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.”

CHAPTER XI.

CHEMICAL FORCES.

  Nature’s Chemistry--Changes produced by Chemical Combination--Atomic
    Constitution of Bodies--Laws of Combination--Combining
    Equivalents--Elective Affinity--Chemical Decomposition--Compound
    Character of Chemical Phenomena--Catalysis or action
    of Presence--Transformation of Organic Bodies--Organic
    Chemistry--Constancy of Combining Proportions--The Law of Volumes,
    the Law of Substitutions, Isomeric States, &c.

All things on the earth are the result of chemical combination. The
operations by which the commingling of molecules and the interchange
of atoms take place, we can imitate in our laboratories; but in nature
they proceed by slow degrees, and, in general, in our hands they are
distinguished by suddenness of action. In nature chemical power is
distributed over a long period of time, and the process of change is
scarcely to be observed. By art we concentrate chemical force, and
expend it in producing a change which occupies but a few hours at most.
Many of the more striking phenomena of nature are still mysterious to
us, and principally because we do not, or cannot, take the element time
into calculation. The geologist is compelled to do this to explain the
progress of the formation of the crust of the earth, but the chemist
rarely regards the effects of time in any of his operations. The
chemical change which within the fissure of the rock is slowly and
silently at work, displacing one element or molecule, and replacing it
by another, is in all probability the operation of a truly geological
period. Many, however, of the changes which are constantly going on
around us, are of a much more rapid character, and in these nature is
no slower in manipulating than the chemist.

Had it been that the elements which are now found in combination
could exist in a free state, the most disastrous consequences would
necessarily ensue. There must have been a period when many of the
combinations known to us were not yet created. Their elements either
existed in other forms, or were uncombined. Our rocks are compounds of
oxygen with certain peculiar metals which unite with oxygen so rapidly
that incandescence is produced by their combination. Let us suppose
that any of these metals existed in purity, and that they were suddenly
brought into contact with water, the atmospheric air, or any body
containing oxygen, the result would be a convulsion of the most fearful
kind; the entire mass of metal would glow with intensity of heat, and
the impetuosity of the action would only be subdued when the whole
of the metal had become oxidized. Volcanic action has been referred
to some such cause as this, but there is not sufficient evidence to
support the hypothesis; indeed, it is contrary to the opinion of most
philosophers.[200] Such a condition may possibly have existed at one
time, during that period when darkness was upon the face of the deep,
when the earth was a chaos; but it is only adduced here as an example
of the violent nature of some chemical changes. Potassium thrown on
water bursts into flame, and sodium does so under certain conditions.
If these, or the metals proper in a state of fine division, are brought
into an atmosphere of chlorine, the intensity of chemical action is so
great that they become incandescent, many of them glowing with extreme
brilliancy. If hydrogen gas is mixed with this element (chlorine)
they unite, under the influence of light, with explosive violence,
giving rise to a compound, muriatic acid, which combines with water
in an almost equally energetic manner. Nitrogen, as it exists in the
atmosphere, mixed with oxygen, appears nearly inert; with hydrogen it
forms the pungent compound, ammonia; with carbon, the poisonous one,
cyanogen, the base of prussic acid; with chlorine it gives rise to a
fluid, oily in its appearance, but which, when merely touched by an
unctuous body, explodes more violently than any other known compound,
shivering whatever vessel it may be contained in, to atoms; with iodine
it is only slightly less violent; and in certain combinations with
silver, mercury, gold, or platinum, it produces fulminating compounds
of the most dangerous character.[201] Here we have elements harmless
when uncombined, exhibiting the most destructive effects if their
combinations are at all disturbed; and in the other case we have inert
masses produced from active and injurious agents.

We regard a certain number of substances as _elementary_; that is to
say, not being able, in the present state of our knowledge, to reduce
them to any more simple condition, they are considered as the elements
which by combination produce the variety of substances found in the
three kingdoms of nature.

We have already spoken of the atomic constitution of bodies. It remains
now to explain the simplicity and beauty which mark every variety of
combination under chemical force. As a prominent and striking example,
water is a compound of two gaseous bodies, oxygen and hydrogen:--

If we decompose water by means of galvanic electricity, or determine
its composition by direct chemical analysis, we shall find it consists
of two volumes of hydrogen gas, united to one volume of oxygen, or, by
weight, of one part of hydrogen combined with eight of oxygen. In 100
parts, therefore, we should find--

    Oxygen        88·9
    Hydrogen      11·0

It is found in the same way that the theoretical weight of the atom
of carbon is 6, and that of nitrogen 14; whilst the atom of iron is
28, that of silver 108, of gold 199, and that of platinum and iridium
each 98.[202] Now, as these are the relative weights of the ultimate
indivisible atom, it follows that all combinations must be either atom
to atom, or one to two, three, or four; but that in no case should
combination take place in any other than a multiple proportion of the
equivalent or atomic number. This is found to be the case. Oxygen,
for instance, combines as one, two, or three atoms; its combination
presenting some multiple of its equivalent number 8, as 16, or 24:
and in like manner the combining quantity of carbon is 6, or some
multiple of that number. Where this law is not found strictly to agree
with analytical results, of which some examples are afforded by the
sesquioxides, it may be attributed, without doubt, to some error of
analysis or in the method of calculation.

Nothing can be more perfect than the manner in which nature regulates
the order of combination. We have no uncertain arrangement; but,
however great the number of the atoms of one element may be, over those
of another, those only combine which are required, according to this
great natural law, to form the compound, all the others still remaining
free and uncombined. These results certainly appear to prove that the
elementary particles of matter are not of the same specific gravities.
Do they not also indicate that any alteration in the specific gravity
of the atom would give rise to a new series of compounds, thus
apparently producing a new element? Surely there is nothing irrational
in the idea that the influences of heat or electricity, or of other
powers of which as yet we know nothing, may be sufficient to effect
such changes in the atomic constituents of this earth.

The combination of elementary atoms takes place under the influence
of an unknown force which we are compelled to express by a figurative
term, _affinity_. In some cases it would appear that the disposition
of two bodies to unite, is determined by the electrical condition; but
a closer examination of the question than it is possible to enter into
in this place, clearly shows that some physical state, not electrical,
influences combining power.

Chemical affinity or attraction is the peculiar disposition which one
body has to unite with another. To give some instances in illustration.
Water and spirit combine most readily: they have a strong affinity for
each other. Water and oil repel each other: they have no affinity;
they will not enter into combination. If carbonate of potash is added
to the spirit and water in sufficient quantity, the water is entirely
separated, and the pure spirit will float over the hydrated potash. If
potash is added to the oil and water, it combines with the oil, and,
forming soap, they all unite together; but, if we now add a little acid
to the mixture, the potash will quit the oil to combine with the acid,
and the oil will be repelled as before and float on the liquid. This
has been called single elective affinity. These elections were regarded
as constant, and chemists drew up tables for the purpose of showing the
order in which these decompositions occur.[203] Thus, ammonia, it was
shown, would separate sulphuric acid from magnesia, lime remove it from
ammonia, potash or soda from lime, and barytes from potash or soda. It
was thought the inverse of this order would not take place, but recent
researches have shown that the results are modified by quantity and
some other conditions.

It often happens that we have a compound action of this kind in which
double election is indicated. Sulphate of lime and carbonate of ammonia
in solution are brought together, and there result a carbonate of lime
and a sulphate of ammonia. Now, in such cases nothing more than single
elective attraction most probably occurs, and the carbonic acid is
seized by the lime, by the great affinity of that earth for carbonic
acid, only after it has been set free from the ammonia, and then, by
the force of cohesion acting with the combining powers, the insoluble
salt is precipitated.[204] There is a curious fact in connection with
this decomposition. If carbonate of lime and sulphate of ammonia
are mixed together dry, and exposed, in a closed vessel, to a red
heat, sulphate of lime and carbonate of ammonia are formed. These
opposite effects are not very easily explained. The action of heat is
to set free the carbonic acid; and it can only be by supposing that
considerable differences of temperature reverse the laws of affinity,
that we can at all understand this phenomenon. That different effects
result at high temperatures from those which prevail at low ones,
recent experiments prove to us, particularly those of Boutigny, already
quoted when considering decomposition by calorific action.

Under the term chemical affinity, which we regard as a power acting
at insensible distances, and producing a change in bodies, we are
content to allow ourselves to believe that we have explained the
great operations of nature. We find that the vegetable and animal
kingdoms are composed of carbon, hydrogen, oxygen, and nitrogen. The
granite mountains of the earth, and its limestone hills, and all its
other geological formations, are found to be metals and oxygen, and
carbon and sulphur, disposed to settle in harmonious union in their
proper places by chemical affinity. But what really is the power which
combines atom to atom, and unites molecule to molecule? Can we refer
the process to heat? The influence of caloric, although by changing
the form of bodies it sometimes assists combination, is to be regarded
rather as in antagonism to the power of cohesion. Can it be thought
that electricity is active in producing the result? During every change
of state, those phenomena which we term electrical are manifested; but
we thereby only prove the general diffusion of the electric principle,
and by no means show that electricity is the cause of the chemical
change. Can light determine these changes? It is evident, although
light may be a disturbing power, that it cannot be the effective one;
for many of these decompositions and recompositions are constantly
going on within the dark and silent depths of the earth, to which a
sunbeam cannot reach. That the excitation on the surface of the earth,
produced by solar influence, may modify those changes, is probable. It
is, however, certain that we must regard all manifestations of chemical
force as dependent upon some secret principles common to all matter,
diffused throughout the universe, but modified by the influences of the
known imponderable elements, and by the mechanical force of aggregative
attraction.

Bodies undergo remarkable changes of form, and present very different
characters, by reactions, which are of several kinds. We suppose
that a permanent corpuscular arrangement is maintained so long as
the equilibrium of the molecular forces is undisturbed. Water, for
instance, remains unchanged so long as the balance of affinity is kept
up between the oxygen and hydrogen of which it is composed, or so long
as the oscillations of force between these combining elements are
equal; but disturb this force, or set up a new vibratory action, as by
passing an electric current through the water, or by presenting another
body, which has the power of reacting upon one of these corpuscular
systems, and the water is decomposed, the hydrogen and oxygen gases
being set free, or one alone is liberated, and the other combined with
the molecules of the agent employed, and a new compound produced. This
is chemistry, by which science we discover all the combinations of
matter.

Having reason to conclude that atom combines with atom, according to
a system most harmoniously arranged, there can be no difficulty in
conceiving that molecule unites with molecule, in a manner regulated
by some equally well-marked law. It was, indeed, a discovery by
Wenzel, of Fribourg, that, in salts which decompose each other, the
acid which saturates one base will also saturate the other base;
and the subsequent observations of Richter, of Berlin, who attached
proportional numbers to the acids and bases, and who remarked that the
neutrality of metallic salts does not change during the precipitation
of metals by each other, which led the way to the atomic theory of Dr.
Dalton, to whom entirely belongs the observation, that the equivalent
of a compound body is the sum of the equivalents of its constituents,
and the discovery of combination in multiple proportions.

The elements of a molecule can take a new arrangement amongst
themselves, without any alteration in the number of the atoms or of
their weight, and thus give rise to a body of a different form and
colour, although possessing the same chemical constitution. This is the
case with many of the organic compounds of carbon and hydrogen.

The elements of a compound may be disassociated, and thus the
dissimilar substances of which it is composed set free. A piece
of chalk exposed to heat is, by the disturbance of its molecular
arrangement, changed in its nature; a gaseous body, carbonic acid,
is liberated, and quick-lime (oxide of calcium) is left behind. If
this carbonic acid is passed through red-hot metal tubes, or brought
in contact with heated potassium, it is resolved into oxygen and
charcoal--the oxygen combining with the metal employed. The oxide of
calcium (lime), if subjected to the action of a powerful galvanic
current, is converted into oxygen and a metal, calcium. Thus we learn
that chalk is a body consisting of two compound molecules,--carbonic
acid, which is formed by the combination of an atom of carbon with two
atoms of oxygen,--and lime, which results from the union of an atom of
calcium with one of oxygen.

The condition requisite to the production of chemical action between
bodies is that they should be dissimilar. Two elementary atoms
are placed within the spheres of each other’s influences, and a
compound molecule results. Oxygen and hydrogen form water; oxygen
and carbon give rise to carbonic acid; nitrogen and hydrogen unite
to form ammonia; and chlorine and hydrogen to produce hydrochloric
acid. In all these cases an external force is required to bring the
atoms within the range of mutual affinity: flame,--the electrical
spark,--actinism,--or the interposition of a third body, is necessary
in each case. There are other examples in which no such influence is
required. Potassium and oxygen instantly unite: chlorine, iodine, and
bromine immediately, and with much violence, combine with the metals to
form chlorides, iodides, or bromides.

With compound molecules the action is in many cases equally active,
and combination is readily effected, as in the cases of the acids and
the oxides of some metals, which are all instances of the most common
chemical attraction.

An elementary or simple molecule and molecules of a compound and
different constitution are brought together, and a new compound
results from an interchange of their atoms, whilst an element is
liberated. These are essentially illustrations of analytical chemistry.
Sulphuretted hydrogen is mixed with chlorine; the chlorine combines
with the hydrogen, and sulphur is set free. Potassium is put into
water, and it combines with the oxygen of the water, whilst the
hydrogen is liberated.

Two compound molecules being brought together may decompose each other,
and form two new compounds by an interchange of their elements.

One element may be substituted for another under certain circumstances.
Gold may be replaced by mercury; copper will take the place of silver;
and iron will occasion the separation of copper from its solutions,
the iron itself being dissolved to supply its place; chlorine will
substitute hydrogen in the carburetted hydrogen gases; and many other
examples might be adduced.

Chemical phenomena very frequently become of a complex character;
and one, two, or three of these cases may be occurring at the same
time in the decomposition of one compound by another. Such are the
general features of chemical science. Many peculiarities and remarkable
phenomena connected with chemical investigations will be named, as
the examination of the elementary composition of matter is proceeded
with; but, although the philosophy of chemical action is of the highest
interest, it must not be allowed to detain us with its details, which
are, indeed, more in accordance with a treatise on the science than
one which professes to do no more than sketch out those prevailing
and striking features which, whilst they elucidate the great truths
of nature, are capable of being employed as suggestive examples of
the tendency of scientific investigation to enlarge the boundaries of
thought, and give a greater elevation to the mind, leading us from
the merely mechanical process of analysis up to the great synthetical
operations, by which all that is found upon the earth for its ornament,
or our necessities, is created.

Among the most remarkable phenomena within the range of physical
chemistry are those of _Catalysis_, or, as it has also been called, the
“_Action of presence_.”[205] There are a certain number of bodies known
to possess the power of resolving compounds into new forms, without
undergoing any change themselves. Kirchoff discovered that the presence
of an acid, at a certain temperature, converted starch into sugar and
gum, no combination with the acid taking place. Thenard found that
manganese, platinum, gold, and silver, and, indeed, almost any solid
organic body, had the power of decomposing the binoxide of hydrogen by
their presence merely, no action being detected on these bodies. Edmund
Davy found that powdered platinum, moistened with alcohol, became
red-hot, fired the spirit, and converted it into vinegar, without
undergoing, itself, any chemical change. Döbereiner next discovered
that spongy platinum fired a current of hydrogen gas directed upon
it, which, by combining with the oxygen of the air, formed water.
Dulong and Thenard traced the same property, differing only in degree,
through iridium, osmium, palladium, gold, silver, and even glass.
Further investigation has extended the number of instances; and it has
even been found that a polished plate of platinum has the power of
condensing hydrogen and oxygen so forcibly upon its surface, that these
gases are drawn into combination and form water, with a development of
heat sufficient to ignite the metal.

This power, whatever it may be, is common in both organic and inorganic
nature, and on its important purposes Berzelius has the following
remarks:--

“This power gives rise to numerous applications in organic nature;
thus, it is only around the eyes of the potato that diastase exists:
it is by means of catalytic power that diastase, and that starch,
which are insoluble, are converted into sugar and into gum, which,
being soluble, form the sap that rises in the germs of the potato.
This evident example of the action of catalytic power in an organic
secretion, is not, probably, the only one in the animal and vegetable
kingdom, and it may hereafter be discovered that it is by an action
analogous to that of catalytic power, that the secretion of such
different bodies is produced, all which are supplied by the same
matter, the sap in plants, and the blood in animals.”[206]

It is, without doubt, to this peculiar agency that we must attribute
the abnormal actions produced in the blood of living animals by the
addition of any gaseous miasma or putrid matter, of which we have, in
all probability, a fearful example in the progress of Asiatic cholera;
therefore the study of its phenomena becomes an important part of
public hygiène.

Physical research has proved to us that all bodies have peculiar
powers, by which they condense with varying degrees of force gases
and vapours upon their surfaces; every body in nature may, indeed, be
regarded as forming its own peculiar atmosphere. To this power, in all
probability, does catalysis belong. Different views have, however,
prevailed on this subject, and Dr. Lyon Playfair[207] argues that the
catalytic force is merely a modified form of chemical affinity, exerted
under peculiar conditions.

Whatever may be the power producing chemical change, it acts in
conformity with some fixed laws, and in all its transmutations, an
obedience to a most harmonious system is apparent.

It is curious to observe the remarkable character of many of these
natural transmutations of matter, but we must content ourselves with a
few examples only. For instance:--

Sugar, oxalic acid, and citric acid are very unlike each other, yet
they are composed of the same elements; the first is used as a general
condiment, the second is a destructive poison, and the third a grateful
and healthful acid: sugar is readily converted into oxalic acid, and
in the process of ripening fruits nature herself converts citric acid
into sugar. Again, starch, sugar, and gum would scarcely be regarded
as alike, yet their only difference is in the mode in which carbon,
hydrogen, and oxygen combine. They are composed of the same principles,
in the following proportions:--

              Carbon.  Hydrogen.  Oxygen.
    Starch      12        10        10
    Sugar       12        11        11
    Gum         12        11        11

These _isomeric_ groups certainly indicate some law of affinity which
science has not yet discovered. Similar and even more remarkable
instances might be adduced of the same elements producing compounds
very unlike each other; but the above have been selected from their
well-known characters. Indeed, we may state with truth that all the
varieties of the vegetable world--their woody fibre--their acid or
alkaline juices--the various exudations of plants--their flowers,
fruit, and seeds, and the numerous products which, by art, they are
made to yield for the uses of man, are, all of them, compounds of these
three elements, differing only in the proportions in which they are
combined with nitrogen, or in some peculiar change of state in one
or other of the elementary principles. The chemist is now enabled by
simple processes, from the refuse of manufactories to produce fruit
essences which are equal in flavour to the natural production; and from
benzoic acid, which is obtained in great abundance from the houses in
which cows are kept, the most delicate essences are produced, which
are given to the world as the distillations of a thousand flowers.
By the impulse given to organic chemistry by Liebig, our knowledge
of the almost infinite variety of substances, in physical character
exceedingly dissimilar, which result from the combination of oxygen,
hydrogen, and carbon, in varying proportions, has been largely
increased. And the science is now in that state which almost causes
a regret that any new organic compounds should be discovered, until
some industrious mind has undertaken the task of reducing to a good
general classification the immense mass of valuable matter which has
been accumulated, but which, for all practical purposes, remains nearly
useless and unintelligible.

These combinations, almost infinitely varied as they are, and so
readily produced and multiplied as to be nearly at the will of the
organic analyst, are not, any of them, accidental: they are the result
of certain laws, and atom has united with atom in direct obedience
to principles which have been through all time in active operation.
They are unknown; the researches of science have not yet developed
them, and the philosopher has not yet made his deductions. They are
to be referred to some secret fixed principles of action, to a force
which has impressed upon every atom of the universe its distinguishing
character. Chemistry makes us familiar with a system of order. The
researches of analysts have proved that every body has a particular
law of combination, to which it is bound by a mathematical precision;
but it is not proportional combination alone we have to consider. If
_allotrophy_ is evidenced in the mineral world, it is certainly far
more strikingly manifested in the vegetable and animal kingdoms.

There are some cases in which bodies appear to combine without any
limitation, as spirit of wine and water, sulphuric acid and water;
but these must be considered as conditions of mixture rather than of
chemical combination.

The composition of bodies is fixed and invariable, and a compound
substance, so long as it retains its characteristic properties, must
consist of the same elements united in the same proportions. Thus,
sulphuric acid is invariably composed of 16 parts of sulphur and 24
parts of oxygen. Chalk, whether formed by nature or by the chemist,
yields 43·71 parts of carbonic acid, and 56·29 parts of lime. The rust
which forms upon the surface of iron by the action of the atmosphere,
is as invariable in its composition as if it had been formed by the
most delicate adjustment of weight by the most accurate manipulator,
being 28 parts of iron and 12 parts of oxygen. This law is the basis of
all chemical inquiry, all analytical investigations depending upon the
knowledge it affords us, that we can only produce certain undeviating
compounds as the results of our decompositions. We are not in a
position to offer any explanation which will account for these constant
quantities in combination. The forces of cohesion and elasticity
have been advanced in explanation, on the strength of the fact that
the solubility of a salt in water is regulated by cohesion, and that
of a gas by its elasticity. Although it may appear that some cases
of chemical combination are due to these powers,--as, for instance,
when the union of oxalic acid or sulphuric acid with lime produces
an insoluble salt,--we cannot thus explain the constant proportions
in which the metals, sulphur, oxygen, and similar bodies, unite. It
is quite certain there is a power or principle, which we have not
yet reached, upon which are dependent all the phenomena which we now
embrace under the term chemical affinity.

Another law teaches us that when compound bodies combine in more than
one proportion, every additional union represents a multiple of the
combining proportion of the first. With the difficulty which arises
from the sub-multiple compounds we cannot deal:--further research may
render their laws less obscure. We have seen that 8 parts of oxygen
unite with 1 of hydrogen and 14 of nitrogen. It also unites with 110 of
silver, 96 of platinum, 40 of potassium, 36 of chlorine, and 200 parts
of mercury, giving rise to--

    Water                    9
    Nitrous oxide           22
    Oxide of silver        118
    Oxide of platinum      104
    Potash                  48
    Oxide of chlorine       44
    Oxide of mercury       208

In these proportions, or in multiples of them, and in no others, will
these bodies unite with the acids or other compounds. It will, of
course, be understood that any other numbers may be adopted, provided
they stand in the same relation to each other.[208]

From the discovery of these harmonious arrangements was deduced the
beautiful atomic theory to which allusion has been already made.
Indeed, there does not appear to be any other way of explaining these
phenomena than by the hypothesis that the ultimate atoms of bodies have
_relatively_ the weights which we arbitrarily assign to them, as their
combining quantities. These views are further confirmed by the fact,
that gaseous bodies unite together by volume in very simple definite
proportions:--100 measures of hydrogen and 200 measures of oxygen form
water; 100 measures of oxygen and 100 measures of vapour of sulphur
form sulphurous acid gas. Ammoniacal gas consists of 300 volumes of
hydrogen and 100 volumes of nitrogen, condensed by combination into 200
volumes; consequently, we are enabled most readily to calculate the
specific gravity of ammoniacal gas. The specific gravity of nitrogen
is 0·9722, that of hydrogen 0·0694. Now, three volumes of hydrogen are
equal to 0·2082: this added to 0·9722 is equal to 1·1804, which is
exactly the specific gravity obtained by experiment.

There is no doubt, from the generality with which this law of volumes
prevails, that it would be found to extend through all substances,
provided they could be rendered gaseous; in other words, there is
abundant proof to convince us that throughout nature the process of
combination, in the most simple ratio of volumes, is in operation to
produce all the forms of matter known to us.

It has been shown, by the investigations of Dr. Dalton, in 1840, that
salts, containing water of crystallization, dissolve in water without
increasing the bulk of the fluid more than is due to the liquefaction
of the water which these salts contain; while Joule and Playfair
have shown that the anhydrous salts take up no space in solution.
From this we are naturally led to conclude that the volume occupied
by a salt in the solid state has a certain relation to the volume of
the same salt when in solution, and has also a fixed relation to the
volume occupied by any other salt. The law appears to be:--the atomic
volume of any salt whatever (anhydrous or hydrated) is a multiple of
11, or of a number near 11, or a multiple of 9·8 (the atomic volume
of ice), or the sum of a multiple of 11 or 9·8. Marignac, who has
also paid much attention to the subject, does not think these numbers
absolutely correct, but approximately so.[209] It would be a beautiful
exemplification of the simplicity of Nature’s operations, if it should
be clearly proved that the atomic volume of solid water (ice) regulated
the combining proportions by volume of all other bodies,--that it was
the standard by which chemical combination and ordinary solution were
determined.

In addition to the laws already indicated, there appear to be some
others of which, as yet, we have a less satisfactory knowledge, and,
as a remarkable case, we may adduce the phenomena of _substitution_,
or that power which an elementary body, under certain conditions,
possesses, of turning out one of the elements of a compound, and of
taking its place.[210] Thus, the hydrogen of a compound radical, as
carburetted hydrogen, may be replaced by chlorine, equivalent for
equivalent, and form a chloride of carbon, which being constructed
on the same type as the original, will have the same general laws of
combination.

Under the influence of these laws, all the combinations which we
discover in nature take place. The metals, and oxygen, and sulphur,
and phosphorus unite. The elements of the organic type, entering into
the closest relations, give rise to every form of vegetable life. The
acids, the gums, the resins, and the sugar which plants produce; and
those yet more complicated animal substances, bone, muscle, blood, and
bile; albumen, casein, milk, with those compounds which, under the
influence of vital power, resolve themselves into substances which are
essential to the existence, health, and beauty of the animal fabric,
are all dependent on these laws. But these metamorphoses must be
further considered in our examination of the more striking cases of
chemical action. The changes which result from organic combination are
so remarkable, and withal they show how completely the whole of the
material world is in subjection to chemical force, and every variety
of form the result of mysterious combination, that some particular
reference to these metamorphoses is demanded.

In nearly all cases of decided chemical action, all trace of the
characters of the combining bodies disappear. We say decided chemical
action, because, although sulphuric acid and water combine, and
salts dissolve in water, we may always recognize their presence, and
therefore these and similar cases cannot be regarded as strict examples
of the phenomena under consideration.

Hydrogen and oxygen, in combining, lose their gaseous forms, and are
condensed into a liquid--water. Sulphuric acid is intensely sour and
corrosive; potash is highly caustic; but united they form a salt
which is neither: they appear to have destroyed the distinguishing
characters of each other. Combined bodies frequently occupy less space
than they did previously to combination, of which numerous particular
instances might be adduced. Gases in many cases undergo a remarkable
condensation when chemically combined. In slaking lime, the water
becomes solid in the molecules of the hydrate of lime formed, and the
intense heat produced arises from the liberation of that caloric which
had been employed to keep the water liquid. When a solid passes into
the liquid state, cold is produced by the abstraction from surrounding
objects of the heat required to effect fluidity. An alteration of
temperature occurs whenever chemical change takes place, as we have
already shown, with a few trivial and uncertain exceptions. The
disturbance caused by the exercise of the force of affinity frequently
leads to the development of several physical powers.

Changes of colour commonly arise; indeed, there does not appear to be
any relation between the colour of a compound and that of its elements.
Iodine is of a deep iron-grey colour; its vapour is violet; yet it
forms beautifully white salts with the alkalies, a splendid red salt
with mercury, and a yellow one with lead. The salts of iron vary from
white and yellow to green and dark brown. Those of copper, a red metal,
are of a beautiful blue and green colour, and the anhydrous sulphate is
white.

Isomorphism, which appears in a very remarkable manner among the
organic compounds, has, under the head of crystallization, already had
our attention. There is also a class of bodies which are said to be
_isomeric_; that is, to have the same composition, although different
in their physical characters. But the idea that bodies exist, which,
although of a decidedly different external character, are of exactly
the same chemical composition and physical condition, is not tenable;
and in nearly all the examples which have been carefully examined, a
difference in the aggregate number of atoms, or in the mode in which
those atoms have respectively arranged themselves, or that peculiar
physical difference designated by the term _allotropy_, has been
detected.

Oil of turpentine and oil of lemons have the same composition, each
being composed of five equivalents of carbon and four of hydrogen.
These substances form, from the striking difference perceptible in
their external characters, a good example of isomerism.

The laws of organic chemistry are not, however, the same as those
applying to inorganic combinations. Organic chemistry is well defined
by Liebig, as the chemistry of compound radicals; and under the
influence of vitality, nature produces compounds which have all the
properties of simple elements.[211]

When we reflect upon the conditions which prevail throughout nature,
with a few of which only has science made us acquainted, we cannot fail
to be struck with the various phases of being which are presented to
our observation, and the harmonious system upon which they all appear
to depend.

When we discover that bodies are formed of certain determinate atoms,
which unite one with another, according to an arithmetical system, to
form molecules, which, combining with molecules, observe a similar law,
we see at once that all the harmonies of chemical combination--the
definite proportions, laws of volume, and the like--are but the
necessary consequences of these simple and guiding first principles.
In the pursuit of truth, investigators must discover still further
arrangements, which, from their perfection, may be compared to the
melodious interblending of sweet sounds, and many of the apparently
indeterminate combinations will, beyond a doubt, be shown to be as
definite as any others. But we cannot reflect upon the fact that these
atoms and these molecules are guided in their combinations by impulses,
which we can only explain by reference to human passions, as the term
_elective affinity_ implies, without feeling that an impenetrable
mystery of a grand and startling character in its manifestations
surrounds each grain of dust which is hurried along upon the wind.

We now, habitually, speak of attraction and repulsion--of the affinity
and non-affinity of bodies. We are disposed, from the discovery of the
attractive and repelling poles of electrified substances, to regard
these powers in all cases as depending upon some electrical state, and
we write learnedly upon the laws of these forces. After all, it would
be more honest to admit, that we know no more of the secret impulses
which regulate the combinations of matter, than did those who satisfied
themselves by referring all phenomena of these kinds to sympathies
and antipathies: terms which have a poetic meaning, conveying to the
mind, with considerable distinctness, the fact, and giving the idea
of a feeling--a passion--involving and directing inanimate matter,
similar to that which stirs the human heart, and certainly calculated
to convey the impression that there is working within all things a
living principle, and pointing, indeed, to “the soul of the world.” The
animated marble of ancient story is far less wonderful than the fact,
proved by investigation, that every atom of matter is penetrated by a
principle which directs its movements and orders its positions, and
involved by an influence which extends, without limits, to all other
atoms, and which determines their union, or otherwise.

We have gravitation, drawing all matter to a common centre, and
acting from all bodies throughout the wide regions of unmeasured
space upon all. We have cohesion, holding the particles of matter
enchained, operating only at distances too minute for the mathematician
to measure; and we have chemical attraction, different from either
of these, working no less mysteriously within absolutely insensible
distances, and, by the exercise of its occult power, giving determinate
and fixed forms to every kind of material creation.

The spiritual beings, which the poet of untutored nature gave to the
forest, to the valley, and to the mountain, to the lake, to the river,
and to the ocean, working within their secret offices, and moulding
for man the beautiful or the sublime, are but the weak creations
of a finite mind, although they have for us a charm which all men
unconsciously obey, even when they refuse to confess it. They are like
the result of the labours of the statuary, who, in his high dreams of
love and sublimated beauty, creates from the marble block a figure
of the most exquisite moulding which mimics life. It charms us for a
season; we gaze and gaze again, and its first charms vanish; it is ever
and ever still the same dead heap of chiselled stone. It has not the
power of presenting to our wearying eyes the change which life alone
enables matter to give; and we admit the excellence of the artist, but
we cease to feel at his work. The creations of poetry are pleasing, but
they never affect the mind in the way in which the poetic realities
of nature do. The sylph moistening a lily is a sweet dream; but the
thoughts which rise when first we learn that its broad and beautiful
dark-green leaves, and its pure and delicate flower, are the results
of the alchemy which changes gross particles of matter into symmetric
forms,--of a power which is unceasingly at work under the guidance of
light, heat, and electrical force,--are, after our incredulity has
passed away--for it is too wonderful for the untutored to believe at
once--of an exalting character.

The flower has grown under the impulse of principles which have
traversed to it on the solar beam, and mingled with its substance. A
stone is merely a stone to most men. But within the interstices of
the stone, and involving it like an atmosphere, are great and mighty
influences, powers which are fearful in their grander operations, and
wonderful in their gentler developments. The stone and the flower hold,
locked up in their recesses, the three great known forces--light, heat,
and electricity: and, in all probability, others of a more exalted
nature still, to which these powers are but subordinate agents. Such
are the facts of science, which, indeed, are the true “sermons in
stones,” and the most musical of “tongues in trees.” How weak are the
creations of romance, when viewed beside the discoveries of science!
One affords matter for meditation, and gives rise to thoughts of a most
ennobling character; the other excites for a moment, and leaves the
mind vacant or diseased. The former, like the atmosphere, furnishes
a constant supply of the most healthful matter; the latter gives
an unnatural stimulus, which compels a renewal of the same kind of
excitement, to maintain the continuation of its pleasurable sensations.

FOOTNOTES:

[200] All the phenomena connected with volcanic action, and the
theories connected therewith, will be found in Dr. Daubeny’s work, _A
description of active and extinct Volcanoes, of Earthquakes, and of
Thermal Springs_. 1848.

[201] Graham’s _Elements of Chemistry_. New Edition.

[202] Graham’s _Elements of Chemistry_; and Brande’s _Manual_.

[203] Of these _tables of attraction_ the following may be taken as a
specimen:--

    SULPHURIC ACID.
    Baryta.
    Strontia.
    Potassa.
    Soda.
    Lime.
    Magnesia.
    Ammonia.

It thus appears that baryta separates sulphuric acid from its compounds
with all inferior substances, and that ammonia is separated from the
acid by all that are above it.

[204] Berthollet: _Essai de Statique Chimique_, 1803. Sir Humphry Davy,
in his _Elements of Chemical Philosophy_, has given an excellent review
of the views of Berthollet.

[205] _On certain combinations of a new acid, formed of Azote, Sulphur,
and Oxygen_; by J. Pelouze. Translated from Annales de Chimie, vol.
xvi., for Scientific Memoirs, vol. i. p. 470. _Some ideas of a new
force acting in the combinations of Organic Compounds_, by Berzelius:
Annales de Chimie, vol. lxi. The conclusion come to by this eminent
chemist is expressed in the following translation:--“This new power,
hitherto unknown, is common both in organic and inorganic nature.
I do not believe that it is a power which is entirely independent
of the electro-chemical affinities of the substance. I believe, on
the contrary, that it is merely a new form of it; but so long as we
do not see their connection and mutual dependence, it will be more
convenient to describe it by a separate name. I shall, therefore, call
it _catalytic power_: I shall also call _catalysis_, the decomposition
of bodies by this force--in the same way as the decomposition of bodies
by chemical affinity is termed analysis.”

[206] Berzelius: _Annales de Chimie_, vol. lxi.

[207] _On Transformations produced by Catalytic Bodies_: by Lyon
Playfair, Esq.; Phil. Mag., vol. xxxi. p. 191, 1847.--“Facts have been
brought forward to show that there is at least as much probability in
the view that the catalytic force is merely a modified form of chemical
affinity exerted under peculiar conditions, as there is in ascribing
it to an unknown power, or to the communication of an intestine motion
to the atoms of a complex molecule. Numerous cases have been cited,
in which the action results when the assisting or catalytic body is
not in a state of change; and attempts have been made to prove, by new
experiments, that the catalytic power exercises its peculiar power by
acting in the same direction as the body decomposing, or entering into
union, but under conditions in which its own affinity cannot always be
gratified.”

[208] Consult Graham’s Chemistry, _On Combining Proportions_.

[209] _Memoir on Atomic Volume and Specific Gravity._ Messrs. Lyon
Playfair and Joule.--Philosophical Magazine, vol. xxvii. p. 453, or
Transactions of Chemical Society of London. _Observations_ on the
above, by Professor de Marignac.--Bibliothèque Universelle, Feb. 1846.
_On the Relation of the Volumes of bodies in the solid state, to their
equivalents, or atomic weights_: by Professor Otto. _Studies on the
connection between the atomic weights, crystalline form, and density
of bodies_: by M. Filhol. Translated for the Cavendish Society, and
published in their Chemical Reports and Memoirs.

[210] _Comptes Rendus de l’Académie des Sciences_, 1840, No. 5. A good
translation of Dumas’s Memoir appeared in the Philosophical Magazine,
from which I extract the following familiar exposition of the laws of
substitution:--“Let me make a comparison drawn from a familiar order of
ideas. Let us put ourselves in the place of a man overlooking a game at
chess without the slightest knowledge of the game. He would soon remark
that the pieces must be used according to positive rules. In chemistry,
the equivalents are our pieces, and the law of substitutions one of the
rules which preside over their moves. And as in the oblique move of the
pawns one pawn must be substituted for another, so in the phenomena
of substitution one element must take the place of another. But this
does not hinder the pawn from advancing without taking anything, as the
law of substitution does not hinder an element from acting on a body
without displacing or taking the place of any other element that it may
contain.”--_Memoir on the Law of Substitutions, and Theory of Chemical
Types._

[211] Liebig’s _Chemistry in its application to Agriculture and
Physiology_: translated by Lyon Playfair, Ph. D. _Animal Chemistry, or
Chemistry in its application to Physiology and Pathology_: by Justus
Liebig; translated by Wm. Gregory.

CHAPTER XII.

CHEMICAL PHENOMENA.

  Water--Its Constituents--Oxygen--Hydrogen--Peroxide
    of Hydrogen--Physical Property of Water--Ice--Sea
    Water--Chlorine--Muriatic Acid--Iodine--Bromine--Compounds
    of Hydrogen with Carbon--Combustion--Flame--Safety
    Lamp--Respiration--Animal Heat--The Atmosphere--Carbonic
    Acid--Influence of Plants on the Air--Chemical Phenomena of
    Vegetation--Compounds of Nitrogen--Mineral Kingdom, &c. &c.

Without attempting anything which shall approach even to the character
of a sketch of chemical science, we may be allowed, in our search
after exalting truths, to select such examples of the results of
combination as may serve to elucidate any of the facts connected with
natural phenomena. In doing this, by associating our examination with
well-known natural objects or conditions, the interpretation afforded
by analysis will be more evident, and the operation of the creative
forces rendered more striking and familiar, particularly if at the same
time we examine such physical conditions as are allied in action, and
are sufficiently explanatory of important features.

A large portion of this planet is covered by the waters of the ocean,
of lakes and rivers. Water forms the best means of communication
between remote parts of the earth. It is in every respect of the
utmost importance to the animal and vegetable kingdom; and, indeed, it
is indispensable in all the great phenomena of the inorganic world.
The peculiarities of saltness or freshness in water are dependent
upon its solvent powers. The waters of the ocean are saline from
holding dissolved various saline compounds, which are received in
part from, and imparted also to, the marine plants. Perfectly pure
water is without taste: even the pleasant character of freshly-drawn
spring-water is due to the admixture of atmospheric air and carbonic
acid. The manner in which water absorbs air is evidently due to a
peculiar physical attractive force, the value of which we do not at
present clearly perceive or correctly estimate. It is chemically
composed of two volumes of hydrogen gas--the lightest body known, and
at the same time a highly inflammable one--united with one volume of
oxygen, which excites combustion, and continues that action,--producing
heat and light,--with great energy. By weight, one part of hydrogen
is united with eight of oxygen, or in 100 parts of water we find 88·9
oxygen, and 11·1 of hydrogen gas. That two such bodies should unite to
furnish the most refreshing beverage, and indeed the only natural drink
for man and animals, is one of the extraordinary facts of science.
Hydrogen will not support life--we cannot breathe it and live; and
oxygen would over-stimulate the organic system, and, producing a kind
of combustion, give rise to fever in the animal frame; but, united,
they form that drink, for a drop of which the fevered monarch would
yield his diadem, and the deprivation of which is one of the most
horrid calamities that can be inflicted upon any living thing. Water
appears as the antagonist principle to fire, and the ravages of the
latter are quenched by the assuaging powers of the former; yet a
mixture of oxygen and hydrogen gases, in the exact proportion in which
they form water, explodes with the utmost violence on the contact of
flame, and, when judiciously arranged, produces the most intense degree
of heat known;--such is the remarkable difference between a merely
mechanical mixture and a chemical combination. Beyond this, we have
already noticed the remarkable fact that water deprived of air is
explosive at a comparatively low temperature, less than 300°; gunpowder
requiring a temperature of nearly 1000° F.

If we place in a globe, oxygen and hydrogen gases, in the exact
proportions in which they combine to form water, they remain without
change of state. They appear to mix intimately; and, notwithstanding
the difference in the specific gravities of the two gases, the lighter
one is diffused through the heavier in a curious manner, agreeably to
a law which has an important bearing on the conditions of atmospheric
phenomena.[212] The moment, however, that an incandescent body, or
the spark from an electric machine, is brought into contact with the
mixed gases, they ignite, explode violently, and combine to form water.
The discovery of the composition of water was thus synthetically made
by Cavendish--its constitution having been previously theoretically
announced by Watt.[213]

If, instead of combining oxygen and hydrogen in the proportions in
which they form water, we compel the hydrogen to combine with an
additional equivalent of oxygen, we have a compound possessing many
properties strikingly different from water. This--peroxide of hydrogen,
as it is called--is a colourless liquid, less volatile than water,
having a metallic taste. It is decomposed at a low temperature, and,
at the boiling point, the oxygen escapes from it with such violence,
that something like an explosion ensues. All metals, except iron, tin,
antimony, and tellurium, have a tendency to decompose this compound,
and separate it into oxygen and water. Some metals are oxidized during
the decomposition, but gold, silver, platinum, and a few others,
still retain their metallic state. If either silver, lead, mercury,
gold, platinum, manganese, or cobalt, in their highest states of
oxidation, are put into a tube, containing this peroxide of hydrogen,
its oxygen is liberated with the rapidity of an explosion, and so
much heat is excited that the tube becomes red hot. These phenomena,
to which we have already referred in noticing catalysis, are by no
means satisfactorily explained, and the peculiar bleaching property
possessed by the peroxide of hydrogen sufficiently distinguishes it
from water. There are few combinations which show more strikingly than
this the difference arising from the chemical union of an additional
atom of one element. Similar instances are numerous in the range
of chemical science; but scarcely any two exhibit such dissimilar
properties. During the ordinary processes of combustion, it has been
long known that water is formed by the combination of the hydrogen of
the burning body with the oxygen of the air. The recent researches of
Schönbein have shown that a peculiar body, which has been regarded as
a peroxide of hydrogen, to which he has given the name of OZONE, is
produced at the same time, and that it is developed in a great many
ways, particularly during electrical changes of the atmosphere. Thus
we obtain evidence that this remarkable compound, which was considered
as a chemical curiosity merely, is diffused very generally through
nature, and produced under a great variety of circumstances. During
the excitation of an electrical machine, or the passage of a galvanic
current through water by the oxidation of phosphorus, and probably
in many similar processes--in particular those of combustion, and we
may therefore infer also of respiration--this body is formed. From
observations which have been made, it would appear that, during the
night, when the activity of plants is not excited by light, they act
upon the atmosphere in such a way as to produce this ozone; and its
presence is said to be indicated by its peculiar odour during the
early hours of morning. We are not yet acquainted with this body
sufficiently to speculate on its uses in nature: without doubt, they
are important, perhaps second to those of water only. It is probable,
as we have already had occasion to remark, that ozone may be the active
agent in removing from the atmosphere those organic poisons to which
many forms of pestilence are traceable; and it is a curious fact, that
a low electrical intensity, and a consequent deficiency of atmospheric
ozone, marks the prevalence of cholera, and an excess distinguishes the
reign of influenza.[214]

Some interesting researches appear to show the probability that ozone
is simply oxygen in a state of high activity. It has been found,
indeed, that perfectly dry oxygen, which will not bleach vegetable
colours in the dark, acquires, by exposure to sunshine, the power of
destroying them. Becquerel has proved that this ozonous state may be
produced in dry oxygen by passing a succession of electric sparks
through it. Fremy passed the electric sparks on the outside of a tube
which contained perfectly dry oxygen, and it was found to have acquired
the properties of ozone. In this case, and probably in the experiments
of Becquerel, the light of the spark, rather than the electricity,
appears to have been the active agent in producing this change.
Schönbein himself does not appear disposed to regard ozone as being
either peroxide of hydrogen, or an allotropic oxygen. He leans to his
first view of its being an entirely new chemical element. The energy
of this ozone is so great, that it has been found to destroy almost
instantaneously the Indian-rubber union joints of the apparatus in
which it is formed.[215]

Water, from the consideration of which a digression has been indulged
in, to consider the curious character of one of its elements,--water is
one of the most powerful chemical agents, having a most extensive range
of affinities, entering directly into the composition of a great many
crystallizable bodies and organic compounds. In those cases where it is
not combined as water, its elements often exist in the proportions in
which water is formed. Gum, starch, and sugar, only differ from each
other in the proportions in which the elements of water are combined
with the carbon.

In saline combinations, and also in many organic forms, we must regard
the water as condensed to the solid form; that is, to exist as ice. We
well know that, by the abstraction of heat, this condition is produced;
but, in chemical combinations, this change must be the result of the
mechanical force exerted by the power of the agency directing affinity.

In the case of water passing from a liquid to a solid state, we have a
most beautiful exemplification of the perfection of natural operations.
Water conducts heat downwards but very slowly; a mass of ice will
remain undissolved but a few inches under water, on the surface of
which, ether, or any other inflammable body, is burning. If ice (solid
water) swam beneath the surface, the summer sun would scarcely have
power to thaw it; and thus our lakes and seas would be gradually
converted into solid masses at our ordinary winter temperatures.

All similar bodies contract equally during the process of cooling,
from the highest to the lowest points to which the experiments have
been carried. It has been thought that if this applied to water,
the result would be the sudden consolidation of the whole mass. A
modification of the law has been supposed to take place to suit the
peculiar circumstances of water. Nature never modifies a law for a
particular purpose; we must, therefore, seek to explain the action of
the formation of ice, as we know it, by some more rational view.

Water expands by heat, and contracts by cold; consequently, the
coldest portions of this body occupy the lower portions of the fluid;
but it must be remembered that these parts are warmed by the earth.
Ross, however, states that at the depth of 1,000 fathoms the sea
has a constant temperature of 39°. Water is said to be at its point
of greatest density at 40° of Fahrenheit’s thermometer; in cooling
further, this fluid appears to expand, in the same way as if heated:
and, consequently, water colder than this point, instead of being
heavier, is lighter, and floats on the surface of the warmer fluid.
It does not seem that any modification of the law is required to
account for this phenomenon. Water cooled to 40° still retains its
peculiar corpuscular arrangement; but immediately it passes below that
temperature, it begins to dispose itself in such a manner that visible
crystals may form the moment it reaches 32°. Now, if we conceive
the particles of water, at 39°, to arrange themselves in the manner
necessary for the assumption of the solid form, by the particular
grouping of molecules in an angular instead of a spheroidal shape,
it will be clear, from what we know of the arrangement of crystals
of water--ice--that they must occupy a larger space than when the
particles are disposed, side by side, in minute spheres. Even the
escape of air from the water in which it is dissolved is sufficient to
give an apparent lightness to the colder water. This expansion still
goes on increasing, from the same cause, during the formation of ice,
so that the specific gravity of a mass of frozen water is less than
that of water at any temperature below 40°. It must not be forgotten
that ice always contains a large quantity of air, by which it is
rendered buoyant.

Water, at rest, may be cooled many degrees below the freezing point
without becoming solid. This is easily effected in a thin glass flask;
but the moment it is agitated, it becomes a firm mass. Here we have the
indication of another cause aiding in producing crystals of ice on the
surface of water, under the influence of the disturbance produced by
the wind, which does not extend to any depth.

As oxygen and hydrogen gases enter largely into other chemical
compounds besides water, it is important to consider some of the forms
of matter into the composition of which these elements enter. To
examine this thoroughly, a complete essay on chemical philosophy would
be necessary; we must, therefore, be content with referring to a few of
the more remarkable instances.

The waters of the ocean are salt: this arises from their holding, in
solution chloride of sodium (_muriate of soda_--_common culinary salt_)
and other saline bodies. Water being present, this becomes muriate of
soda,--that is, a compound of muriatic acid and soda: muriatic acid
is hydrogen, combined with a most remarkable gaseous body, called,
from its yellow colour, _chlorine_; and soda, oxygen in union with
the metal sodium,--therefore, when anhydrous, culinary salt is truly
a chloride of sodium. Chlorine in some respects resembles oxygen; it
attacks metallic bodies with great energy; and, in many cases, produces
the most vivid incandescence, during the process of combination. It
is a powerful bleaching agent, is destructive to animal life, and
rapidly changes all organic tissues. There are two other bodies in
many respects so similar to chlorine, although one is at the ordinary
temperatures solid, and the other fluid, and which are also discovered
in sea-water, or in the plants growing in it, that it is difficult to
consider them otherwise than as different forms of the same principle.
These are iodine and bromine, and they both unite with hydrogen to
form acids. The part which chlorine performs in nature is a great and
important one. Combined in muriate of soda, we may trace it in large
quantities through the three kingdoms of nature, and the universal
employment of salt as a condiment indicates the importance to the
animal economy of the elements composing it. Iodine has been traced
through the greater number of marine plants, existing, apparently as
an essential element of their constitution; in some land plants it has
also been found, particularly in the Armeria maritima, when this plant
grows near the sea:[216] it has been detected in some mineral springs,
and in small quantities in the mineral kingdom[217] combined as iodide
of silver, and in the aluminous slate of Latorp in Sweden.[218] Bromine
is found in sea-water, although in extremely minute quantities, in a
few saline springs, and in combination with silver; but we have no
evidence to show that its uses are important in nature.

Hydrogen, again, unites with carbon in various proportions, producing
the most dissimilar compounds. The air evolved from stagnant water,
and the fire-damp of the coal mine, are both carburetted hydrogen; and
the gas which we employ so advantageously for illumination, is the
same, holding an additional quantity of carbon in suspension. Naphtha,
and a long list of organic bodies, are composed of these two chemical
elements.

These combinations lead us, naturally, to the consideration of the
great chemical phenomena of combustion, which involve, indeed, the
influences of all the physical powers. By the application of heat,
we produce an intense action in a body said to be combustible; it
burns,--a chemical action of the most energetic character is in
progress, the elements which constitute the combustible body are
decomposed, they unite with some other elementary principles, and new
compounds are formed. A body burns--it is entirely dissipated, or it
leaves a very small quantity of ashes behind unconsumed, but nothing
is lost. Its volatile parts have entered into new arrangements, the
form of the body is changed, but its constituents are still playing an
important purpose in creation.

The ancient notion that fire was an empyreal element, and the Stahlian
hypothesis of a phlogistic principle on which all the effects of
combustion depended,[219] have both given way to the philosophy of the
unfortunate Lavoisier--which has, indeed, been modified in our own
times--who showed that combustion is but the development of heat and
light under the influence of chemical combination.

Combustion was, at one period, thought to be always due to the
combination of oxygen with the body burning, but research has shown
that vivid combustion may be produced where there is no oxygen. The
oxidizable metals burn most energetically in chlorine, and some of
them in the vapour of iodine and bromine, and many other unions take
place with manifestations of incandescence. Supporters of combustion
were, until lately, regarded as bodies distinct from those undergoing
combustion. For example, hydrogen was regarded as a combustible body,
and oxygen as a supporter of combustion. Such an arrangement is a
most illogical one, since we may _burn_ oxygen in an atmosphere of
hydrogen, in the same manner as we burn hydrogen in one of oxygen; and
so, in all the other cases, the supporter of combustion may be burnt
in an atmosphere formed of the, so called, combustible. The ordinary
phenomena of combustion are, however, due to the combination of oxygen
with the body burning; therefore every instance of oxidization may be
regarded as a condition of combustion, the difference being only one of
degree.

Common iron, exposed to air and moisture, _rusts_; it combines with
oxygen. Pure iron, in a state of fine division, unites with oxygen so
eagerly, that it becomes incandescent, and in both cases oxide of iron
is formed. This last instance is certainly a case of combustion; but
in what does it differ from the first one, except in the intensity of
the action? The cases of spontaneous combustion which are continually
occurring are examples of an analogous character to the above.
Oxygen is absorbed, it enters more or less quickly, according to
atmospheric conditions, into chemical combination; heat is evolved, and
eventually,--the action continually increasing,--true combustion takes
place. In this way our cotton-ships, storehouses of flax, piles of
oiled-cloth, sawdust, &c., frequently ignite; and to such an influence
is to be attributed the destruction of two of our ships of war, a few
years since, in Devonport naval arsenal.[220]

In the economic production of heat and light, we have the combination
of hydrogen and carbon with the oxygen of common air, forming water
and carbonic acid. In our domestic fires we employ coal, which is
essentially a compound of carbon and hydrogen containing a little
oxygen and some nitrogen, with some earthy matters which must be
regarded as impurities; the taper, whether of wax or tallow, is made up
of the same bodies, differing only in their combining proportions, and,
like coal gas, these burn as carburetted hydrogen. All these bodies
are very inflammable, having a tendency to combine energetically with
oxygen at a certain elevation of temperature.

We are at a loss to know how heat can cause the combination of those
bodies. Sir Humphry Davy has shown that hydrogen will not burn, nor
a mixture of it with oxygen explode, unless directly influenced by a
body heated so as to _emit light_.[221] May we not, therefore, conclude
that the chemical action exhibited in a burning body is a development
of some latent force, with which we are unacquainted, produced by the
absorption of light;--that a repulsive action at first takes place,
by which the hydrogen and carbon are separated from each other;--and
that in the nascent state they are seized by the oxygen, and again
compelled, though in the new forms of water and carbonic acid, to
resume their chains of combining affinity?

Every equivalent of carbon and of hydrogen in the burning body unites
with two equivalents of oxygen, in strict conformity with the laws
of combination. The flame of hydrogen, if pure, gives scarcely any
light, but combined with the solid particles of carbon, it increases
in brightness. The most brilliant of the illuminating gases is the
olefiant gas, produced by the decomposition of alcohol, and it is
only hydrogen charged with carbon to the point of saturation. Flame
is a cone of heated vapour, becoming incandescent at the points of
contact with the air; a mere superficial film only being luminous. It
is evident that all the particles of the gas are in a state of very
active repulsion over the surface, since flame will not pass through
wire gauze of moderate fineness. Upon this discovery is founded the
inimitable safety-lamp of Davy, by means of which the explosive gases
of a mine are harmlessly ignited within a cage of wire gauze. This
effect has been attributed to a cooling influence of the metal; but,
since the wires may be brought to a degree of heat but little below
redness without igniting the fire-damp, this does not appear to be the
cause. The conditions of the safety lamp may be regarded as presenting
examples exactly the converse of those already stated with reference to
the spheroidal state of water; and it affords additional evidence that
the condition of bodies at high temperatures is subject to important
physical changes.

The principle upon which the safety lamp is constructed is, that a
mixture of the fire-damp and atmospheric air in certain proportions
explodes upon coming in contact with a flame.

This mixture passes readily through a wire gauze, under all
circumstances, and it, of course, thus approaches the flame of the lamp
enclosed within such a material, and it explodes. But, notwithstanding
the mechanical force with which the exploding gas is thrown back
against the bars of its cage, it cannot pass them. Consequently, the
element of destruction is caught and caged; and notwithstanding its
fierceness and energy, it cannot impart to the explosive atmosphere
without, any of its force. No combustion can be communicated through
the wire gauze.

The researches which led to the safety-lamp may be regarded as among
the most complete examples of correct inductive experiment in the range
of English science, and the result is certainly one of the proudest
achievements of physico-chemical research. By merely enveloping the
flame of a lamp with a metallic gauze, the labourer in the recesses of
the gloomy mine may feel himself secure from that outpouring current
of inflammable gas, which has been so often the minister of death; he
may walk unharmed through the explosive atmosphere, and examine the
intensity of its power, as it is wasted in trifling efforts within the
little cage he carries. Accidents have been attributed to the “Davy,”
as the lamp is called among the colliers; but they may in most cases be
traced to carelessness on the part of those whose duty it has been to
examine the lamps, or to the recklessness of the miners themselves.

That curious metal, platinum, and also palladium, possesses a property
of maintaining a slow combustion, which the discoverer of the
safety-lamp proposed to render available to a very important purpose.
If we take a coil of platinum wire, and, having made it red-hot, plunge
it into an explosive atmosphere of carburetted hydrogen and common
air, it continues to glow with considerable brightness, producing,
by this very peculiar influence, a combination of the gases, which
is discovered by the escape of pungent acid vapours. Over the little
flame of the safety-lamp, it was proposed by Davy to suspend a coil
of platinum which would be thus kept constantly at a red heat. If the
miner became accidentally enveloped in an atmosphere of fire-damp,
although the flame of his lamp might be extinguished, the wire would
continue to glow with sufficient brightness to light him from his
danger, through the dark winding passages which have been worked in the
bed of fossil fuel. This very beautiful arrangement has not, however,
been adopted by our miners.

It is thus that the discoveries of science, although they may appear
of an abstract character, constantly, sooner or later, are applied to
uses by which some branch of human labour is assisted, the necessities
of man’s condition relieved, and the amenities of life advanced.

The respiration of animals is an instance of the same kind of chemical
phenomena as we discover in ordinary combustion. In the lungs the blood
becomes charged with oxygen, derived from the atmospheric air, with
which it passes through the system, performing its important offices,
and the blood is returned to the lungs with the carbonic acid formed