On the Rubbing of a piece of Iron on a Loadstone
in places midway between the poles, and upon
_the æquinoctial of a terrella_.
Select a piece of iron wire of three digits length, not touched by a
loadstone (but it will be better if its acquired verticity be rather weak
or have been damaged in some way); touch it and rub it on the æquator of a
terrella, exactly on the æquinoctial line in the direction of its length,
on the one end, or the ends only, or in all its parts; place the wire
touched in this * way on water in a cork fitted for it; it will swim about
doubtfully on the waves without any acquired verticity, and the verticity
previously implanted will be disturbed. If, however, it float by chance
toward the poles, it will be checked a little by the poles of the earth,
and will at length by the influence of the earth be indued with verticity.
* * * * *
{139} CHAP. XII.
In what way Verticity exists in any Iron that has
_been smelted though not excited by a lodestone_.
[Illustration]
Having thus far[211] demonstrated natural and inborn causes and powers
acquired by means of the stone, we will now examine the causes of magnetick
virtues in smelted iron that has not been excited by a stone. Loadstone and
iron furnish and exhibit to us wonderful subtilities. It has been
repeatedly shown above that iron not excited by a stone turns north and
south; further that it has verticity, that is, special and peculiar polar
distinctions, just as a loadstone, or iron which has been rubbed upon a
loadstone. This indeed seemed to us at first wonderful and incredible; the
metal of iron from the mine is smelted in the furnace; it runs out of the
furnace, and hardens into a great mass; this mass is divided in great
worksteads, and is drawn into iron bars, from which smiths again construct
many instruments and necessary pieces of iron-work. Thus the same mass is
variously worked up and transformed into very many similitudes. What is it,
then, which {140} preserves its verticity, and whence is it derived? So
take this first from the above[212] smithy. Let the blacksmith beat out
upon his anvil a glowing mass of iron of two or three ounces weight into an
iron spike of the length of a span of nine inches. Let the smith be
standing with his face to the north, his back to the south, so that * the
hot iron on being struck has a motion of extension to the north; and let
him so complete his work with one or two heatings of the iron (if that be
required); let him always, however, whilst he is striking the iron, direct
and beat out the same point of it toward the north, and let him lay down
that end toward the north. Let him in this way complete two, three, or more
pieces of iron, nay, a hundred or four hundred; it is demonstrable that all
those which are thus beaten out toward the north, and so placed whilst they
are cooling, turn round on their centres; and floating pieces of iron
(being transfixed, of course, through suitable corks) make a motion in the
water, the determined end being toward the north. In the same way also
pieces of iron acquire verticity from their direction whilst they are being
beaten out and hammered or drawn out, * as iron wires are accustomed to do
toward some point of the horizon between east and south or between south
and west, or in the opposite direction. Those, however, which are pointed
or drawn out rather toward the eastern or western point, conceive * hardly
any verticity or a very undecided one. That verticity is especially
acquired by being beaten out. But a somewhat inferior iron ore, in which no
magnetick powers are apparent, if put in a * fire (its position being
observed to be toward the poles of the world or of the earth) and heated
for eight or ten hours, then cooled away from the fire, in the same
position towards the poles, acquires a verticity in accordance with the
position of its heating and cooling. Let a rod of cast iron be heated
red-hot in a strong fire, in which it lies * meridionally (that is, along
the path of a meridian circle), and let be removed from the fire and
cooled, and let it return to its former temperature, remaining in the same
position as before; then from this it will turn out that, if the same ends
have been turned to the same poles of the earth, it will acquire verticity,
and the end which looked toward the North on water with a cork before the
heating, if it have been placed during the heating and cooling toward the
fourth, now turns round to the south. But if perchance sometimes the
rotation have been doubtful and somewhat feeble, let it be placed again in
the fire, and when it is taken out at a red heat, let it be perfectly
cooled toward the pole from which we desire the verticity, and the
verticity will be acquired. Let the same rod be heated * in the contrary
position, and let it be placed so at a red heat it is cool; for it is from
its position in cooling (by the operation of the verticity of the earth)
that verticity is put into the iron, and it turns round to parts contrary
to its former verticity. So {141} the end which formerly looked toward the
north now turns to the south. In accordance with these reasonings and in
these ways the boreal pole of the earth gives to the end of a piece of iron
turned toward it a southern verticity, and that end is attracted by that
pole. * And here it must be observed that this happens to iron not only
when it is cooled in the plane of the horizon, but also at any angle to it
almost up to the perpendicular toward the centre of the earth. So the
heated iron conceives vigour and verticity from the earth more quickly in
the course of its return to its normal state, and in its recovery, as it
were (in the course of which it is transformed), than by its mere position
alone. This is effected better and more * perfectly in winter and in colder
air, when the metal returns more certainly to its natural temperature, than
in summer and in warm regions. Let us see also what position alone and a
direction toward the poles of the earth can effect by itself without fire
and heat. Iron rods which have been placed and fixed for a long time,
twenty * or more years, from south to north (as they not infrequently are
fixed in buildings and across windows), those rods, I say, by that long
lapse of time acquire verticity and turn round, whether hanging in the air,
or floating (being placed on cork), to the pole toward which they were
pointing, and magnetically attract and repel a balanced iron magnetick; for
the long continued position of the body toward the poles is of much avail.
This fact (although conspicuous by manifest experiments) is confirmed by an
incident related in an Italian letter[213] at the end of a book of Maestro
Filippo Costa, of Mantua, _Sopra le Compositioni degli Antidoti_ written in
Italian, which translated runs thus: "A druggist of Mantua showed me a
piece of iron entirely changed into a magnet, drawing another piece of iron
in such a way that it could be compared with a loadstone. Now this piece of
iron, when it had for a long time held up a brick ornament on the top of
the tower of the church of St. Augustine at Rimini, had been at length bent
by the force of the winds, and remained so for a period of ten years. When
the monks wished to bend it back to its former shape, and had handed it
over to a blacksmith, a surgeon named Maestro Giulio Caesare discovered
that it was like a magnet and attracted iron." This was caused by the
turning of its extremities toward the poles for so long a time. And so what
has been laid down before about change of verticity should be borne in
mind; how in fact the poles of iron spikes are altered, when a loadstone is
placed against them only with its pole and points toward them, even at a
rather long distance. Clearly it is in the same way that that large magnet
also (to wit, the earth itself) affects a piece of iron and changes its
verticity. For, although the iron may not touch the pole of the earth, nor
any magnetick part of the earth, yet verticity is acquired and changed; not
because the poles of the earth and the point itself which is 39° distant
{142} from our city of London, changes the verticity at a distance of so
many miles; but because the whole magnetick earth, that which projects to a
considerable height, and to which the iron is near, and that which is
situated between us and the pole, and the vigour existing within the orbe
of its magnetick virtue (the nature of the whole conspiring thereto),
produces the verticity. For the magnetick effluence of the earth rules
everywhere within the orbe of its virtue, and transforms bodies; but those
things which are more similar to it, and specially connected with it by
nature, it rules and controls; as loadstone and iron. Wherefore in very
many matters of business and actions it is clearly not superstitious and
idle to observe the positions and conditions of lands, the points of the
horizon and the places of the stars. For as when a babe is brought forth
into the light from its mother's womb, and acquires respiration and certain
animal activities, then the planets and celestial bodies[214], according to
their position in the universe, and according to that configuration which
they have with regard to the horizon and the earth, instil peculiar and
individual qualities into the newly born; so that piece of iron, whilst it
is being formed and lengthened out, is affected by the common cause (to
wit, the earth); whilst it is returning also from its heated condition to
its former temperature, it is imbued with a special verticity in accord
with its position. Rather long pieces of iron sometimes have the same
verticity * at each end; wherefore they have motions which are less certain
and well ordered on account of their length and of the aforesaid processes,
exactly as when an iron wire four feet long is rubbed at each end upon the
same pole of a loadstone.
* * * * *