnet, by William Gilbert

Chap. xiii. Why no other Body, excepting a magnetick, is imbued with verticity by being rubbed on a loadstone; and why no body is able to instil and excite that virtue, unless it be a magnetick.

L igneous substances floating on water never by their own strength turn round toward the poles of the earth, save by chance. So wires of gold, silver, brass, tin, lead, or glass, pushed through corks and floating, have no sure direction; and for this reason they do not show poles or points of variation when rubbed with a loadstone. For those things which do not of themselves incline toward the poles and obey the earth are also not ruled by the touch of a loadstone; for the magnetick vigour has no entrance into their inward parts; neither is the magnetick form received by them, nor are their forms magnetically excited; nor, if it did enter, would it effect anything, because in those bodies (mixed up with various kinds of efflorescent humours and forms, corrupted from the original property of the earth) there are no primary qualities. But those prime qualities of iron are excited by the juxtaposition of a loadstone, just as brute animals or men, when they are awakened out of sleep, move and put forth their strength. Here one must marvel at a demonstrable error of B. Porta, who, while rightly opposing a very old falsehood about the diamond, in speaking of a power contrary to that of the loadstone, introduces another still worse opinion; that forsooth iron, when touched by a diamond, turns to the north. “If” (he says) “you rub a steel-Needle on a Diamond, and then put it in a Boat, or thrust it through a reed, or hang it up by a Thread, it will presently turn to the North, almost as well as if it had been touched with the Loadstone; but something more faintly. And, what is worth noting, the contrary part will turn the iron to the South: and when I had tried this in many steel-Needles, and put them all into the Water, I found, that they all stood equi-distant, pointing to the North.” This indeed would be contrary to our magnetick rules. For this reason we made an experiment with seventy excellent diamonds, in the presence of many witnesses, on a large number of spikes and wires, with the most careful precautions, floating (thrust, of course, through their corks) on the surface of water; never, however, could we observe this. He was deceived by the verticity acquired from the earth (as stated above) in the spike or wire of iron itself, and the iron itself turned aside to its own definite pole; and he, being ignorant of this, thought it was done by the diamond. But let the investigators of natural phenomena take heed that they are not the more deceived by their own badly observed experiments, and disturb the commonwealth of letters with their errors and stupidities. Diamond is sometimes designated by the name of Sideritis, not because it is made of iron or because it draws iron, but on account of its lustre, resembling flashing steel; with such a lustre do the choicest pieces of diamond shine; hence by very many writers many qualities are imputed to diamond which really belong to siderite loadstone.


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