How Iron acquires Verticity through
a Loadstone, and how that verticity
_is lost and changed_.
Friction between an oblong piece of iron and a loadstone imparts to the
former magnetick virtues, which are not corporeal nor inherent and
persistent in any body, as we showed in the discussion on coition. It is
plain that the iron, when it has been rubbed hard with one end and applied
to the stone for a pretty long time, receives no stony nature, acquires no
weight; for if, before the iron is touched by the stone, you weigh * it in
a small and very exact goldsmith's balance, you will see after the rubbing
that it has exactly the same weight, neither diminished nor increased. But
if you wipe the iron with cloths after it has been touched, or wash it in
water, or scour it with sand or on a grindstone, still it in nowise lays
aside its acquired strength. For the force is spread through the whole body
and conceived in the inmost parts, and cannot in any way be washed or wiped
away. Let an experiment then be made in fire, that untamed tyrant of
nature. Take a piece of iron of the length of a palm and the thickness of a
goosequill pen; let this iron be passed through a suitable round cork and
placed on the surface of water, and observe the end which turns to the
north; rub this particular end with the true southern end of a loadstone;
the iron so rubbed turns toward the south. Remove the cork, and place the
end * which was excited in the fire until the iron is just red-hot; when it
is cooled, it will retain the strength of the loadstone and the verticity,
though it will not be so prompt, whether because the force of the fire had
not yet continued long enough to overcome all its {124} strength, or
because the whole iron was not heated to redness, for the virtue is
diffused through the whole. Remove the cork a second time, and putting the
whole iron in the fire, blow the fire with the bellows, so that it may be
all aglow, and let it remain a little longer time red-hot; when cooled (so,
however, that, whilst it is cooling, it does not rest in one position),
place it again on the water with the cork, and you will see that it has
lost the verticity * which it had acquired from the stone. From these
experiments it is clear how difficult it is for the property of polarity
implanted by the loadstone to be destroyed. But if a small loadstone had
remained as long in the same fire, it would have lost its strength. Iron,
because it does not so easily perish, and is not so easily burnt up as very
many loadstones, retains its strength more stably, and when it is lost can
recover it again from a loadstone; but a loadstone when burnt does not
revive. But now that iron, which has * been deprived of its magnetick form,
moves in a different way from any other piece of iron, for it has lost its
polar nature; and whereas before the touch of the loadstone it may have had
a motion toward the north, and after contact toward the south; now it turns
to no definite and particular point; but afterwards, very slowly and after
* a long time, it begins to turn in a doubtful fashion toward the poles of
the earth (having acquired some power from the earth). I have said that the
cause of direction was twofold, one implanted in the stone and iron, but
the other in the earth, implanted by the disponent virtue; and for that
reason (the distinction of poles and the verticity in the iron having now
been destroyed) a slow and weak directive power is acquired anew from the
verticity of the earth. We may see, therefore, with what difficulty and
only by the application of hot fires and by long ignition of the iron
heated to softness, the imparted magnetick virtue is eradicated. When this
ignition has overcome the acquired polarity, and it has been now completely
subdued and not awakened again, that iron is left unsettled and utterly
incapable of direction. But we must further inquire how iron remains
affected by verticity. It is manifest that it strongly affects and changes
the nature of the iron, because the presence of a loadstone attracts the
iron to itself with an altogether wonderful readiness. Nor is it only the
part that is rubbed, but on account of the rubbing (on one end only) the
whole iron is affected together, and gains by it a permanent though an
unequal power. This is demonstrated as follows. Rub an iron wire on the end
so * that it is excited, and it will turn towards the north; afterward cut
off some portion of it; you will see that it still turns toward the north
(as before), but more feebly. For it must be understood that the loadstone
excites a steady verticity in the whole iron (if the rod be not too long)
more vigorous throughout the whole mass in a shorter bar, and as long as
the iron remains touching the loadstone a little {125} stronger. But when
the iron is separated from contact with it, then it becomes much weaker,
especially in the end that was not touched. Just as a long rod, one end of
which is placed in the fire and heated, grows exceedingly hot at that end,
less so in the parts adjoining and in the middle, whilst at the other end
it can be held in the hand, and that end is only warm; so the magnetical
vigour diminishes from the excited end to the other end; but it is present
there instantly, and does not enter after an interval of time nor
successively, as the heat in the iron; for as soon as a piece of iron has
been touched by a loadstone it is excited throughout its whole length. For
the sake of experiment, let there be a rod of iron 4 or * 5 digits long,
untouched by a loadstone; as soon as you touch one end only with a
loadstone, the opposite end immediately, or in the twinkling of an eye, by
the power that it has conceived, repels or attracts a versorium, if it be
applied to it ever so quickly.
* * * * *