Showing that Movements take place by the Magnetical
Vigour though solid bodies lie between; and on
_the interposition of iron plates_.
Float a piece of iron wire on the surface of water by transfixing it
through a suitable cork; or set a versatory piece of iron on a pin or in a
seaman's compass (a magnet being brought near or moved about underneath),
it is put into a state of motion; neither the water, nor the vessel, nor
the compass-box offering resistance in any way. Thick boards do not
obstruct[168], nor earthen vessels nor marble vases, nor the metals
themselves; nothing is so solid as to carry away or impede the forces
excepting an iron plate. Everything which is interposed (even though it is
very dense) does not carry away its influence or obstruct its path, or
indeed in any way hinder, diminish, or retard it. But all the force is not
suppressed by an iron plate, but it is in some measure diverted aside. For
when the vigour passes into the middle of an iron plate within the orbe of
the magnetick virtue or placed just {84} opposite the pole of the stone,
that virtue is scattered in very large measure towards its extremities; so
that the edges of a small round * plate of suitable size allure iron wires
on every side. This is also apparent in the case of a long iron wand,
which, when it has been touched by a magnet in the middle, has a like
verticity at either end. *
[Illustration]
B is a loadstone, C D a long rod magnetized in the middle A; E being the
Boreal pole; C is an Austral end or pole; in like manner also the end D is
another Austral pole. But observe here the exactness with which a versorium
touched by a pole, when a round plate is interposed, turns towards the same
pole in the same * way as before the interposition, only weaker; the plate
not standing in the way, because the vigour is diverted through the edges
of the small plate, and passes out of its straight course, but yet the
plate retains in the middle the same verticity, when it is in the
neighbourhood of that pole, and close to it; wherefore the versorium tends
towards the plate, having been touched by the same pole. If a loadstone is
rather weak, a versorium hardly turns when a plate is put in between; for
the vigour of the rather weak loadstone, being diffused through the
extremities, passes less through the * middle. But if the plate has been
touched in this way by a pole in the middle and has been removed from the
stone outside its orbe of virtue, then you will see the point of the same
versorium tend in the contrary direction and desert the centre of the small
plate, which formerly it desired; for outside the orbe of virtue it has an
opposite verticity, in the vicinity the same; for in the vicinity it is, as
it were, a part of the loadstone, and has the same pole.
[Illustration]
A is an iron plate near the pole, B a versorium which tends with its point
towards the centre of the small plate, which has been touched by the pole
of the loadstone C. But if the same small plate be {85} placed outside the
orbe of magnetick virtue, the point will not turn towards its centre, but
the cross E of the same versorium does. But an iron globe interposed (if it
is not too large) attracts the * point of the iron on the other side of the
stone. For the verticity of that side is the same as that of the adjoining
pole of the stone. And this turning of the cusp (that is, of the end
touched by that pole) as well as of the cross-end, at a greater distance,
takes place with an iron globe interposed, which would not happen at all if
* the space were empty, because the magnetick virtue is passed on and
continued through magnetick bodies.
[Illustration]
A is a terrella, B an iron globe; between the two bodies is F, a versorium
whose point has been excited by the pole C. In the other figure A is a
terrella, C its pole, B an iron globe; where the versorium tends towards C,
the pole of the terrella, through the iron globe. So a versorium placed
between a terrella and an iron globe vibrates more forcibly towards the
pole of the terrella; because the loadstone sends an instantaneous
verticity into the opposite globe. There is the same efficiency in the
earth, produced from the same cause. For if a revolvable needle is shut up
in a rather thick gold box (this metal indeed excels all others in density)
or a glass or stone box, nevertheless that magnetick needle has its forces
connected and united with the influences of the earth, and the iron will
turn freely and readily (unhindered by its prison) to its desired points,
North and South. * It even does this when shut up in iron caverns, if they
are sufficiently spacious. Whatever bodies are produced among us, or are
artificially forged from things which are produced, consist of matter of
the terrestrial globe; nor do those bodies hinder the prime forces of
nature which are derived from their primary form, nor can they resist them
except by contrary forms. But no forms of mixed bodies are inimical to the
primary implanted earth-nature, although some often do not agree[169] with
one another. But in the case of all those substances which have a material
cause for their inclining (as amber, {86} jet, sulphur), their action is
impeded by the interposition of a body (as paper, leaves, glass, or the
like) when that way is impeded and obstructed, so that that which
exhales[170] cannot reach the corpuscle to be allured. Terrestrial and
magnetick coition and motion, when corporeal impediments are interposed, is
demonstrated also by the efficiencies of other chief bodies due to their
primary form. The moon (more than all the stars) agrees with internal parts
of the earth on account of its nearness and similarity in form. The moon
produces the movements of the waters and the tides of the sea; twice it
fills up the shores and empties them whilst it moves from a certain
definite point in the sky back to the same point in a daily revolution.
This motion of the waters is incited and the seas rise and fall no less
when the moon is below the horizon and in the lowest part of the heavens,
than if it had been raised at a height above the horizon. So the whole mass
of the earth interposed[171] does not resist the action of the moon, when
it is below the earth; but the seas bordering on our shores, in certain
positions of the sky when it is below the horizon, are kept in motion, and
likewise stirred by its power (though they are not struck by its rays nor
illuminated by its light), rise, come up with great force, and recede. But
about the reason of the tides anon[172]; here let it suffice to have merely
touched the threshold of the question. In like manner nothing on the earth
can be hidden from the magnetick disposition of the earth or of the stone,
and all magnetical bodies are reduced to order by the dominant form of the
earth, and loadstone and iron show sympathy with a loadstone though solid
bodies be interposed.
* * * * *