MAGNETISM.
Magnetic Iron--Knowledge of, by the Ancients--Artificial
Magnets--Electro-Magnets--Electro-Magnetism--Magneto-
Electricity--Theories of Magnetism--The Magnetic Power of soft Iron
and Steel--Influence of Heat on Magnetism--Terrestrial
Magnetism--Declination of the Compass-needle--Variation of the
Earth’s Magnetism--Magnetic Poles--Hansteen’s Speculations--Monthly
and Diurnal Variation--Dip and Intensity--Thermo-Magnetism--Aurora
Borealis--Magnetic Storms--Magnetic conditions of
Matter--Diamagnetism, &c.
Agreeably with the view now generally received, that magnetism and
electricity are but modifications of one force, since they are found to
stand to each other in the relation of cause and effect, the separation
which is here adopted, of the consideration of their several phenomena,
may appear inappropriate. The importance, however, of all that is
connected with magnetism, and the very decided difference which is
presented by true magnetic action, and that of frictional or chemical
electricity, is so great that it has been thought advantageous to adopt
the present arrangement in reviewing the influence of terrestrial
magnetism with which science has made us acquainted.
From a very early period a peculiar attractive force has been observed
in some specimens of iron ore. Masses of this kind were found in
Magnesia, and from that locality we derive the name given to iron in
its polar condition. This is confirmed by the following lines by
Lucretius:--
Quod superest agere incipiam, quo fœdere fiat
Natura lapis hic ut ferrum ducere possit,
Quem magnêta vocant patrio de nomine Graii
Magnêtum, quia sit patriis in finibus ortus.
Again we find Pliny employing the term _magnetic_, to express this
singular power. It was known to the ancients that the magnetic power
of iron, and the electric property of amber, were not of the same
character, but they were both alike regarded as miraculous. The Chinese
and Arabians seem to have known Magnetism at a period long before
that at which Europeans became acquainted with either the natural
loadstone or the artificial magnet. Previously to A.D. 121, the magnet
is distinctly mentioned in a Chinese dictionary; and in A.D. 419 it
is stated in another of their books that ships were steered south by
it.[170]
The earliest popularly received account of its use in Europe is, that
Vasco de Gama employed a compass in 1427, when that really adventurous
navigator first explored the Indian seas. It is highly probable,
however, that the knowledge of its important use was derived from some
of the Oriental nations at a much earlier period.
We have some curious descriptions of the _leading stone_ or loadstone,
in the works of an Icelandic historian, who wrote in 1068. The
mariner’s compass is described in a French poem of the date of 1181;
and from Torfæus’s History of Norway, it appears to have been known to
the northern nations certainly in 1266.
We have not to deal with the history of magnetic discovery, but so
far as it tells of the strange properties which magnets are found to
possess, and the application of this knowledge to the elucidation of
effects occurring in nature.
A brown stone, in no respect presenting anything by which it shall be
distinguished from other rude stones around it, is found, upon close
examination, to possess the power of drawing light particles of iron
towards it. If this stone is placed upon a table, and iron filings
are thrown lightly around it, we discover that these filings arrange
themselves in symmetric curves, proceeding from some one point of the
mass to some other; and upon examining into this, we shall find that
the iron which has once clung to the one point will be rejected by the
other. If this stone is freely suspended, we shall learn also that
it always comes to rest in a certain position,--this position being
determined by these points, and some attractive force residing in the
earth itself. These points we call its poles; and it is now established
that this rude stone is but a small representative of our planet. Both
are magnetic: both are so in virtue of the circulation of currents
of electricity, or of lines of magnetic force, as seen in the curves
formed by the iron dust, and the north pole of the one attracts the
south pole of the other, and the contrary. By a confusion of terms we
speak of the north pole of a compass-needle, meaning that point which
is always opposite to the north pole of the earth: the truth being
that the pole of the compass-needle, which is so forcibly drawn to the
north, is a point in a contrary state, or, as we may express it, really
a south pole.
There is a power of a peculiar kind, differing from gravitation, or any
other attracting or aggregating force with which we are acquainted,
which exists permanently in the magnetic iron stones, and also in the
earth. What is this power?
Magnetism may be produced in any bar of steel, either by rubbing it
with a loadstone, or by placing it in a certain position in relation to
the magnetic currents of the earth, and, by a blow or any other means,
disturbing its molecular arrangement. This principle appears to involve
the iron as with an atmosphere, and to interpenetrate it. By one magnet
we may induce magnetism in any number of iron bars without its losing
any of its original force. As we have observed of the electrical forces
already considered, the magnet constantly presents two points in
which there is a difference manifested by the circumstance that they
are always drawn with considerable power towards the north or south
poles of the earth. That this power is of the same character as the
electricity which we have been considering, is now most satisfactorily
proved. By involving a bar of soft iron which, being without any
magnetic power, is incapable of sustaining even an ounce weight, with a
coil of copper wire, through which a galvanic current is passing, the
bar will receive, by induction from the current, an enormous accession
of power, and will, so long as the current flows around it, sustain
many hundred pounds weight, which, the moment the current is checked,
fall away from it in obedience to the law of gravity. Thus the mere
flow of this invisible agent around a mass of metal possessing no
magneto-attractive power, at once imparts this life-like influence to
it, and as long as the current is maintained, the iron is endowed with
this surprising energy.
This discovery, which we owe to the genius of Oersted, and which has,
indeed, given rise to a new science, electro-magnetism, may be regarded
as one of the most important additions made to our knowledge.
Current electricity is magnetic; iron is not necessary to the
production of magnetic phenomena, although by its presence we secure a
greater amount of power. The copper wires which complete the circuit
of a galvanic battery, will attract and hold up large quantities of
iron filings, and the wires of the electric telegraph will do the same,
while any signal is being conveyed along them. Again, all the phenomena
common to galvanic electricity can be produced by merely disturbing the
power permanently secured in the ordinary magnet. It was thought that
magnets would become weakened by this constant disturbance of their
magnetism; but, since its application to the purpose of manufacture,
and magneto-electricity has been employed in electro-plating, it has
been found that continued action for many years, during which enormous
quantities of electricity have been thus given out and employed in
producing chemical decomposition, has not, in the slightest degree,
altered their powers. Thus a small bar of metal is shown to be capable
of pouring out, for any number of years, the principle upon which the
phenomena of magnetism depend.
There are, however, differences, and striking ones, between ordinary
and magnetic electricity. In the magnet we have a power at rest, and in
the electrical machine or galvanic battery, a power in motion. Ordinary
electricity is stopped in its passage by a plate of glass, of resin,
and many other substances; but magnetism passes these with freedom, and
influences magnetic bodies placed on the other side. It would appear,
though we cannot explain how, that magnetism is due to some lateral
influence of the electric currents. A magnetic bar is placed over a
copper wire, and it hangs steadily in the direction of its length;
an electric current is passed along it, and the magnet is at once
driven to place itself across the wire. Upon this experiment, in the
main, Ampère founds his theory of terrestrial magnetism. He supposes
electrical currents to be traversing our globe from east to west, and
thus, that the needle takes its direction, not from the terrestrial
action of any fixed magnetic poles, but from the repulsion of these
currents, as is the case with the wire.
It has been found that wires, freely suspended, along which currents
were passing in opposite directions, revolve about each other, or have
an inclination to place themselves at right angles; thus exhibiting
the same phenomenon as the magnet and the conducting wire. So far the
hypothesis of Ampère leads us most satisfactorily. We see in the magnet
one form of electricity, and in the machine or battery another. But why
should not the electricity of the magnet, electricity at rest, exhibit
the same powers as this force in motion?
Oersted, whose theory led him to the discovery of the fact of the
magnetic power of an electric current, of the establishment indeed of
the new science--ELECTRO-MAGNETISM, regards the phenomena of a current
passing a wire, and its action on a needle, as evidence of two fluids,
positive and negative, traversing in opposite directions, and mutually
attracting and repelling. He conceives that they pass the wires in a
series of spirals; that in the magnet, by some peculiar property of the
iron, this conflict of the currents is reduced to an equilibrium, and
its power becomes manifested in its attractive force.[171] This does
not, however, convey a clear idea to the mind.
It is curious that iron becomes magnetic in a superior degree to any
other metal; that steel retains permanently any magnetism imparted
to it; but that soft iron rapidly loses its magnetic power. This
must be in virtue of some peculiar arrangement of the molecules, or
some unknown physical condition of the atoms of the mass, by which a
continued influence is retained by the steel, probably in a state of
constant internal circulation. It has, however, been shown that soft
iron, under certain circumstances, may be made to retain a large amount
of magnetic force.[172]
If a horse-shoe shaped bar of soft iron is rendered magnetic by the
circulation of an electric current around it, while its two ends are
united by an armature of soft iron, so that it is capable of supporting
many hundred pounds weight; and we then, by breaking the circuit, stop
the current, taking care the armature is kept in contact, the iron will
not lose its magnetic property, but will retain this power for many
years. If the connecting piece of iron, the armature, is removed, the
bar immediately loses all its magnetism, and will not support even the
armature itself. This fact appears to confirm the idea that magnetism
is due to the retention of electricity, and that steel possesses
the property of equalizing the opposing forces, or of binding this
principle to itself like an atmosphere.
The influence of heat on magnetism is so remarkable a proof of the
dependence of this power upon molecular arrangement, that it must not
escape our notice. To select but one of many experiments by Mr. Barlow,
it was found that in a bar of malleable iron, in which, when cold, the
magnetic effect was + 30° 0', all polarity ceased at a white heat, that
it was scarcely appreciable at a red heat, but that at a blood-red heat
it was equal to + 41° 0'.[173]
The more closely we examine the peculiarities of the magnetic power,
and particularly as they are presented to us in its terrestrial action,
the more surprising will its influence appear to be. We have discovered
a natural cause which certainly exercises a very remarkable power
over matter, and we have advanced so far in our investigations as to
have learnt the secret of converting one form of force into another,
or of giving to a principle, produced by one agency, a new character
under new conditions; of changing, in fact, electricity into magnetism,
and from magnetism again evolving many of the effects of electrical
currents.
If a magnetic bar is freely suspended above the earth, it takes,
in virtue of some terrestrial power, a given direction, which is
an indication of the earth’s magnetic force. Whether this is the
consequence of the currents of electricity, which Ampère supposes to
circulate around the globe, from east to west, or the result of points
of attraction in the earth itself, the phenomenon is equally wonderful.
To whatever cause we may refer the visible effects, it appears certain
that this earth is composed of particles in a magnetic state, the
character varying with physical conditions, and that terrestrial
magnetic force is the collective action of all the atoms of this
planetary mass.[174]
The remarkable connexion which has been observed between the changes
in the physical condition of the surface of the sun and terrestrial
phenomena, must not escape our notice. Sir William Herschel thought
he perceived a link connecting the dark spots on the sun’s face with
the variations of the earth’s temperature. This has not, however, been
confirmed by the observations which have been made since the time
of Herschel. The careful examinations of the solar spots which have
been made by Schwabe,[175] prove a well-defined order of progress in
them. He has discovered that they move in cycles of ten years--from
the smallest number visible in a given year, they regularly increase
for five years, when they reach their maximum; they then as regularly
decrease, and at the end of another five years they are at their
maximum number. The magnetic observations which have been carried on by
the British and other governments for some years, over every part of
the world, have elicited the fact that the order of variation in the
earth’s magnetic intensity is in cycles of ten years, and the law of
increase and decrease which is found to prevail with the solar spots
distinctly marks the variations of terrestrial magnetism. Few more
interesting facts than this are within the range of our knowledge,
proving as it does the direct dependence of terrestrial phenomena on
solar force.
The constancy with which a magnetised needle points along a certain
line which varies a little from the earth’s axial line, renders it one
of the most important instruments to the practical and the scientific
man. The wanderer of the ocean or of the desert is enabled, without
fear of error, to pursue his path, and in unknown regions to determine
the azimuth of objects. The miner or the surveyor finds in the
magnetic compass the surest guide in his labours, and the experiment is
for ever studying its indications.
“True as the needle to the pole,”
has passed into a proverb among mankind, but the searching inquiry
of modern observers has shown that the expression is correct only
with certain limitations. There are two lines on the surface of the
earth along which the needle points true north, or where the magnetic
and the geographical north correspond. These are called lines of _no
variation_, or, as they have also been designated, _agonic lines_, and
one is found in the eastern and the other in the western hemisphere.
The American line is singularly regular, passing in a south-east
direction from the latitude 60° to the west of Hudson’s Bay, across the
American lakes, till it reaches the South Atlantic ocean, and cuts the
meridian of Greenwich in about 65° south latitude. The Asiatic line
of _no variation_ is very irregular, owing, without doubt, to local
interferences; it begins below New Holland, in latitude 60° south,
it bends westward across the Indian ocean, and from Bombay has an
inflection eastward through China, and then northward across the sea
of Japan, till it reaches the latitude of 71° north, when it descends
again southward, with an immense semicircular bend, which terminates in
the White Sea.
Hansteen has thought that there are two points in each hemisphere which
may be regarded as stronger and weaker poles on opposite sides of the
poles of revolution. These are called the magnetic poles of the earth,
or by Hansteen _magnetic points of convergence_. These four points are
considered to have a regular motion round the globe, the two northern
ones from west to east, and the two southern ones from east to west. By
the assistance of recorded observations, Hansteen has calculated the
periods of these revolutions to be as follows:--
The weakest north pole in 860 years.
The strongest north pole in 1746 years.
The weakest south pole in 1304 years.
The strongest south pole in 4609 years.
There are some points of speculation on which Hansteen has ventured
which have been smiled at as fanciful; but they may rather indicate
an amount of knowledge in the Brahminical and Egyptian priesthood,
beyond what we are usually disposed to allow them, and prove that their
observations of nature had led them to an appreciation of some of the
most remarkable harmonies of this mysterious creation.
The above terms are exceedingly near 864, 1246, 1728, 4320, and those
numbers are equal to the mystic number of the Indians, Greeks, and
Egyptians, 432 multiplied by 2, 3, 4, and 10. On these the ancients
believed a certain combination of natural events to depend, and,
according to Brahminical mythology, the duration of the world is
divided into four periods, each of 432,000 years. Again, the sun’s mean
distance from the earth is 216 radii of the sun, and the moon’s mean
distance 216 radii of the moon, each the half of 432. Proceeding with
this very curious examination, Hansteen says, 60 multiplied by 432
equals 15,920, the smallest number divisible at once by all the four
periods of magnetic revolution, and hence the shortest time in which
the four poles can complete a cycle, and return to their present state,
and _which coincides exactly with the period in which the precession
of the equinoxes will amount to a complete circle_, reckoning the
precession at a degree in seventy-two years.[176]
When we consider the phenomena of terrestrial magnetism carefully, it
appears to indicate the action of a power external to the earth itself,
and, as Hansteen conceives, having its origin from the action of the
sun, heating, illuminating, and producing a magnetic tension, in the
same manner as it produces electrical excitation and actino-chemical
action.
The movements of these magnetic poles have been the subject of
extensive and most accurate observation in every quarter of the globe.
In London, during 1657-1662, there was no magnetic variation; the
agonic line passing through it. The variation steadily increased,
until, in 1815, it amounted to 24° 15' 17", since which time it has
been slowly diminishing. In addition to this great variation, we
have a regular annual change dependent on the position of the sun,
in reference to the equinoctial and solstitial points, which was
discovered by Cassini, and investigated by Arago and others. Also a
diurnal variation, which movement appears to commence early in the
morning, moving eastward until half-past seven, A.M., when it begins
to move westward until two, P.M., when it again returns to the east,
and in the course of the night reaches the point from which it started
twenty-four hours before.
We have also remarkable variations in what is termed the _dip_ of
the needle. It is well known that a piece of unmagnetized steel, if
carefully suspended by its centre, will swing in a perfectly horizontal
position, but, if we magnetize this bar, it will immediately be drawn
downwards at one end. The force of the earth’s polarity, attracting the
dissimilar pole, has caused it to _dip_.
There is, in the neighbourhood of the earth’s equator, and cutting it
at four points, an irregular curve, called the magnetic equator, or
_aclinic_ line, where the needle balances itself horizontally. As we
proceed from this line towards either pole the dip increases, until,
at the north and south poles, the needle takes a vertical position.
The _intensity_ of the earth’s magnetism is also found to vary with
the position, and to increase in a proportion which corresponds very
closely with the dip. But the _intensity_ is not a function of the
dip, and the lines of equal intensity, _isodynamic lines_, are not
parallel to those of equal dip. We have already remarked on the diurnal
variation of the declination of the needle; we know, also, that there
exists a regular monthly and daily change in the magnetic intensity.
The greatest monthly change appears when the earth is in its perihelion
and aphelion, in the months of December and June,--a maximum then
occurs; and about the time of the equinoxes a minimum is detected.[177]
The daily variation of intensity is greatest in the summer, and least
in the winter. The magnetism is generally found to be at a minimum when
the sun is near the meridian; its intensity increasing until about six
o’clock, when it again diminishes.[178]
What striking evidences all these well-ascertained facts give of the
dependence of terrestrial magnetism on solar influence! and in further
confirmation of this view, we find a very remarkable coincidence
between the lines of equal temperature--the isothermal lines, and those
of equal dip and magnetic intensity.
Sir David Brewster first pointed out that there were in the northern
hemisphere two poles of maximum cold; these poles agree with the
magnetic points of convergence; and the line of maximum heat, which
does not run parallel to the earth’s equator, is nearly coincident with
that of magnetic power. Since Seebeck has shown us that electrical
and magneto-electrical phenomena can be produced by the action of heat
upon metallic bars, we have, perhaps, approached towards some faint
appreciation of the manner in which the solar calorific radiations may,
acting on the surface of our planet, produce electrical and magnetic
effects. If we suppose that the sun produces a disturbance of the
earth’s electricity along any given line, in all directions at right
angles to that line, we shall have magnetic polarity induced.[179] That
such a disturbance is regularly produced every time the sun rises, has
been sufficiently proved by many observers.
In 1750, Wargentin noticed that a very remarkable display of _Aurora
borealis_ was the cause of a peculiar disturbance of the magnetic
needle; and Dr. Dalton[180] was the first to show that the luminous
rays of the Aurora are always parallel to the dipping-needle,
and that the Auroral arches cross the magnetic meridian at right
angles. Hansteen and Arago have attended with particular care to
these influences of the northern lights, and the results of their
observations are:--
That as the crown of the Aurora quits the usual place, the
dipping-needle moves several degrees forward:--
That the part of the sky where all the beams of the Aurora unite, is
that to which a magnetic needle directs itself, when suspended by its
centre of gravity:--
That the concentric circles, which show themselves previously to the
luminous beams, rest upon two points of the horizon equally distant
from the magnetic meridian; and that the most elevated points of each
arch are exactly in this meridian.[181]
It does not appear that every Aurora disturbs the magnetic needle; as
Captains Foster and Back both describe very splendid displays of the
phenomenon, which did not appear to produce any tremor or deviation
upon their instruments.[182]
Some sudden and violent movements have been from time to time observed
to take place in suspended magnets; and since the establishment of
magnetic observatories in almost every part of the globe, a very
remarkable coincidence in the time of these agitations has been
detected. They are frequently connected with the appearance of Aurora
borealis; but this is not constantly the case. These disturbances
have been called _magnetic storms_; and over the Asiatic and European
continent, the islands of the Atlantic and the western hemisphere, they
have been proved to be simultaneous.
From observations made at Petersburg by Kupffer, and deductions drawn
from the observations obtained by the Magnetic Association, it appears
probable that these _storms_ arise from a sudden displacement in the
magnetic lines of the earth’s surface; but the cause to which this may
be due is still to be sought for.
In the brief and hasty sketch which has been given of the phenomena
of terrestrial magnetism, enough has been stated to show the vast
importance of this very remarkable power in the great operations
of nature. We are gradually reducing the immense mass of recorded
observations, and arriving at certain laws which are found to prevail.
Still, the origin of the force, whether it is strictly electrical,
whether it is the circulation of a magnetic fluid, or whether it is
merely a peculiar excitation of some property of matter, are questions
which are open for investigation.
In the beautiful Aurora borealis, with its trembling diffusive lights,
and its many-coloured rays, we have what may be regarded as a natural
exhibition of magnetism, and we appear to have within our grasp the
explanation we desire. But we know not the secret of even these
extraordinary meteorological displays. If we pass an electric spark
from a machine through a long cylinder, exhausted of air as far as
possible, we have a mimic representation of the Northern Lights--the
same attenuation of brightness, almost dwindling into phosphorescence;
and by the slightest change of temperature we may produce that play
of colours which is sometimes so remarkably manifested in Aurora. Dr.
Dalton considered Aurora borealis _as a magnetic phenomenon, and that
its beams are governed by the earth’s magnetism_. We know that the arc
of light produced between the poles of a powerful galvanic battery is
readily deflected by a good magnet; and we have lately learned that
every vapour obeys the magnetic force.[183] It is, therefore, yet a
question for our consideration, does the earth’s magnetism produce
the peculiar phenomena of Aurora by acting upon electricity in a
state of glow? or have we evidence in this display of the circulation
of the magnetic fluid around our globe, manifesting itself by its
action on the ferruginous and other metallic matter, which Fusinieri
has proved to exist in the upper regions of our atmosphere.[184] That
magnetic radiations do exist, has been proved by Faraday, and that they
form lines of force perpendicular to the earth’s surface, has been
experimentally shown. Parallelograms of wire moved upon a central axis,
and connected with a galvanometer, give at every revolution indication
of an electric disturbance in all respects analogous to the production
of a current by moving wires in front of a steel magnet.
The alteration in the properties of heat, when it passes from the
radiant state into combination with matter, exhibits to us something
like what we may suppose occurs in the conversion of magnetism into
electricity or the contrary. We have a subtile agent, which evidently
is for ever busy in producing the necessary conditions of change in
this our earth: an element to which is due the development of many of
the most active powers of nature; performing its part by blending with
those principles which we have already examined; associating itself
with every form of matter; and giving, as we shall presently see, in
all probability, the first impulses to combination, and regulating the
forms of aggregating particles.
As electricity has the power of altering the physical conditions of
the more adherent states of matter, thus giving rise to variations
of form and modes of combination, so gross matter appears to alter
the character of this agency, and thus disposes it to the several
modifications under which we have already detected its presence.
We have mechanical electricity and chemical electricity, each
performing its great work in nature; yet both manifesting conditions
so dissimilar, that tedious research was necessary before they could
be declared identical. Magnetic electricity is a third form; all its
characteristics are unlike the others, and the office it appears to
perform in the laboratory of creation is of a different order from
that of the other states of electrical force. In the first two we have
decomposing and recombining powers constantly manifested--in fact,
their influences are always of a chemical character; but in the last it
appears we have only a directive power. It was thought that evidence
had been detected of a chemical influence in magnetism; it did appear
that sometimes a retarding force was exerted, and often an accelerating
one. This has been again denied, and we have arrayed in opposition to
each other some of the first names among European experimentalists.
The question is not yet to be regarded as settled; but, from long and
tedious investigation, during which every old experiment has been
repeated, and numerous new ones tried, we incline to the conclusion
that chemical action is not directly affected by magnetic power. It
is highly probable that magnetism may, by altering the structural
arrangement of the surface, vary the rate of chemical action; but this
requires confirmation.[185]
There is no substance to be found in nature existing independently of
magnetic power. But it influences bodies in different ways: one set
acting with relation to magnetism, like iron, and arranging themselves
along the line of magnetic force,--these are called magnetic bodies;
another set, of which bismuth may be taken as the representative,
always placing themselves at right angles to this line,--these are
called _diamagnetic bodies_.[186] This is strikingly shown by means of
powerful electro-magnets; but the magnetism of the earth is sufficient,
under proper care, to exhibit the phenomena.
Every substance in nature is in one or other of these conditions. The
rocks, forming the crust of the earth, and the minerals which are
discovered in them; the surface soil, which is by nature prepared as
the fitting habitation of the vegetable world, and every tree, shrub,
and herb which finds root therein, with their carbonaceous matter, in
all its states of wood, leaf, flower, and fruit; the animal kingdom,
from the lowest monad through the entire series up to man,--have, all
of them, distinct magnetic or diamagnetic relations.
“It is a curious sight,” says Dr. Faraday, “to see a piece of wood or
of beef, or an apple, or a bottle of water repelled by a magnet, or,
taking the leaf of a tree, and hanging it up between the poles, to
observe it take an equatorial position. Whether any similar effects
occur in nature among the myriads of forms which, upon all parts of its
surface, are surrounded by air, and are subject to the action of lines
of magnetic force, is a question which can only be answered by future
observation.”[187]
At present, the bodies which are known to exhibit decided
ferro-magnetic properties are the following, which stand arranged in
the order of their intensity:--
Iron, Nickel, Cobalt, Manganese,
Chromium, Cerium, Titanium,
Palladium, Platinum, Osmium.
It is interesting to know that there are evidences that two bodies
which, when separate, are not magnetic, as iron is, become so when
combined. Copper and zinc are both of the diamagnetic class, but many
kinds of brass are discovered to be magnetic.
The salts of the above metals are, to a greater or less extent,
ferro-magnetic, but they may be rendered neutral by water, which is a
diamagnetic body, being repelled by the magnet. It will be unnecessary,
here, to enumerate the class of bodies which are diamagnetic; indeed,
all not included in the preceding list may be considered as belonging
to that class, with the exception of gases and vapours, which appear
to exist, relatively to each other, sometimes in the one, and sometimes
in the other condition.[188]
To endeavour to reduce our knowledge of these facts to some practical
explanation, we must bear in mind that particular spaces around the
north and south geographical poles of the earth, are regarded as
circles to which all the magnetic lines of force converge. Under
circumstances which should prevent any interference with what is called
ferro-magnetic action, all bodies coming under that class would arrange
themselves according to the laws which would regulate the disposition
of an infinite number of magnets, free to move within the sphere of
each other’s influence. The north and south pole of one magnetic body
would attach itself to the south and north pole of another, until we
had a line of magnets of any extent; the two ends being in opposite
states, like the magnetic points of convergence of the earth.
Every body, not ferro-magnetic, places itself across such a line of
magnetic force as we have conceived; and if the earth were made up of
separate layers of ferro-magnetic and diamagnetic bodies, the result
would be the formation of bands at right angles to each other. This
is not the case, by reason of the intermingling of the two classes
of substances. Out of the known chemical elements we find only about
ten which are actively ferro-magnetic; the others combining with
these give rise to either a weaker state, a neutral condition, or
the balance of action is turned to the diamagnetic side. Sulphate of
iron, for instance, is a magnetic salt; but in solution, water being
diamagnetic, it loses its property. The yellow prussiate of potash
dissolved in water is a diamagnetic body; but the red prussiate, which
contains an atom less of potassium, is magnetic: but in the solid state
they are both diamagnetic.[189]
From this it would appear that the chemical composition of a body
regulated its relation to magnetism. The following facts will show,
however, that the molecular structure is more particularly concerned in
determining the molecular condition of substances.
M. Plücker, being desirous of finding the extent to which the
_direction of the fibres_ in organic bodies might influence their
magnetic or diamagnetic properties, was led to inquire whether in
crystals the direction of the optic axes, which itself depends upon the
arrangement of the particles, might not also exercise some influence.
The first submitted to the action of the electro-magnet a thin plate
of tourmaline, such as is employed in experiments upon polarization,
having its optic axis parallel to its longest length. It was very
quickly perceived that the plate was magnetic, by the effect of the
iron that it contains; but it was suspended successively in three
ways,--first, so that its longest side was vertical, then as that the
shortest side was vertical, and finally so that the plate itself was
horizontal. In the first case it is directed between the two points
of the conical curvatures of the poles like a magnetic body; but, in
the other two cases, on the contrary, it took the direction assumed by
diamagnetic bodies--that is to say, a direction such that its longest
length was perpendicular to the line joining the poles. This direction
indicated that the optical axis was repelled by the two poles, and that
this repulsion outweighed the magnetic properties of the crystal.[190]
The relation of structure to physical phenomena of essentially
different characters is remarkable. Savart, when making crystalline
plates of quartz and carbonate of lime vibrate, succeeded in
determining a relation between the acoustic figures that are
produced in them, and the particular mode of the crystallization of
the substance. He found that the direction of the optical axis is
constantly connected with that of the principal forms of the acoustic
figures.
Mitscherlich has remarked that crystals do not expand uniformly by
heat, but that this dilatation is greater in one direction than in
another; and that this difference is connected with their crystalline
form. M. de Sénarmont has shown that conductibility for heat,
which is equal in all directions for the crystals of the regular
system, acquires in others a maximum or a minimum value, according
to directions parallel to the crystallographic axes; so that the
isothermic surfaces, which are spheres in the former case, are, in the
other, ellipsoids elongated or flattened in the same direction. The
optical axes do not altogether coincide with the principal axes of
conductibility for heat; but this appears to be due merely to slight
differences in the rate of progression, or the refrangibility of the
luminous and calorific rays.
Wiedemann, by employing a fine point through which he made electricity
arrive upon a surface that he had powdered with licopodium or red lead,
succeeded in determining, by means of the form assumed by this light
powder, the conductibility of crystals in different directions.
On a surface of glass, the powder which disperses itself around the
points, in consequence of electric repulsion, forms a circular
figure traversed by radii. When a plate of gypsum is used instead of
glass the figure is found to be elliptical, and the great axis of
the ellipse forms a right angle with the principal crystallographic
axis, which proves that the electricity distributes itself more
easily in a direction perpendicular to the axis than in any other.
M. Wiedemann comes to the conclusion that crystals which possess a
better conductibility in the direction of the principal axis, all
belong to the class of negative crystals: while those which have a
better conductibility in the direction perpendicular to the axis are
positive, which indicates that the direction of best conductibility
for electricity is also that according to which light is propagated
relatively with greater velocity.
Tyndale has shown, that if gutta percha which has been rendered fibrous
in manufacture is cut so that the fibres are in the direction of this
greatest length, or in a direction perpendicular to this greatest
length, and placed under the influence of a magnet, they direct
themselves equatorially. Ivory cut in the same direction manifests the
same conditions, though both these substances are diamagnetic.
The fibrous structure, and the planes of cleavage, thus determine the
magnetic condition of a substance. The special properties presented by
crystals, in regard to the action exercised upon them by magnets, is
due to a particular mode of grouping their particles. This is also the
cause of unequal dilatability, and of unequal conductibility for heat
and for electricity.
How curiously, therefore, does molecular structure determine the
relation of a body to any of the forms of physical force!
We still search in the dark, and see but dimly the evidences; yet it
becomes almost a certainty to us, that this stone of granite, with its
curious arrangement of felspar, mica, and quartz, presents its peculiar
condition in virtue of some law of magnetic force. The crystal, too,
of quartz, which we break out of the mass, and which presents to us a
beautifully regular figure, is, beyond a doubt, so formed, because the
atoms of silica are each one impelled in obedience to one of these two
conditions of magnetism to set themselves in a certain order to each
other, which cannot be altered by human force without destruction.
All the laws which regulate the forms of crystals and amorphous bodies
are, to the greatest degree, simple. In nature the end is ever attained
by the easiest means; and the complexity of operation, which appears
sometimes to the observer, is only so because he cannot see the spring
by which the machine is moved.
The gaseous envelope, our atmosphere, is in a neutral state. Oxygen is
strikingly magnetic in relation to hydrogen gas, whilst nitrogen is as
singularly the contrary; and the same contrasts present themselves when
these gases are examined in their relation to common air. Thus, oxygen
being magnetic, and nitrogen the contrary, we have an equilibrium
established, and the result is a compound neutral in its relations to
all matter. All gases and vapours are found to be diamagnetic, but in
different degrees.[191] This is shown by passing a stream of the gas,
rendered visible by a little smoke, within the influence of a powerful
magnet.
These bodies are, however, found relatively to each other,--or even
to themselves, under different thermic conditions,--to change their
states, and pass from the magnetic to the diamagnetic class. Heat has a
very remarkable influence in altering these relations; and atmospheric
air at one temperature is magnetic to the same fluid at another: thus,
by thermic variations, attraction or repulsion may be alternately
maintained. By this it must be understood that a stream of air, at a
temperature elevated but a few degrees above that of an atmosphere of
the same kind into which it is passing, is deflected in one way by a
magnet; whereas, if the stream is colder than the bulk through which
it flows, it is bent in another way by the same force. In this respect
magnetism and diamagnetism show equally the influence of another
physical force, heat; and we may safely refer many meteorological
phenomena to similar alterations of condition in the atmosphere,
relative to the magnetic relations of the aërial currents.
That magnetism has a directive power is satisfactorily shown by
the formation of crystals in the neighbourhood of the poles of
powerful magnets. The common iron salt, the protosulphate, ordinarily
crystallizes so that the crystals unite by their faces; but when
crystallizing under magnetic influence, they have a tendency to arrange
themselves with regard to each other so that the acute angle of one
crystal unites with one of the faces of another crystal, near to, but
never actually at, its obtuse angle. In addition to this, if a magnet
of sufficient power is employed, the crystals arrange themselves in
magnetic curves from one pole to the other, a larger crop of crystals
being always formed at the north than at the south pole. Here we have
evidence of an actual turning round of the crystal, in obedience to the
directive force of the magnet; and we have the curious circumstance of
a difference in some way, which is not clearly explained, between the
two opposite poles. If, instead of an iron or a ferro-magnetic salt,
we employ one which belongs to the other, or diamagnetic, class, we
have a curious difference in the result. If into a glass dish, fixed
on the poles of a strong electro-magnet, we pour a quantity of a
solution of nitrate of silver, and place in the fluid, over the poles
of the magnet, two globules of mercury (an arrangement by which that
arborescent crystallization, called the _Arbor Dianæ_, is produced,) we
have the long needle-shaped crystals of silver, arranging themselves in
curves which would cut the ordinary magnetic lines at right angles.[192]
In the first example given we have an exhibition of magnetic force,
while in the last we have a striking display of the diamagnetic power.
The large majority of natural formations appear to group themselves
under the class of diamagnetics. These bodies are thought to possess
poles of mutual repulsion among themselves, and which are equally
repelled by the magnetic points of convergence. Confining our ideas to
single particles in one condition or the other, we shall, to a certain
extent, comprehend the manifold results which must arise from the
exercise of these two modes of force. At present, our knowledge of the
laws of magnetism is too limited to allow of our making any general
deductions relative to the disposition of the molecules of matter; and
the amount of observation which has been given to the great natural
arrangements, is too confined to enable us to infer more than that it
is probable many of the structural conditions of our planet are due to
polarity.
Mountain ranges observe a singular uniformity of direction, and
the cleavage planes of rock are evidently determined by some
all-pervading power. Mineral bodies are not distributed in all
rocks indiscriminately. The primary formations hold one class of
metalliferous ores, and the more recent ones another. This is not
to be regarded as in any way connected with their respective ages,
but with some peculiar condition of the stone itself. The granite
and slate rocks, at their junctions, present the required conditions
for the deposit of copper ore, while we find the limestones have the
characteristic physical state for accumulating lead ore. Again, on
examining any mineral vein, it will be at once apparent that every
particle of ore, and every crystal of quartz or limestone, is disposed
in a direction which indicates the exercise of some powerful directive
agency.[193]
It appears, from all the results hitherto obtained, that the magnetic
and diamagnetic condition of bodies is equally due to some peculiar
property of matter in relation to the other forms of electricity. We
have not yet arrived at the connecting link, but it does not appear to
be far distant.
We have already referred to the statement made by talented
experimentalists, that magnetism has a powerful influence in either
retarding or accelerating chemical combination. Beyond a doubt chemical
action weakens the power of a magnet; but the disturbance which it
occasions in soft iron, on the contrary, appears to tend to its
receiving magnetism more readily, and retaining it more permanently.
Further investigations are, however, required, before we can decide
satisfactorily either of these problems, both of which bear very
strongly upon the subject we have just been considering.
We have seen that heat and electricity act strangely on magnetic force,
and that this statical power reacts upon them: and thus the question
naturally arises, Do light and magnetism in any way act upon each other?
Morichini and Carpi on the continent, and Mrs. Somerville in England,
have stated that small bars of steel can be rendered magnetic by
exposing them to the influence of the violet rays of light. These
results have been denied by others, but again repeated and apparently
confirmed. In all probability, the rays to which the needles were
exposed, being those in which the maximum actinic power is found,
produced an actual chemical change; and then, if the position were
favourable, it is quite evident that magnetism would be imparted.
Indeed we have found this to be the case when the needles, exposed to
solar radiations, were placed in the direction of the dip. The supposed
magnetization of light by Faraday has already been mentioned. If the
influence in one case is determined, it will render the other more
probable.[194]
“In seeking for a cause,” writes Sir David Brewster, “which is capable
of inducing magnetism on the ferruginous matter of our globe, whether
we place it within the earth, or in its atmosphere, we are limited to
the SUN, to which all the magnetic phenomena have a distinct reference;
but, whether it acts by its heat, or by its light, or by specific
rays, or influences of a magnetic nature, must be left to future
inquiry.”[195]
We have learnt that magnetism is not limited to ferruginous matter; we
know that the ancient doctrine of the universality of the property is
true. Kircher, in his strange work on Magnetism, published in the early
part of the seventeenth century[196]--a curious exemplification of the
most unwearying industry and careful experiment, combined with the
influences of the credulity and superstitions of his age--attributes to
this power nearly all the cosmical phenomena with which, in his time,
men were acquainted. He curiously anticipates the use of the supposed
virtue of magnetic traction in the curative art; and as the titles of
his concluding chapters sufficiently show, he was a firm believer in
animal magnetism.[197] But it is not with any reference to these that
we refer to the work of _Athanasii Kircheri, Societatis Jesu, Magnes,
sive de Magnetivâ Arte_, but to show that two hundred years since,
man was near a great truth; but the time of its development being not
yet come, it was allowed to sleep for more than two centuries, and
the shadow of night had covered it. In speaking of the vegetable
world, and the remarkable processes by which the leaf, the flower,
and the fruit are produced, this sage brings forward the fact of the
diamagnetic character of the plant, which has been, within the last two
years, re-discovered; and he refers the motions of the Sun-flower, the
closing of the Convolvulus, and the directions of the spiral, formed by
twining plants, to this particular influence.
This does not appear as a mere speculation, a random guess, but is
the result of deductions from experiment and observation. Kircher
doubtless leaped over a wide space to come to his conclusion; but the
result is valuable in a twofold sense. In the first it shows us that,
by neglecting a fact which is suggestive, we probably lose a truth
of great general application; and secondly, it proves to us, that by
stepping beyond the point to which inductive logic leads, and venturing
on the wide sea of hypothesis, we are liable to sacrifice the true to
the false, and thus to hinder the progress of human knowledge.
Magnetism, in one or other of its forms, is now proved to be universal,
and to its power we are disposed to refer the structural conditions
of all material bodies, both organic and inorganic. This view has
scarcely yet been recognised by philosophers; but as we find a certain
law of polarity prevailing through every atom of created matter, in
whatever state it may be presented to our senses, it is evident that
every particle must have a polar and directing influence upon the mass,
and every coherent mass becomes thus only a larger and more powerful
representative of the magnetic unit. Thus we see the speculation of
Hansteen, that the sun is, to us, a magnetic centre, and that it
is equally influenced by the remoter suns of the universe,[198] is
supported by legitimate deductions from experiment.
The great difficulty is not, however, got rid of by this speculation;
the cause by which the earth’s magnetism is induced is only removed
further off.
The idea of a magnetic fluid is scarcely tenable; and the ferruginous
nature of the Aurora borealis receives no proof from any investigation;
indeed, we have procured evidence to show that iron is not at all
necessary for the production of magnetic phenomena. The leaf of a
tree, a flower, fruit, a piece of animal muscle, glass, paper, and a
variety of similar substances, have the power of repelling the bar of
iron which we call a magnet, and of placing it at right angles to the
direction of the force exerted by them. This is a point which must be
constantly borne in mind when we now consider the mysteries of magnetic
phenomena.
Any two masses of matter act upon each other according to this law,
and although by the power of cohesion the force may be brought to an
equilibrium, or to its zero point, it is never lost, and may be readily
and rapidly manifested by any of the means employed for electrical
excitation.
Reasoning by analogy, the question fairly suggests itself: If two
systems of inorganic atomic constitution are thus invested with a
power of influencing each other through a distance, why may not
two more highly developed organic systems equally, or to a greater
extent, produce an influence in like manner? Upon such reasoning as
this is founded the phenomenon known as Animal Magnetism. There is no
denying the fact that one mass of blood, muscle, nerves, and bone,
must, magnetically, influence another similar mass. This is, however,
something totally different from that abnormal condition which is
produced through some peculiar and, as yet, unexplained physiological
influences.
With the mysterious operations of vital action, the forces which we
have been considering have nothing whatever in common. The powers
which are employed in the arrangements of matter are, notwithstanding
their subtile character, of far too gross a nature to influence the
psychological mysteries which present themselves to the observant
mind. It cannot be denied that, by placing a person of even moderate
nervous sensibility in a constrained position, and under an unnatural
influence of the mind, as acquired by the disciples of Mesmer, a torpor
affecting only certain senses is produced. The recognised and undoubted
phenomena are in the highest degree curious--but in these the marvels
of charlatanry and ignorance are not included;--and the explanation
must be sought for by the physiologist among those hidden principles
upon which depends all human sensation.[199]
Man, like a magician, stands upon a promontory, and surveying the great
ocean of the physical forces which involve the material creation,
and produce that infinite variety of phenomena which is unceasingly
exhibited around him, he extends the wand of intelligence, and bids the
“spirits of the vasty deep” obey his evocation.
The phenomena recur--the great processes of creation go on--the
external manifestations of omnipotent power proceed--effects are
again and again produced; but the current of force passes undulating
onwards;--and to the proud bidding of the evocator there is no reply
but the echo of his own vain voice, which is lost at last in the vast
immensity of the unknown which lies beyond him.
We see how powerfully the physical forces, in their various modes of
action, stir and animate this planetary mass; and amongst these the
influence of magnetism appears as a great directing agent, though its
origin is unknown to us.
That power which, like a potent spirit, guides
The sea-wide wanderers over distant tides,
Inspiring confidence where’er they roam,
By indicating still the pathway home;--
Through nature, quicken’d by the solar beam,
Invests each atom with a force supreme,
Directs the cavern’d crystal in its birth,
And frames the mightiest mountains of the earth;
Each leaf and flower by its strong law restrains,
And binds the monarch Man within its mystic chains.
FOOTNOTES:
[170] _Treatise on Magnetism_, by Sir David Brewster. _Cosmos: a
Sketch of a Physical description of the Universe_; by Alexander Von
Humboldt.--Otté’s Translation.
[171] _Expérience Electro-Magnétique._ par M. Œrsted.--Annales de
Chimie, vol. xxii. p. 201. De la Rive, _Recherches sur la Distribution
de l’Electricité dyn. dans les Corps_.--Genève, 1825.
[172] _On the Magnetic power of Soft Iron_: by Mr.
Watkins.--Philosophical Transactions, 1833.
[173] Cavallo, _On Magnetism_.--Cavallo was the first who noticed the
influence of heat on Magnetism. Consult _On the anomalous Magnetic
Action of Hot Iron between the white and blood-red heat_: by Peter
Barlow, Esq.--Philosophical Transactions, 1822, p. 124. _Treatise on
Magnetism_: by Barlow.--Encyclopædia Metropolitana.
[174] “The foundation of our researches is the assumption that the
terrestrial magnetic force is the collective action of all the
magnetised particles of the earth’s mass. We represent to ourselves
magnetisation as the separation of the magnetic fluids. Admitting the
representation, the mode of action of the fluids (repulsion of similar,
and attraction of dissimilar, particles inversely as the square of the
distance) belongs to the number of established truths. No alteration
in the results would be caused by changing this mode of representation
for that of Ampère, whereby, instead of magnetic fluids, magnetism is
held to consist in constant galvanic currents in the minutest particles
of bodies. Nor would it occasion a difference if the terrestrial
magnetism were ascribed to a mixed origin, as proceeding partly from
the separation of the magnetic fluids in the earth, and partly from
galvanic currents, in the same; inasmuch as it is known that for each
galvanic current may be substituted such a given distribution of the
magnetic fluids in a surface bounded by the current, as would exercise
in each point of external space precisely the same magnetic action as
would be produced by the galvanic current itself.”--_General Theory
of Terrestrial Magnetism_, by Professor Carl Friedrich Gauss, of the
University of Göttingen.--Scientific Memoirs, vol. ii. p. 188.
[175] Humboldt’s _Cosmos_.--Otté’s translation.
[176] Hansteen: _Untersuchungen über den Magnetismus der
Erde_, Christïana, 1819. Humboldt: _Exposé des Variations
Magnétiques_.--Gilbert’s Annales. Brewster’s Magnetism: Encyclopædia
Metropolitana.
[177] Hansteen; as above.
[178] _On the effects of temperature on the intensity of magnetic
forces, and on the diurnal variations of the terrestrial magnetic
intensity_; by Samuel Hunter Christie, Esq.--Philosophical
Transactions, vol. cxv. 1825.
[179] It has been observed by Mr. Barlow, in England, and some eminent
observers in Austria, that an electric current constantly traverses
the wires of the electric telegraph wherever there are two earth
connections.
[180] _Meteorological Observations and Essays_: by Dr. Dalton. _On the
Height of the Aurora Borealis above the surface of the Earth_: by John
Dalton, F.R.S.--Philosophical Transactions, vol. cxiv. p. 291.
[181] Arago: Annales de Chimie, vol. xxxix. p. 369. _On the variable
Intensity of Terrestrial Magnetism and the Influence of the Aurora
Borealis upon it_; by Robert Were Fox.--Philosophical Transactions,
1831, p. 199.
[182] “Brilliant and active coruscations of the Aurora Borealis,” says
Captain Back, “when seen through a hazy atmosphere, and exhibiting
the prismatic colours, almost invariably affected the needle. On the
contrary, a very bright Aurora, though attended by motion, and even
tinged with a dullish red and a yellow in a clear blue sky, seldom
produced any sensible change, beyond, at the most, a tremulous motion.
A dense haze or fog, in conjunction with an active Aurora, seemed
uniformly favourable to the disturbance of the needle, and a low
temperature was favourable to brilliant and active coruscations. On
no occasion during two winters was any sound heard to accompany the
motions. The Aurora was frequently seen at twilight, and as often to
the eastward as to the westward; clouds, also, were often perceived
in the day-time, in form and disposition very much resembling the
Aurora.”--_Narrative of the Arctic Land Expedition._
[183] Faraday: _On the Diamagnetic character of Flame and Gases_.
[184] “The Aurora Borealis is certainly in some measure a magnetical
phenomenon; and if iron were the only substance capable of exhibiting
magnetic effects, it would follow that some ferruginous particles
must exist in the upper regions of the atmosphere. The light usually
attending this magnetical meteor may possibly be derived from
electricity, which may be the immediate cause of a change in the
distribution of the magnetic fluid, contained in the ferruginous
vapours which are imagined to float in the air.”--Lecture on Magnetism:
Young’s _Lectures on Natural Philosophy_, p. 533.
[185] _On the supposed influence of Magnetism and Chemical Action_; by
Robert Hunt.--Philosophical Magazine, vol. xxxii. No. 215, 1849.
[186] Those bodies which are attracted by a magnet, as iron is, are
called _magnetic bodies_. Those which are, on the contrary, repelled by
the same power, are termed _diamagnetic bodies_. On these Dr. Faraday
remarks:--“Of the substances which compose the crust of the earth, by
far the greater portion belong to the diamagnetic class; and though
ferruginous and other magnetic matters, being more energetic in their
action, are more striking in their phenomena, we should be hasty in
assuming that, therefore, they over rule entirely the effect of the
former bodies. As regards the ocean, lakes, rivers, and the atmosphere,
they will exert their peculiar effect almost uninfluenced by any
magnetic matter in them, and as respects the rocks and mountains, their
diamagnetic influence is perhaps greater than might be anticipated.
I mentioned that by adjusting water and a salt of iron together, I
obtained a solution inactive in air; that is, by a due association
of the forces of a body, from each class, water and a salt of iron,
the magnetic force of the latter was entirely counteracted by the
diamagnetic force of the former, and the mixture was neither attracted
nor repelled: To produce this effect, it required that more than 48·6
grains of crystallised protosulphate of iron should be added to ten
cubic inches of water (for these proportions gave a solution which
would set equatorially), a quantity so large, that I was greatly
astonished on observing the power of the water to overcome it. It
is not, therefore, at all unlikely that many of the masses which
form the crust of this our globe, may have an excess of diamagnetic
power, and act accordingly.”--_On new magnetic actions, and on the
magnetic condition of all matter_; by Michael Faraday, D.C.L., F.R.S.,
&c.--Philosophical Transactions, Jan. 1846, vol. cxxxvii. p. 41.
[187] Ibid.
[188] _On the Diamagnetic conditions of Flame and Gases_, by Michael
Faraday. F.R.S.; and _On the motions presented by Flame when under
Electro-Magnetic Influence_, by Professor Zantedeschi.--Philosophical
Magazine, 1847, pp. 401-421.
[189] _On Diamagnetism_; by Professor Plücker, of Bonn.--Philosophical
Magazine, July, 1848.
[190] For a detailed account of the experiments of Faraday, Plücker,
Becquerel, Tyndale, and Knoblauch, see De La Rive’s _Treatise on
Electricity in Theory and Practice_.
[191] A few examples taken from Dr. Faraday’s paper will show this:--
Nitrogen being acted on was manifestly diamagnetic in relation to
common air when both were of the same temperature. Oxygen appears to
be magnetic in common air. Hydrogen proved to be clearly and even
strongly diamagnetic. Its diamagnetic state shows, in a striking
point of view, that gases, like solids, have peculiar and distinctive
degrees of diamagnetic force. Carbonic acid gas is diamagnetic in air.
Carbonic oxide was carefully freed from carbonic acid before it was
used, and it appears to be more diamagnetic than carbonic acid. Nitrous
oxide was moderately, but clearly, diamagnetic in air. Olefiant gas
was diamagnetic. The coal gas of London is very well diamagnetic, and
gives exceedingly good and distinct results. Sulphurous acid gas is
diamagnetic in air. Muriatic acid gas was decidedly diamagnetic in
air.--_On the Diamagnetic Conditions of Flame and Gases_: Philosophical
Magazine, 1847, p. 409.
[192] For illustration of this I must refer to my own Memoir,
_Researches on the Influence of Magnetism and Voltaic Electricity on
Crystallization, and other conditions of matter_, in the Memoirs of the
Geological Survey of Great Britain, &c., vol. i.
[193] In a work published by Mr. Evan Hopkins, entitled _On the
Connexion of Geology with Terrestrial Magnetism_, will be found many
valuable practical observations made in this country and the gold and
silver districts of America; but the views taken by the author are open
to many objections.
[194] See a notice by Faraday of Morichini’s Experiments in _Relations
of Light to Magnetic Force_--Philosophical Transactions, vol. cxxxvii.
p. 15. See also Mr. Christie _On Magnetic Influence in the Solar
Rays_--Philosophical Transactions, vol. cvii. p. 219; vol. cxix. p. 379.
[195] Sir David Brewster _On Magnetism_; republished from the
Encyclopædia Britannica.
[196] The whole of the title of Kircher’s book will convey some idea
of the subjects embraced:--Athanasii Kircheri Societatis Jesu Magnes,
sive de Arte Magneticâ; opus tripartitum, quo Universa Magnetis Natura
ejusque in omnibus Scientiis et Artibus usus novâ methodo explicatur:
ac præterea e viribus et prodigiosis effectibus Magneticarum aliarumque
abditarum Naturæ Motionum in Elementis, Lapidibus, Plantis, Animalibus
elucescentium: multa hucusque incognita Naturæ Arcana, per Physica,
Medica, Chymica, et Mathematica omnis generis Experimenta recluduntur
Editio Tertia: ab ipso Authore recognita emendataque, ac multis novorum
Experimentorum Problematibus aucta. Romæ, 1654.
[197] The following are the titles of the concluding chapters of
Kircher’s book:--_De magnetismo solis et lunæ in maria._ _De magneticâ
vi plantarum._ _De insitionis magneticis miraculis._ _De magnetismo
virgulæ auriferæ seu divinatoriæ._ _De plantis heliotropiis eorumque
magnetismo._ _De magnetismo rerum medicinalium._ _De vi attractivâ
potentiæ imaginativæ._ _De magnetismo musicæ._ _De magnetismo amoris._
[198] “For these reasons it appears most natural to seek their origin
in the sun, the source of all living activity, and our conjecture gains
probability from the preceding remarks on the daily oscillations of
the needle. Upon this principle the sun may be conceived as possessing
one or more magnetic axes, which, by distributing the force, occasion
a magnetic difference in the earth, in the moon, and all those planets
whose internal structure admits of such a difference. Yet, allowing
all this, the main difficulty seems not to be overcome, but merely
removed from the eyes to a greater distance; for the question may still
be asked, with equal justice, whence did the sun acquire its magnetic
force? And if from the sun we have recourse to a central sun, and from
that again to a general magnetic direction throughout the universe,
having the Milky Way for its equator, we but lengthen an unrestricted
chain, every link of which hangs on the preceding link, no one of them
on a point of support. All things considered, the following mode of
representing the subject appears to me most plausible. If a single
globe were left to move alone freely in the immensity of space, the
opposite forces existing in its material structure would soon arrive
at an equilibrium conformable to their nature, if they were not so at
first, and all activity would soon come to an end. But if we imagine
another globe to be introduced, a mutual relation will arise between
the two; and one of its results will be a reciprocal tendency to
unite, which is designated and sometimes thought to be explained by
the merely descriptive word Attraction. Now would this tendency be
the only consequence of this relation? Is it not more likely that the
fundamental forces, being drawn from their state of indifference or
rest, would exhibit their energy in all possible directions, giving
rise to all kinds of contrary action? The electric force is excited,
not by friction alone, but also by contact, and probably also, though
in smaller degrees, by the mutual action of two bodies at a distance;
for contact is nothing but the smallest possible distance, and that,
moreover, only for a few small particles. Is it not conceivable that
magnetic force may likewise originate in a similar manner? When the
natural philosopher and the mathematician pay regard to no other effect
of the reciprocal relation between two bodies at a distance, except
the tendency to unite, they proceed logically, if their investigations
require nothing more than a moving power; but should it be maintained
that no other energy can be developed between two such bodies, the
assertion will need proof and the proof will be hard to find.”--The
above is a translation from Hansteen’s work _On Magnetism_.
[199] See article _Animal Magnetism_, Encyclopædia Britannica, and Mr.
Braid’s papers _On Hypnotism_, published in the “Medical Times.”