The Sun.
London, England, 1856-03-10 00:00:00

Vice-President, in the Chair.
MR. FARADAY, D.C.L., F.R.S., ON CERTAIN
MAGNETIC ACTIONS AND AFFECTIONS.
All bodies subject to magnetic induction, when placed
iu the ordinary magnetic field between the poles of a mag-
net, are affected ; paramagnetic bodies tend to pass
bodily from weaker to stronger places of force, and dia-
magnetic bodies from stronger to weaker places of force.
If the bodies are elongated, then those that are para-
magnetic set along the lines of force, and those that are
diamagnetic across them : but if these bodies have a
spherical form, are amorphous, and are perfectly free from
magnetic charge, they have no tendency to set in a par-
ticular direction. Nevertheless, there are bodies of both
classes, which being crystalline, have the power of set-
ting when a single crystal is wrought into the form of a
sphere, and these are called mane-crystals ; t&ir num-
ber is increasing continually ; carbonate of lime, bismuth,
tourmaline, &c., are of this nature. Bodies which, being
magnetic, set, because they are elongated, are greatly in-
fluenced in the force of the set by the nature of the me-
dium surrounding them, and to such an extent that they
not merely vary in their force from the maximum to
nothing, but will often set axially in ono medium, and
equatorially in another. Yet the Fame bodies, if league-
crystallic and formed into spheres, though they set well
in the magnetic field, will set with the same force what-
ever the change in the media about them, and are perfectly
freed from the influence of the latter. Thu% if a crystal
of bismuth formed into a sphere, or a vertical cylinder,
has, when suspended, its magne-crystallic axis horizontal,
and if the various media about it, from saturated solu-
tion of sulphate of iron up to phosphorus, through air,
water, alcohol, oil, be changed one for another, no alte-
ration in the amount of torsion force required to displace
the magne-crystal will occur, provided the force of the
magnet be constant, notwithstanding that the list of
media includes highly paramagnetic and diamagnetic
bodies ; and in such cases the measurement of the power
of set is relieved from a multitude of interfering cir-
cumstances existing in other cases, and that power which
is dependent upon the internal structure and condition
of the substance is proved to be, at the same tempera-
ture, always the same.
A consequence of inagne-crystallic structure is that the
same body is more paramagnetic, or more diamagnetic
in one direction than in another ; and, therefore, it fol-
lows that though such a crystal may have no variation
in set-force, produced by change of the surrounding me-
dium, it rimy have a variation produced in the absolute
force of attraction or repulsion ; even up to the I»iet of
being attracted in one position and repelled in another,
though no change in form, or in the surrounding me-
dium, or in the force of the magnet, or in the nature of
the body itself, be made; hut simply a change in the di.
rection of the structure. This was shown by a crystal
of the red forro-prussiate of potassa, which, being coated
carefully with wax, was suspended from the arm of a
tot sion balance, so that it dipped into a solution of preto-
sulphate of iron occupying the magnetic field.* When
the magne-cryetallic axis was parallel to the lines of force
the crystal was attracted by the magnetic pole, when it
was perpendicular to the lines of force the crystal was
repelled ; acting like a paramagnetic and diamagnetic in
turns. No magne•crystal has yet been found having
such a relation to a sacuuin, or t) carbonic acid (its meg-
netic equivalent) ; calcareous spar is nearly coincident
with such a medium, and shows different degrees of force
in the two directions, but is always a little on the diamag-
netic side. Calcareous spar having a trace of iron lots been
found very nearly up to the desired point; on the para-
magnetic side ; and as these preserve the full magne-crys-
trdlic relation of the two directions, there is no reason to
suppose that a crystal may not be found which may not
be paramagnetic in one direction, and diamagnetic in
another, in respect of space as zero.
There is every reason to beiieve that the general mae-
netic relations of a magne-crystal are the same with
those of the same substance in the amorphous state, and
that the circumstances which influence one influence the
other to the same degree. la that case, the magnetic
affections of a body might be ascertained by the exami-
nation of the magne-crystallic affections ; thus the effect
of heat upon bismuth, tourmaline, &c., might be exa-
mined by the set of the crystals, and with so much the
greater advantage that short globular forms could be
used, perfectly free from the magnetic influence of the
surrounding media required as temperature baths, and
requiring no displacement of these media with the mo-
tion of the crystal. So crystals et bismuth, tourmaline,
carbonate of iron, and other bodies, were suspended in
baths of oil, water, &e,, the temperature gradually raised
and lowered, and the torsion force of the set for each
force of 200 at 20 deg. F. was reduced to a force of 70
at 300 deg., and the diminution of force appeared to be
nearly equal in all parts of the scale for an equal number
of degrees. A piece of amorphous bismuth, compressed
in one direction, gave nearly the same amount and de-
gree of change for the same alteration of temperaterc ;
leading us to the persuasion that the whole magnetic
force of bismuth as a diamagnetic body would suffer
little change. A crystal of tourmaline, which at 0 deg.
had a setting force of 540, when raised to 300 degrees,
had a setting force of only 270 ; the loss of force
was progressive, being greater at lower than at high
temperatures ; for a change from 0 deg. to 30 deg. caused
aloes of force equal to 50, whilst a change from 270 deg.
to 300 deg. caused a loos of only 20. Carbonate of iren
suffered a like change ; at 0 deg. the force was 1,140, at
300 deg. it was only 415 ; at the lower temperature the
loss for 30 deg. was 120 loss of force, at the upper it
was only 34,
In all these and in many other cases, both with para-
magnetic and diamagnetic bodies, the magne-crpstallic
differences diminished with the elevation of tempera-
ture ; and therefore it may be considered probable that
the actual magnetic force changed in the same direction.
But on extending the results to iron, nickel, and cobalt,
employing these metals as very small prisms associated
with copper cubes to give them weight, it was found that
another result occurred. Iron, whether at the tempera-
`Aire of 30 deg. or 300 deg., or any intermediate degree,

underwent no change of force ; it remained at 300, which
was the expression for the piece employed under the
circumstances. We know that at higher temperatures it
loses power, and that at a bright red it is almost desti-
tut3 of inductive magnetic force. A piece of nickel,
which at 95 deg. bad a setting power of 300, when raised
to 285 deg., had a power of only 220, so that it had
lost a thirtieth part of its force; at the heat of
boiling oil it is known to lose nearly all its force, being
unable then to affect a magnetic needle. Cobalt, on the
other band, requires a far higher temperature than iron
to remove its magnetic character, a heat near that of
melting copper being necessary. As to lower tempera-
tures it was found that au elevation from 70 deg. to
300 deg. caused an absolute increase of the magnetic force
from 293 to 333. It is evident, therefore, that there is a
certain temperature, or range of temperature above 300
deg., at which the magnetic force of cobalt is a maxi-
mum ; and that elevation above, or depression below,
that temperature cans, s a diminution of the force. The
case is probably the same for iron, its maximum magne-
tic force occurring at temperatures between 0 dec. and
300 deg. If nickel is subjected to the same cenoitions
of a maximum, then that state must come on at tempera.
tares below 0 deg.; and it may be
further remarked,
that as the maximum conditions occur in the following
order for ascending temperatures, nickel, iron, cob Lit,
such also is the same order for the temperatures at
which they lose their high and distinctive magnetic place
among metals.

* 2 volumes of saturated solutiou, at 65 deg,
1. volume of water,