How the Power dwells in the
_Loadstone_.
That a loadstone attracts loadstone, iron and other magnetical bodies, has
been shown above in the previous book, and also with what strength the
magnetick coition is ordered; but now we must inquire how that vigour is
disposed in a magnetick substance. And indeed an analogy must be inferred
from a large loadstone. Any magnetick substance joins itself with a
loadstone strongly, if the loadstone itself is strong; but more weakly,
when it is somewhat imperfect or has been weakened by some flaw. A
loadstone does not draw iron equally well with every part; or a magnetick
substance does not approach every part of a loadstone alike; because a
loadstone has its points, that is its true poles, in which an exceptional
virtue excels. Parts nearer the pole are {72} stronger, those far away more
weak, and yet in all the power is in a certain way equal. The poles of a
terrella are A, B; the æquinoctial is C, D. At A and B the alluring force
seems greatest.
[Illustration]
At C and D there is no force alluring magnetick ends to the body, for the
forces tend toward both poles. But direction is powerful on the æquator. At
C, D, the distances are equal from both poles; therefore iron which is at
C, D, when it is allured in contrary ways, does not adhære with constancy;
but it remains and is joined to the stone, if only it incline to the one or
other side. At E there is a greater power of alluring than at F, because E
is nearer the pole. This is not so because there is really greater virtue
residing at the pole, but since all the parts are united in the whole, they
direct their forces towards the pole. From the forces flowing from the
plane of the æquinoctial towards the pole, the power increases. A fixed
verticity exists at the pole, so long as the loadstone remains whole; if it
is divided or broken, the verticity obtains other * positions in the parts
into which it is divided. For the verticity always changes in consequence
of any change in the mass, and for this cause, if the terrella be divided
from A to B, so that there are two stones, the poles will not be A, B, in
the divided parts, but F, G, and H, I.
[Illustration] {73}
Although these stones now are in agreement with one another, so that F
would not seek H, yet if A was previously the boreal pole[163], F is now
boreal, and H also boreal; for the verticity is not changed (as Baptista
Porta incorrectly affirms in the fourth chapter of his seventh book);
since, though F and H do not agree, so that the one would incline to the
other, yet both turn to the same point of the horizon. If the hemisphere H
I be divided into two quadrants, the one pole takes up its position in H,
the other in I. The whole mass of the stone, as I have said, retains the
site of its vertex constant; and any part of the stone, before it was cut
out from the block[164], might have been the pole or vertex. But concerning
this more under _Direction_. It is important now to comprehend and to keep
firmly in mind that the vertices are strong on account of the force of the
whole, so that (the command being, as it were, divided by the æquinoctial)
all the forces on one side tend towards the north; but those of an opposite
way towards the south, so long as the parts are united, as in the following
demonstration.
[Illustration]
For so, by an infinite number of curves from every point of the equator
dividing the sphere into two equal parts, and from every point of the
surface from the æquator towards the North, and from the æquator towards
the Southern pole, the whole force tends asunder toward the poles. So the
verticity is from the æquinoctial {74} circle towards the pole in each
direction. Such is the power reposed in the undivided stone. From A vigour
is sent to B, from A, B, to C, from A, B, C, to D, and from them likewise
to E. In like manner from G to H, and so forth, as long as the whole is
united. But if a piece A B be cut out (although it is near the æquator),
yet it will be as strong in its magnetical actions as C D or D E, if torn
away from the whole in equal quantity. For no part excels in special worth
in the whole mass except by what is owing to the other adjoining parts by
which an absolute and perfect whole is attained.
_Diagram of Magnetic Vigour
transmitted from the plane of the Æquator
to the peripherery of the terella
or of the earth_
[Illustration]
{75} HEQ is a terrella, E a pole, M the centre, HMQ the æquinoctial plane.
From every point of the æquinoctial plane vigour extends to the periphery,
but by various methods; for from A the formal force is transmitted towards
C, F, N, E, and to every point from C up to E, the pole; but not towards B;
so neither from G towards C. The power of alluring is not strengthened in
the part FHG from that which is in GMFE, but FGH increases the force in the
eminence FE. So no force rises from the internal parts, from the lines
parallel to the Axis above those parallels, but always inwards from the
parallels to the pole. From every point of the plane of the equator force
proceeds to the pole E, but the point F has its powers only from GH, and N
from OH; but the pole E is strengthened from the whole plane HQ. Wherefore
in it the mighty power excels (just as in a palace); but in the
intermediate intervals (as in F) only so much force of alluring is exerted
as the portion HG of the plane can contribute.
* * * * *