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.
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.