CHAP. III.
How Iron acquires Verticity through
a Loadstone, and how that verticity
is lost and changed.
riction 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 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 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.