CHAP. X.
On Mutation of Verticity and of Magnetick
Properties, or on alteration in the power
excited by a loadstone.
riction with a loadstone gives to a piece
of iron a verticity strong enough; not, however, so stable that the iron may not by being rubbed on the opposite part
(not only with a more powerful loadstone, but with the same) be changed and deprived of all its former verticity, and
indued with a new and opposite one. Take a piece of iron wire and rub each end of the wire equally with one and the same
pole of a loadstone, and let it be passed through a suitable cork and place it on water. Then truly one end of the wire
will be directed toward that pole of the earth toward which that end of the stone will not turn. But which end of the
iron wire will it be? That certainly which was rubbed last. Rub the other end of this again with the same pole, and
immediately * that end will turn itself
in the opposite direction. Again touch the former end of the iron wire only with the same pole of the loadstone as
before; and that210 end, having gained the command, immediately changes to the
contrary side. So you will be able to change the property of the iron frequently, and that end of the wire rules which
has been touched the last. Now then merely hold the boreal pole of the stone for some time near the boreal part of the
wire which was last touched, so that it does not touch, but so that it is removed from it by one, two, or even three
digits, if the stone have been pretty *
strong; and again it will change its property and will turn round to the contrary side; which will also happen (albeit
rather more feebly) even if the loadstone be removed to a distance of four digits. You will be able to do the same thing,
moreover, with both the austral and the boreal part of the stone in all these experiments. Verticity may likewise be
acquired and changed when thin plates of gold, * silver, and glass are interposed between the
stone and the end of the iron or iron wire, if the stone were rather strong, even if the intermediate lamina is not touched either by the iron or the stone. And these changes of verticity take
place in smelted iron. Indeed what the one pole of the stone implants and excites, the other disturbs and extinguishes,
and confers a new force. For it does not require a stronger loadstone to take away the weaker and sluggish virtue and to
implant the new one; nor is iron inebriated by the equal strength of loadstones, and made utterly uncertain and neutral,
as Baptista Porta teaches; but by one and the same loadstone, or by loadstones endowed with equal power and might, its
strength is, in accordance with magnetick rules, turned round and changed, excited, repaired, or disturbed. But a
loadstone itself, by being rubbed on another, whether a larger or a more powerful stone, is not disturbed from its own
property and verticity, nor does it turn round toward the opposite direction in its boat, or to the other pole opposite
to that to which it inclines by its own nature and implanted verticity. For strength which is innate and has been
implanted for a very long time abides more firmly, nor does it easily yield from its ancient holding; and that which has
grown for a long time is not all of a sudden brought to nothing, without the destruction of the substance containing it.
Nevertheless in a long interval of time a change * does take place; in one year, that is to say, or
two, or sometimes in a few months; doubtless when a weaker loadstone remains lying by a stronger one contrary to the
order of nature, namely, with the northern pole of one loadstone adjoined to the northern pole of another, or the
southern to the southern. For so the weaker strength gradually declines with the lapse of time.