and read at his leisure. The relics of hoar antiquity speaking to the
present of the past, and recording the histories of races which have
fleeted away like shadows, are thus preserved to tell their wondrous
tales.

The admirer of nature may copy her arrangements with the utmost
fidelity. Every modulation of the landscape, each projecting rock or
beetling tor--the sinuous river in its rapid flow--the meandering
stream, “gliding like happiness away;” and the spreading plains
over which are scattered the homes of honest industry and domestic
peace, intermingled with the towers of those humble temples in which
simple-hearted piety delights to “bow the head and bend their knee;”
these, all of these, may, by the sunbeam which illuminates the whole,
be faithfully pencilled upon our chemical preparations.

Our art enables us to do more even than this; we have but to present
our sensitive tablet to the moon, and she, by her own light, prints her
mountains and her valleys, and indicates with all truth the physical
conditions of her surface.

Any reference to the _chemical agency_ of LIGHT--_the luminous rays_ as
distinguished from the _chemical and calorific rays_--has been avoided
until we came to the consideration of this particular question of
chemical change.

Upon organic compounds, as, for instance, upon the colouring matter
of leaves and flowers, _light_ does exert a chemical power: and it
is found that vegetable colours are bleached, not by rays of their
own colour, but by those which are _complementary_ to them. A red dye
fades under the influence of a green ray, and a yellow under that of a
violet one, much more speedily than when exposed to rays of any other
colour; and this, it must be remembered, is due to the coloured ray
itself, and not to any _actinic_ power masked, as it were, behind the
colour, as is generally believed.[125] It was long a question whether
the decomposition of carbonic acid by plants was due to the luminous or
the chemical rays. It is now clearly established that the luminous rays
are the most active in producing this effect; which they do indirectly,
by exciting the vital powers of the organized structures. Therefore we
would refer this phenomenon of gaseous decomposition to a vital power
quickened by luminous excitement.[126]

We have already noticed some chemical phenomena due to heat,
particularly those experiments of Count Rumford’s, which appeared to
him to prove that the chemical agency of the sun’s rays was due to its
calorific power. Certain chemical phenomena, we know, may be produced
by thermic action; but the only variety of thermo-chemical action which
connects itself immediately with the solar radiations, belongs to a
class of rays to which the name of _Parathermic_ has been given, and to
which the scorching, as it is called, of plants, the browning of the
autumnal leaves, and the ripening of fruits, appear to be due.[127]
When we come to the consideration of those physical phenomena which
belong to the growth of plants, all these peculiarities of solar action
must be attended to in detail.

The manner in which we find the actinic power influencing electrical
action, also shows us that the equilibrium of forces is continued
through all the great principles of nature. If a galvanic arrangement
is made, by which small quantities of metals may be slowly precipitated
at one of the poles in the dark, and a similar arrangement be exposed
to sunshine, it will be found that no metal is deposited: the sun’s
rays have interfered with the decomposing power of the electrical
current. At the same time we learn, that by throwing a beam of light
upon a plate of copper which forms one of a galvanic pair, whilst
it is under the influence of an acidulated solution, an additional
excitation takes place, and the galvanometer will indicate the passage
of an increased current of electricity. These two dissimilar actions
appear enigmatical; but they may, there is no doubt, receive some
solution from the influence of different rays on the contrary poles
of the battery. One thing is quite evident,--electricity suffers a
disturbance of one order, by light; and an excitement of another by its
associated principles in the sunbeam. If a yellow glass is interposed
between the galvanic arrangement and the sun, the electro-chemical
precipitation goes on in the same manner as it would in perfect
darkness, and no extra excitement is produced upon the plates of the
battery. From this it would appear that actinism and not light is to be
regarded as the disturbing power.[128] It has already been shown that
yellow media possess the power of stopping back the chemical agent.

We have already, detailed many of the peculiarities of the different
varieties of Phosphori, which would seem to be the result of light.
Phosphorescence is probably excited by those rays which produce
no direct effect upon the eye. If we spread sulphuret of calcium
upon paper, and expose it to the action of the solar spectrum, it
is found to glow (in the dark) only over those spaces occupied by
the violet rays and the ordinarily dark rays beyond them; proving
that the excitation necessary to the development of the phenomena
of phosphorescence is due to a class of rays distinct from the true
light-giving principle, and more nearly allied to that principle or
power which sets up chemical decomposition. Whether the fluorescent
rays, before mentioned, which are found so abundantly over the space
which produces the greatest phosphorescent effect, are active in
producing the phenomena, is as yet an unsolved problem.

Vision and colour, calorific action, chemical change, molecular
disturbance, electrical phenomena, and phosphorescent excitation, all,
each one with a strange duality, are connected with the sunbeam.

We find, when we receive solar spectra upon iodized plates, or on
several kinds of photographic paper, that a line, over which no action
takes place, is preserved at the top and bottom of the impressed image,
and in many cases along the sides also. The only way in which this can
be accounted for, as the spectrum represents the sun in a distorted
form, is by supposing that rays come from the edges of the sun of a
different character from those which proceed from the centre of that
orb.[129]

Light from the centre of the solar disc is under different conditions
from that which comes from the edge of the sun: this is due to the
varying angle, which is presented to us by a circular body: calorific
action seems to be more strongly manifested when the envelope of
light, extending like an atmosphere to the sun, is thrown into great
agitation, and waves, and great hollows--solar spots--are produced.
There is some indication of the existence of a third condition on the
sun’s surface, to which probably belongs the mighty chemical power
which we call actinism. Electricity may be, as some have speculated,
the exciting agent; a constant and violent Aurora Borealis may exist on
the sun, and under the excitation of this force the others named may be
quickened into full activity.

That actinism is one of the great powers of creation we have abundant
proof. Nearly all the phenomena of chemical change which have been
referred to light, are now proved to be dependent upon actinic power;
and beyond the influence which has been ascertained to be exerted by
it upon all inorganic bodies, we shall have occasion to show still
further the dependence of the vegetable and animal worlds upon its
agency. The influence of the solar beams on vegetation is proved by
common experience; the closer examination of its action on vegetable
life is reserved for the chapter devoted to its phenomena. Of its
influence on animals nothing is very correctly known; but some early
experiments prove that they, like other organised bodies, are subject
to all the radiant forces, as indeed, independent of experiment, every
observation must teach. Certain it is, that organisation can take place
only where the sun’s rays can penetrate: where there is unchanging
darkness, there we find all the silence of death. Prometheus stole
fire from heaven, and gave the sacred gift to man, as the most useful
to him of all things in his necessities: by the aid of it he could
temper the severities of climate, render his food more digestible and
agreeable, and illuminate the hours of darkness. So says the beautiful
fiction of the Grecian mind,--which appears as the poetic dream or
prophetic glance of a gifted race, who felt the mysterious truth
they were yet unable to describe. Pheaton and Apollo are only other
foreshadowings of the creative energies which dwell in the glorious
centre of our universe. The poetry of the Hellenic people ascended
above the littlenesses of merely human action, and sought to interpret
the great truths of creation. Reflective, they could not but see that
some mysterious powers were at work around them; imaginative, they gave
to fine idealisations the government of those inexplicable phenomena.
Modern science has shown what vastly important offices the solar rays
execute, and that the principles discovered in a sunbeam are indeed the
exciters of organic life, and the disposers of inorganic form.

It must not be forgotten that we have already alluded to a speculation
which supposes this actinic influence to be diffused through all
nature, to be indeed the element to which chemical force in all its
forms is to be referred, and that it is merely excited by the solar
rays. This hypothesis receives some support from the very peculiar
manner in which chemical action once set up is carried on, independent
of all extraneous excitement, after the first disturbance has been
produced. If any of the salts of gold are exposed in connection with
organic matter, as on paper, to sunshine for a moment, an action is
begun, which goes on unceasingly in the dark, until the gold is reduced
to its most simple state.[130] The same thing occurs with chromate of
silver, some of the salts of mercury, argentine preparations combined
with protosulphate of iron or gallic acid, and some other chemical
combinations. These progressive influences point to some law not yet
discovered, which seems to link this radiant actinism with the chemical
agent existing in all matter.

This problem also connects itself with another class of facts which,
although due, in all probability, to a great extent, to calorific
radiations, and hence known under the general term of Thermography,
appear to involve both chemical and electrical excitation. From the
investigations of Moser and of others, we learn the very extraordinary
fact, that even inanimate masses act and react upon each other by
the influence of some dark radiations, and seem to exchange some of
the peculiarities which they possess. This appears generally in the
curious experiments which have been referred to, as confined merely
to form or structure. Thus an engraved plate will give to a polished
surface of metal or glass placed near it, after a very little time,
a neat distinct image of itself; that is, produce such a structural
disturbance as will occasion the plate to receive vapour differently
over those spaces opposite to the parts in cameo or in intaglio, from
what it does over the opposite. If a piece of wood is used instead of a
metal, there will, by similar treatment, be produced a true picture of
the wood, even to the representation of its fibres.[131]

It is also probable that chemical decomposition is produced by the
mere juxtaposition of different bodies. Iodide of gold or silver,
perfectly pure, has been placed upon a plate of glass, and a plate of
copper covered with mercury suspended over it: a gradual decomposition
of those salts is said to have been observed, iodide of mercury to
be formed, and the gold or silver salts reduced to a finely divided
metallic state.[132]

A body whose powers of radiating heat are low, being brought near
another whose radiating powers are more extensive, will, in the course
of a short time, undergo such an amount of molecular disturbance as
will effect a complete change in the arrangement of its surface, and
an impression of the body having the highest radiating powers will be
made upon the other. This impression is dormant, but may be developed
under the influence of vapour, or of oxidation.[133] A body, such
as charcoal, of low conducting power, being placed near another,
such as copper, which is a good conductor, will, in a very short
time, produce, in like manner, an impression of itself upon the metal
plate. Thus any two bodies, whose conducting or radiating powers are
dissimilar, being brought near each other, will occasion a molecular
disturbance, or impress the one with the image of the other. However
small the difference may be, an effect is perceived, and that of the
most extraordinary kind, giving rise to the production of actual images
upon each surface exposed. It is thus that a print on paper may be
copied on metal, by merely suspending it near a well-polished plate of
silver or copper for a few days. The white and black lines radiate very
differently; consequently an effect is produced on the bright metal in
the parts corresponding to the black lines, dissimilar to that which
takes place opposite to the white portions of the paper; and, on the
application of vapour, a true image of the one is found impressed upon
the other.[134]

Bodies which are in different electrical states act upon each other in
an analogous manner. Thus arsenic, which is highly electro-negative,
will, when placed near a piece of electro-positive copper, readily
impart to its surface an impression of itself, and so in like manner
will other bodies if in unlike conditions. Every substance physically
different (it signifies not whether as it regards colour, chemical
composition, mechanical structure, calorific condition, or electrical
state,) has a power of radiation by which a sensible change can be
produced in a body differently constituted.

Fable has told us that the magicians of the East possessed mirrors in
which they could at will produce images of the absent. Science now
shows us that representations quite sufficient to deceive the credulous
can be produced on the surface of polished metals without difficulty.
A highly polished plate of steel may be impressed with images of any
kind, which would remain invisible, the polished surface not being in
the least degree affected, as it regards its reflecting powers; but
by breathing over it, the dormant images would develope themselves,
and fade away again as the condensed moisture evaporated from the
surface.[135]

These, which are but a few selected from a series of results of an
equally striking character, serve to convince us that nature is
unceasingly at work, that every atom is possessed of properties by
which it influences every other atom in the universe, and that a most
important class of natural phenomena appear to connect themselves
directly with the radiant forces.

The alchemists observed that a change took place in chloride of silver
exposed to sunshine. Wedgwood first took advantage of that discovery to
copy pictures. Niepce pursued a physical investigation of the curious
change, and found that all bodies were influenced by this principle
radiated from the sun. Daguerre produced effects from the solar pencil
which no artist could approach to; and Talbot and others extended the
application. Herschel took up the inquiry; and he, with his usual
power of inductive search and of philosophical deduction, presented
the world with a class of discoveries which showed how vast a field of
investigation was opening for the younger races of mankind,--a field
in which a true spirit may reap the highest reward in the discovery of
new facts, and to which we must look for a further development of those
great powers with which we have already some slight acquaintance, and
for the discovery of higher influences which are not yet dreamed of in
our philosophy.

    If music, with its mysteries of sound,
      Gives to the human heart a heavenward feeling;
    The beauty and the grandeur which are found
    Spread like a vesture this fair earth around,
      Creation’s wond’rous harmonies revealing,
      And to the soul in truth’s strong tongue appealing,
    With all the magic of those secret powers,
      Which, mingling with the lovely band of light,
    The sun in constant undulation showers
    To mould the crystals, and to shape the flowers,
      Or give to matter the immortal might
    Of an embracing soul--should, from this sod,
    Exalt our aspirations all to God.

FOOTNOTES:

[117] See _Researches on Light_, by the Author.--Reference to any of
the works of the alchemists will prove the prevalence of the idea
expressed in the text. We find that gold was considered to be always
under the influence of light and solar heat.--“It is said of gold that
it waxeth cold towards daylight, insomuch that they who wear rings of
it may perceive when the day is ready to dawn.”--_Speculum Mundi, or a
Glass representing the face of the World_. Cambridge, 1643.

[118] Daguerre’s Report to the Academy of Sciences: _La Daguerréotype
Historique, et description des procédés du Daguerréotype et du Diorama_
(Paris, 1839); particularly the description of _Heliography_, by M.
Niepce. See also the letters by Niepce, published for the first time in
_Researches on Light_.

[119] “If a solution of peroxalate of iron be kept in a dark place,
or if it be exposed to 212° of Fahr. for several hours, it does not
undergo any sensible change in its physical properties, nor does it
exhibit any phenomenon which may be considered as the result of any
elementary action.

“If, however, it be exposed to the influence of solar light in a glass
vessel provided with a tube, the concentrated solution of oxalate
of iron soon presents a very interesting phenomenon: in a short
time the solution receiving the solar rays, developes an infinite
number of bubbles of gas, which rise in the liquor with increasing
rapidity, and give the solution the appearance of a syrup undergoing
strong fermentation. This ebullition always becomes stronger, and
almost tumultuous, when an unpolished glass tube is immersed in it
with a small piece of wood; the liquid itself is afterwards thrown
into ascending and descending currents, becomes gradually yellowish,
turbid, and eventually precipitates protoxalate of iron, in the form
of small brilliant crystals of a lemon-yellow colour, gas continuing
to evolve.” _Chemical action of light, and formation of Humboldtine
by it_; Phil. Mag., 1832, second series.--“When a solution of
platinum in nitro-muriatic acid, in which the excess of acid has been
neutralized by the addition of lime, and which has been well cleared
by filtration, is mixed with lime-water in the dark, no precipitation
to any considerable extent takes place for a long while,--indeed, none
whatever, though after very long standing a slight flocky sediment
is formed, after which the action is arrested entirely. But if the
mixture, either freshly made or when cleared by subsidence of this
sediment, is exposed to sunshine, it instantly becomes milky, and a
copious formation of a white precipitate (or a pale yellow one, if the
platinic solution be in excess) takes place, which subsides quickly
and is easily collected. The same takes place more slowly in cloudy
daylight.”--_On the action of light in determining the precipitation of
Muriate of Platinum by Lime water_; being an extract from a letter from
Sir John F. W. Herschel, K.H., F.R.S., &c., to Dr. Daubeny.--Phil. Mag.
1832.

[120] _On a change produced by Exposure to the Beams of the Sun, in
the properties of an elementary substance_, by Professor Draper;
_On the changes which bodies undergo in the dark_, by Robert Hunt:
Report of the Thirteenth Meeting of the British Association, vol.
xii,--_Description of the Tithonometer, an instrument for measuring
the chemical force of the Indigo-tithonic rays_: by J. W. Draper,
M.D.--Philosophical Magazine, Dec. 1843, vol. xxiii.

[121] For several illustrations of this remarkable phenomenon, see _On
the Action of the Rays of the Solar Spectrum on Vegetable Colours,
and on some new Photographic Processes_; by Sir John F. W. Herschel,
Bart., K.H., F.R.S.--Phil. Trans. June, 1842, vol. cxxxiii.; _On
certain improvements on Photographic Processes described in a former
communication, and on the Parathermic Rays of the Solar Spectrum_;
by Sir John F. W. Herschel, Bart., K.H., F.R.S., &c., in a letter
addressed to S. Hunter Christie.--Phil. Trans. 1843, vol. cxxxiv.

[122] Sir J. F. W. Herschel; see also _Researches on Light_, by the
Author.

[123] Attention has been directed to the protecting action of certain
rays of the spectrum by Sir John Herschel and others. See the
Eighteenth Report of the British Association for an experiment by
the Author, in which it was proved that all the LIGHT rays protected
photographic papers from chemical change, and, therefore, convincingly
show that light and actinism were not similar powers.

[124] “Having noticed, one densely foggy day, that the disc of the sun
was of a deep red colour, I directed my apparatus towards it. After
ten seconds of exposure, I put the prepared plate in the mercury box,
and I obtained a round image perfectly black;--the sun had produced no
photogenic effect. In another experiment, I left the plate operating
for twenty minutes; the sun had passed over a certain space of the
plate, and there resulted an image seven or eight times the sun’s
diameter in length; it was black throughout, so that it was evident,
wherever the red disc of the sun had passed, not only was there a
want of photogenic action, but the red rays had destroyed the effect
produced previous to the sun’s passage. I repeated these experiments
during several days successively, operating with a sun of different
tints of red and yellow. These different tints produced nearly the same
effect; wherever the sun had passed, there existed a black band.”--Mr.
Claudet, _On different properties of Solar Radiation, modified by
coloured glass media, &c._: Phil. Trans. 1847. Part 2.

[125] “It may also be observed that the rays effective in destroying
a given tint are, in a great many cases, those whose union produces a
colour complementary to the tint destroyed, or at least one belonging
to that class of colours to which such complementary tint may be
referred. For example, yellows tending towards orange are destroyed
with more energy by the blue rays; blue by the red, orange, and yellow
rays; purples and pinks by yellow and green rays.”--Sir J. F. W.
Herschel, _On the action of the rays of the Solar Spectrum on Vegetable
Colours_: Phil. Trans., vol. cxxxiii. 1842.

[126] The following memoirs and works are necessary to a complete
history of the inquiry:--_Experiments and observations relating
to various branches of natural philosophy, with a continuation of
the observation on air_: by Dr. Priestley. London, 1779. _Mémoires
Physico-chimiques, &c._: by J. Senebier. _Expériences sur les
végétaux_, by De la Ville: Paris, 1782; and Phil. Trans. 1782.
_Observations sur les expériences de M. Ingenhousz_: by De la Ville;
Roz. obs. 23, 290. _Expériences propres à développer les effets de la
lumière sur certaines plantes_: by Tessier; Mém. de l’Ac. des Sc. de
Paris, 1783, p. 132; Licht. Mag. iv. 4, 146. _Sur la vertu de l’eau
impregnée d’air fixe pour en obtenir, par le moyen des plantes et de
la lumière du soleil, de l’air déphlogistiqué_: by Ingenhousz; Roz.
obs. 24, 337. _Expériences sur l’action de la lumière solaire dans la
végétation_: by Senebier; Genève et Paris, 1788, p. 61. _Extrait des
expériences de M. Senebier sur l’action de la lumière solaire dans la
végétation_: by Hasenfratz; Ann. Chim. iii. 2nd. ser. 266. _Expériences
relatives à l’influence de la lumière sur quelques végétaux_: by De
Candolle; Jour. de Ph. lii. 124: Voigt’s Mag. ii. 483; Gilb. Ann.
xiii. 372; Mém. des Sav. Etr. i. 329. _Recherches chimiques sur la
végétation_: by Saussure; Ann. Chim. l. 225; Jour. de Ph. lvii. p.
393; Gilb. Ann. xviii 208. _Recherches sur la respiration des plantes
exposées à la lumière du soleil_; by Ruhland; Ann. Ch. Ph. iii. 411;
Jour. de Ph. 1816. _On the action of light upon plants, and of plants
upon the atmosphere_: by Dr. Daubeny; Phil. Trans. cxxvii January,
1836. _On the action of yellow light in producing the green colour, and
of indigo light on the movements of plants_: by P. Gardner; Phil. Mag.
xxiv.; Bibl. Univ. xlix. p. 376, and lii. p. 381. _On the influence of
light on plants_: by R. Hunt; Phil. Mag. xxiv. p. 96; Bibl. Univ. xlix.
p. 383; Athen. 1844. _Note on the decomposition of carbonic acid by
the leaves of plants, under the influence of yellow light_: by Draper;
Phil. Mag. xxv. p. 169. _On the action of the yellow rays of light on
vegetation_: by Harkness; Phil. Mag. xxv. p. 339. _Influence des rayons
solaires sur la végétation_: by Zantedeschi; Inst. No. 541, p. 157.

[127] Sir John Herschel’s Memoirs already referred to; and _Reports on
the influence of the Solar Rays on the growth of Plants_, by Robert
Hunt: Report of the British Association for the Advancement of Science,
for 1847.

[128] _Memoir on the Constitution of the Solar Spectrum_, presented at
the meeting of the Academy of Sciences, 1842, by M. Edmond Becquerel;
_Des effets produits sur les corps par les rayons solaires_, par M.
Edmond Becquerel, aide au Muséum d’Histoire Naturelle: Mémoire présenté
à l’Académie des Sciences, le 23 Octobre, 1843.--“Dans le courant de
ce mémoire, j’ai employé les noms de rayons lumineux, chimiques, et
phosphorogéniques, pour désigner, dans chaque cas, la portion des
rayons solaires qui agit pour produire, en particulier, les effets
lumineux, chimiques, et phosphorogéniques; mais cela est sans préjudice
de l’opinion que je viens d’émettre touchant l’existence d’un seul et
même rayonnement.”

“My reply is this,” says M. Arago, in his paper entitled
_Considerations relative to the action of Light_: “It is by no means
proved that the photogenic modifications of sensitive substances
result from the action of the solar light itself. The modifications
are, perhaps, engendered by invisible radiations mixed with light
properly so called, proceeding with it, and being similarly refracted.
In this case, the experiment would prove not only that the spectrum
formed by these invisible rays is not continuous, that there are
solutions of continuity as in the visible spectrum, but also that in
the two superposed spectra these solutions correspond exactly. This
would be one of the most curious, one of the most strange results of
physics.”--Taylor’s Scientific Memoirs.

[129] The chemical evidence of this will be found in Sir John
Herschel’s Memoir _On the Solar Spectrum_, and particularly as
exemplified in the changes produced on the tartrate of silver. Similar
influences are described as observed on a Daguerreotype plate, in
a paper entitled _Experiments and Observations on Light which has
permeated coloured media, and on the Chemical Action of the Solar
Spectrum_; by Robert Hunt.--Philosophical Magazine, vol. xxvi. 1840.

[130] This peculiar continuance of an effect has frequently been
observed in many of the photographic processes. In a note to a memoir
_On certain improvements in Photographic processes_, Sir John Herschel
thus refers to this property:--“The excitement is produced on such
paper by the ordinary moisture of the atmosphere, and goes on slowly
working its effect in the dark, apparently without other limit than is
afforded by the supply of ingredients present. In the case of silver it
ultimately produces a perfect _silvering_ of all the sunned portions.
Very singular and beautiful photographs, having much resemblance to
Daguerreotype pictures, are thus produced; the negative character
changing by keeping, and by quite insensible gradations to positive,
and the shades exhibiting a most singular _chatoyant_ change of colour
from ruddy-brown to black, when held more or less obliquely. No doubt,
also, gold pictures with the metallic lustre might be obtained by the
same process, though I have not tried the experiment.”

[131] The details of this curious subject may be studied in the
following memoir and communications:--_On vision and the action of
light on all bodies_: by Professor Ludwig Moser, of Königsberg; from
Poggendorff’s Annalen, vol. lvi. p. 177, No. 6, 1845. _Some remarks
on Invisible Light_: by Professor Ludwig Moser, of Königsberg; from
Poggendorff’s Annalen, vol. lvi. p. 569, No. 8. _On the power which
light possesses of becoming latent_: by Professor Ludwig Moser, of
Königsberg; from Poggendorff’s Annalen, vol. lvii. No. 9, p. 1. 1842.
_On certain spectral appearances, and on the discovery of latent
light_: by J. W. Draper, M.D., Professor of Chemistry in the University
of New York; Phil. Mag. p. 348, Nov. 1842. _On a new imponderable
substance, and on a class of chemical rays analogous to the rays of
dark heat_: by Professor Draper; Phil. Mag., Dec. 1842. _On the action
of the rays of the solar spectrum on the Daguerreotype plate_; by Sir
J. F. W. Herschel, Bart.; Phil. Mag., Feb. 1843. See remarks in this
paper on the use which Moser has made of coloured glasses: also a
communication by Professor Draper, _On the rapid Detithonizing power of
certain gases and vapours, and on an instantaneous means of producing
spectral appearances_: Phil. Mag., March 1843; and _On the causes which
concur in the production of the images of Moser_: Comptes Rendus, Nov.
1842. See _Scientific Memoirs_, vol. iii.

[132] This fact was first observed by myself, and described in the
paper already referred to, Philosophical Magazine, vol. xxii. p. 270.
It does not, however, appear to have attracted the attention of any
other observer.

[133] _On Thermography, or the Art of copying Engravings or any printed
characters from paper or plates of metal, and on the recent discovery
of Moser, relative to the formation of images in the dark_, by Robert
Hunt: Reports of the Royal Cornwall Polytechnic Society for 1842, and
Philosophical Magazine, vol. xxi. p. 462.--_On the Spectral Images of
M. Moser_, by Robert Hunt: Philosophical Magazine, vol. xxiii. p. 415.

[134] _Catalytic force, or attraction of surface concerned in the
diffusive power of gases: an occult energy or power in saturated saline
solutions_; Prater.--Mechanic’s Magazine, vol. xlv. p. 106. _Ueber
elektrische Abbildungen_; by G. Karsten.--Poggendorff’s Annalen, vol.
lvii. p. 402.--Melloni and Brewster may be consulted for much that is
most remarkable connected with radiation from coloured surfaces.

[135] Cornelius Agrippa is said to have possessed such a mirror.
The Chinese make mirrors which, when placed in a particular light,
show upon their polished faces the pattern on the back of the metal,
although it is invisible in every other position. This is effected by
giving different degrees of hardness to the various parts of the metal.
In _Natural Magic_, by Sir David Brewster, several curious experiments
belonging to this class are named.

CHAPTER IX.

ELECTRICITY.

  Discovery of Electrical Force--Diffused through all Matter--What
    is Electricity?--Theories--Frictional Electricity--Conducting
    Power of Bodies--Hypothesis of two Fluids--Electrical
    Images--Galvanic Electricity--Effects on Animals--Chemistry of
    Galvanic Battery--Electricity of a Drop of Water--Electro-chemical
    Action--Electrical Currents--Thermo-Electricity--Animal
    Electricity--Gymnotus--Torpedo--Atmospheric Electricity--Lightning
    Conductors--Earth’s Magnetism due to Electrical Currents--Influence
    on Vitality--Animal and Vegetable Development--Terrestrial
    Currents--Electricity of Mineral Veins--Electrotype--Influence of
    Heat, Light, and Actinism on Electrical Phenomena.

If a piece of amber, _electrum_, is briskly rubbed, it acquires the
property of attracting light bodies. This curious power excited the
attention of Thales of Miletus; and from the investigations of this
Grecian philosopher we must date our knowledge of one of the most
important of the natural forces--Electricity.

If an inquiring mind had not been led to ask why does this curious
natural production attract a feather, the present age, in all
probability, would not have been in possession of the means by which it
is enabled to transmit intelligence with a rapidity which equals the
poet’s dream of the “swift-winged messengers of thought.” To this age
of application a striking lesson does this amber teach. Modern utility
would have regarded Thales as a madman. Holding a piece of yellow
resin in his hand, rubbing it, and then picking up bits of down, or
catching floating feathers, the old Greek would have appeared a very
imbecile, and the _cui bono_ generation would have laughed at his silly
labours. But when he announced to his school that this amber held a
soul or essence, which was awakened by friction, and went forth from
the body in which it previously lay dormant, and brought back the small
particles floating around it, he gave to the world the first hint of
a great truth which has advanced our knowledge of physical phenomena
in a marvellous manner, and ministered to the refinements and to the
necessities of civilisation. Each phenomenon which presents itself to
us, however simple it may appear to be, is an outward expression of
some internal truth, the interpretation of which is only to be arrived
at by assiduous study, but which, once discovered, directs the way to
new knowledge, and gives to man a great increase of power. There is no
truth so abstract that it will not find its useful application, and
every example of the ministration of Physical Science to the purposes
of humanity is an evidence of the value of abstract study, and a reply
to the utilitarian in his own language.

Electricity appears to be diffused through all nature; and it is,
beyond all doubt, one of the most important of the physical forces, in
the great phenomena of creation. In the thunder-cloud, swelling with
destruction, it resides, ready to launch its darts and shake the earth
with its explosions: in the aërial undulations, silent and unseen, it
passes, giving the necessary excitement to the organisms around which
it floats. The rain-drop--the earth-girdling ocean--and the ringing
waters of the hill-born river, hold locked this mighty force. The
solid rocks--the tenacious clays which rest upon them--the superficial
soils--and the incoherent sands, give us evidence of the presence of
this agency; and in the organic world, whether animal or vegetable, the
excitement of electrical force is always to be detected.

In the solar radiations we have perhaps the prime mover of this
power. In our atmosphere, when calm and cloudless, a great ocean of
light, or when sombre with the mighty aspect of the dire tornado, we
can constantly detect the struggle between the elements of matter to
maintain an equilibrium of electrical force.

Diffused throughout matter, electricity is ever active; but it must
be remembered that although it is evidently a necessary agent in all
the operations of nature, that it is not the agent to which everything
unknown is to be referred. Doubtless the influence of this force is
more extensive than we have yet discovered; but that is an indolent
philosophy which refers, without examination, every mysterious
phenomenon to the influence of electricity.

The question, what is electricity? has ever perplexed, and still
continues to agitate, the world of science. While one set of
experimentalists have endeavoured to explain the phenomena they have
witnessed, upon the theory that electricity is a peculiar subtile
fluid pervading matter, and possessing singular powers of attraction
and repulsion, another party find themselves compelled to regard
the phenomena as giving evidence of the action of two fluids which
are always in opposite states; while again, electricity has been
considered by others as, like the attraction of gravitation, a mere
property of matter.[136] Certain it is, that in the manifestations
of electrical phenomena we have, as it appears, the evidence of two
conditions of force; but of the states of _positive_ or _negative_, of
_vitreous_ or _resinous_ electricity, we have a familiar explanation
in the assumption of some current flowing into or out of the material
body,--of some principle which is ever active in maintaining its
equilibrium, which, consequently, must act in two directions, and
always exhibit that duality which is a striking characteristic of this
subtile agent. It is a curious, and it should be an instructive fact,
that each of the three theories of electricity is capable of proof,
and has, indeed, been most ably supported by the rigorous analysis
of mathematics. When we remember that some of the most enlightened
investigators of this and the past age have severally maintained,
in the most able manner, these dissimilar views, we should hesitate
before we pronounce an opinion upon the cause or causes of the very
complicated phenomena of electrical force.

Although we discover, in all the processes of nature, the
manifestations of this principle or force in its characteristic
conditions, it will be necessary, before we regard the great phenomena,
to examine the known sources from which we can most readily evoke the
mighty power of electricity. If we rub a piece of glass or resin, we
readily render this agent active; these substances appear, by this
excitement, to become surrounded by an attractive or a repellent
atmosphere. Let us rub a strip of writing paper with Indian rubber,
or a strip of Gutta Percha with the fingers, in the dark, and we have
the manifestation of several curious phenomena. We have a peculiar
attracting power; we have a luminous discharge in the shape of a spark;
and we have very sensible evidence of muscular disturbance produced by
applying the knuckle to the surface of the material. In each case we
have the development of the same power.

Every substance in nature is an electric, and, if so disposed that its
electricity may not fly off as it is developed, we may, by friction,
manifest its presence, and, indeed, measure its quantity or its force.
All bodies are not, however, equally good electrics; shell-lac, amber,
resins, sulphur, and glass, exhibiting more powerfully the phenomena
of frictional or mechanical electricity, than the metals, charcoal,
or plumbago. Solid bodies allow this peculiar principle to pass along
them also in very different degrees. Thus electricity travels readily
through copper and most other metals, platinum being the worst metallic
conductor. It also passes through living animals and vegetables, smoke,
vapour, rarified air, and moist earth; but it is obstructed by resins
and glass, paper when dry, oils, and dry metallic oxides, and in a very
powerful manner by Gutta Percha.[137]

If, therefore, we place an electric upon any of those non-conducting
bodies, the air around being well dried, we are enabled to gather
a large quantity of the force for the production of any particular
effect. Taking advantage of this fact, arrangements are made for the
accumulation and liberation at pleasure of any amount of electricity.

A Leyden phial,--so called from its inventor, Musschenbroek, having
resided at Leyden,--is merely a glass bottle lined within and without,
to within a few inches of the top, with a metal coating. If a wire or
chain, carrying an electric current, is allowed to dip to the bottom
of the bottle, the inner coat of the jar becomes charged, or gathers
an excess, whilst the outer one is in its natural condition--one is
said to be in a _positive_, and the other in a _negative_ state. If
the two coatings are now connected by a good conductor, as a piece of
copper wire, passing from one to the other, the outside to the inside,
a discharge, arising from the establishment of the equilibrium of the
two coatings, takes place; and, if the connection is made through the
medium of our bodies, we are sensible of a severe disturbance of the
nervous system.

The cause of the conducting and non-conducting powers of bodies we know
not; they bear some relation to their conducting powers for caloric;
but they are not in exact obedience to the same laws. When we consider
that resin, a comparatively soft body, in which, consequently,
cohesive attraction is not very strong, is an imperfect conductor,
and that copper, in which cohesion is much more powerful, is a good
conductor, we may be disposed to consider that it is regulated by the
closer approximation of the particles of matter. But in platinum the
corpuscular arrangement must be much more dense than it is in copper,
and yet it is, compared with it, a very bad conductor.[138]

We have now learnt that we may, by friction, excite the electricity
in a vitreous substance; but it must not be forgotten that we cannot
increase the quantity which is, under ordinary conditions, natural to
the electric; to do so, we must in some way establish a channel of
communication with the earth, from which, through the medium we excite,
we draw our supply. We have the means of confining this mighty force
within certain limits of quantity and of time. If we place bodies which
are susceptible of electrical excitation in a sensible degree upon
insulating ones, we may retain for a considerable time the evidences of
the excitement, in the same way as with the Leyden jar; but there is a
constant effort to maintain a balance of conditions, and the body in
which we have accumulated any extraordinary quantity by conduction soon
returns to its natural state.

A very simple means may be adopted of showing what is thought to be
one of the many evidences in favour of two electricities. If the
wire carrying the current flowing from the machine, is passed over
paper covered with nitrate of silver, it produces no change upon it;
but if the wire which conveys the current to the instrument, when
it is excited, is passed over the same paper, the silver salt is
decomposed.[139] We may, however, explain this result in a satisfactory
manner, upon the hypothesis that the decomposition is produced by the
abstraction of electricity, rather than by any physical difference in
the fluid itself. By frictional electricity we may produce curious
molecular disturbances, and give rise to molecular re-arrangements,
which have been called “electrical images,” in glass, in stone, and in
the apparently less tractable metals: these images are rendered visible
by the manner in which, according to their electrical states, some
lines receive any particular powder, or vapour, which is repelled from
other spaces. Many of the great natural phenomena, such as Lightning
and Thunder, the Aurora Borealis, and Meteors, may be imitated in a
curiously exact manner by the electrical machine and a few familiar
arrangements.[140]

Voltaic electricity, as the active force produced by chemical change
is commonly called, in honour of the illustrious Volta, is now to
be considered. It differs from frictional electricity in this:--the
electricity developed by friction of the glass plate or cylinder of
the electrical machine is a discharge with a sort of explosion. It
is electricity suddenly liberated from the highest state of tension,
whereas that which is generated by chemical action in the voltaic
battery is a steady flowing current. We may compare one to the ignition
of a mass of gunpowder at once, and the other to the slow burning of
the same quantity spread out into a very prolonged train.

There are numerous ways in which we may excite the phenomena of
Voltaism, but in all of them the decomposition of one of the elements
employed appears to be necessary. This is the case in the arrangements
of batteries in which two dissimilar metals, zinc and copper, silver
and platinum, or the like, is immersed in fluids; the zinc or the
silver are gradually converted into soluble salts, which are dissolved,
whilst the copper or platinum is protected from any action. The most
simple manner of illustrating the development of this electricity is by
placing a piece of silver on the tongue, and a piece of zinc or lead
underneath it. No effect will be observed so long as the two metals
are kept asunder, but when their edges are brought together, a slight
tremulous sensation will pass through the tongue, a saline taste be
distinguished by the palate, and if in the dark, light will be observed
by the eye.

This, the germ of the most remarkable of the sciences, was noticed by
Sulzar, fifty years before Galvani observed the convulsions in the
limbs of frogs, when excited by the action of dissimilar metals; but
the former paid little attention to the phenomenon, and the discovery
led to no results.

When Galvani’s observant mind was directed to the remarkable fact that
the mere contact of two dissimilar metals with the moist surface of
living muscles produced convulsions, there was an awakening in the soul
of that philosopher to a great fundamental truth, which was nurtured
by him, tried and tested, and preserved to work its marvels for future
ages.

Although the world of science looks back to Volta as the man who gave
the first true interpretation of this discovery, yet the ordinary world
will never disconnect this important branch of physical science from
the name of Galvani, and chemical electricity in all its forms will for
ever be known under the familiar name of Galvanism. And it must not be
forgotten, that the phenomena of the manifestation of electricity, in
connection with the conditions of vitality, are entirely due to Galvani.

Let us examine the phenomena of Galvanism in its most simple phases:--

If we place a live flounder upon a plate of zinc, put a shilling on its
back, and then touch both metals with the ends of a metallic wire, the
fish will exhibit painful convulsions. The zinc becomes oxidized by
the separation of oxygen from the fluid on the surface with which it is
in contact, whilst hydrogen gas is liberated at that surface touched
by the other metal. Here we have, in the first place, a chemical
change effected, then a peculiar muscular disturbance. Each successive
combination or decomposition, like a pulsation, is transmitted along
the circuit from one extremity to the other. How the impulse which is
derived from the zinc is transmitted through the body of the animal, or
the tongue, to the silver or copper is the next consideration.

We can only understand this upon the supposition that a series of
impulses are communicated in the most rapid manner along the connecting
line; the idea of a current, although the term is commonly employed,
tends to convey an imperfect impression to the mind. It would seem
rather that a disturbance throughout the entire circuit is at once set
up by a series of vibrations or impulses communicated from particle to
particle, and along the strange net-work of nerves. One set of chemical
elements have a tendency to develope themselves at that point where
vibration is first communicated to the mass from a better conductor
than it is, and another set at the point where it passes from the
body to a better conductor than itself. The cause of this is to be
sought for in the laws which regulate molecular constitution--by which
chemical affinity is disturbed,--and a new attractive force exerted,
in obedience to which the vital energy is itself agitated. We must
not, however, forget that it is probable after all, although not yet
susceptible of proof, that the electricity does nothing more than
disturb or quicken the unknown principles upon which chemical and vital
phenomena depend; being, indeed, a secondary agent.[141]

Notwithstanding our long acquaintance with the phenomena of galvanism,
there are but few who entertain a correct idea of the enormous amount
of electricity which is necessary to the existing conditions of matter.
To Faraday we are indebted for the first clear set of deductions from a
series of inductive researches, which are of the most complete order.
He has proved, by a series of exceedingly conclusive experiments, that
if the electrical power which holds a grain of water in combination,
or which causes a grain of oxygen and hydrogen to unite in the right
proportions to form water, could be collected and thrown into the
condition of a voltaic current, it would be exactly the quantity
required to produce the decomposition of that grain of water, or the
liberation of its elements, hydrogen and oxygen.[142]

By direct experiment it has been proved that one equivalent of zinc in
a voltaic arrangement evolves such a quantity of electricity in the
form of a current, as, passing through water, will decompose exactly
one equivalent of that fluid. The law has been thus expressed:--The
electricity which decomposes, and that which is evolved by the
decomposition of a certain quantity of matter, are alike. The
equivalent weights of bodies are those quantities of them which contain
equal quantities of electricity; electricity determining the equivalent
number, because it determines the combining force.[143]

The same elegant and correct experimentalist has shown that zinc and
platinum wires, one-eighteenth of an inch in diameter, and about half
an inch long, dipped into water in which is mixed sulphuric acid so
weak that it is not sensibly sour to the tongue, will evolve more
electricity in one-twentieth of a minute than is given by thirty turns
of a large and powerful plate electrical machine in full action, a
quantity which, if passed through the head of a cat, is sufficient to
kill it as by a flash of lightning. Pursuing this interesting inquiry
yet further, it is found that a single grain of water contains as
much electricity as could be accumulated in 800,000 Leyden jars, each
requiring thirty turns of the large machine of the Royal Institution to
charge it,--a quantity equal to that which is developed from a charged
thunder-cloud. “Yet we have it under perfect command,--can evolve,
direct, and employ it at pleasure; and when it has performed its full
work of electrolisation, it has only separated the elements of a single
grain of water.”

It has been argued by many that the realities of science will not admit
of anything like a poetic view without degrading its high office; that
poetry, being the imaginative side of nature, has nothing in common
with the facts of experimental research, or with the philosophy which
generalises the discoveries of severe induction. If our science was
perfect, and laid bare to our senses all the secrets of the inner
world; if our philosophy was infallible, and always connected one
fact with another through a long series up to the undoubted cause of
all--then poetry, in the sense we now use the term, would have little
business with the truth; it would, indeed, be lost or embodied, like
the stars of heaven, in the brightness of a meridian sun. But to take
our present fact as an example, how important a foundation does it
offer upon which to build a series of thoughts, capable of lifting
the human mind above the materialities by which it is surrounded,--of
exalting each common nature by the refinement of its fresh ideas to a
point higher in the scale of intelligence,--of quickening every impulse
of the soul,--and of giving to mankind the most holy longings.

What does science tell us of the drop of water? Two gases, the one
exciting life and quickening combustion, the other a highly inflammable
air, are, by the influence of a combination of powers, brought into
a liquid globe. We can, from this crystal sphere, evoke heat, light,
electricity, and actinism in enormous quantities; and beyond these
we can see powers or forces, for which, in the poverty of our ideas
and our words, we have not names; and we learn that each one of these
principles is engaged in maintaining the conditions of the drop of
water which refreshes organic nature, and gives gladness to man’s
dwelling-place.

Has poetry a nobler theme than this? Agencies are seen like winged
spirits of infinite power, each one working in its own peculiar way,
and all to a common end,--to produce, under the guidance of omnipotent
rule, the waters of the rivers and the seas. As the great ocean mirrors
the bright heaven which overspreads it, and reflects back the sunlight
and the sheen of the midnight stars in grandeur and loveliness; so
every drop of water, viewed with the knowledge which science has given
to us, sends back to the mind reflections of yet distant truths which,
rightly followed, will lead us upwards and onwards in the tract of
higher intelligences,--

    “To the abodes where the eternals are.”

In the discoveries connected with electricity, we have results of
a more tangible character than are as yet connected with the other
physical forces; and it does appear that this science has advanced
our knowledge of nature and of the mysteries of creation far more
extensively than any other department of purely experimental inquiry.

The phenomena of electro-chemical action are so strange that we must
return for a moment to the consideration of the decomposition of
water, and the appearance of hydrogen at one pole, and of oxygen at
the other. It appears that some confusion of our ideas has arisen
from the views which have been received of the atomic constitution of
bodies. We have been accustomed to regard water,--to take that body as
an example of all,--as a compound of two gases, hydrogen and oxygen;
an equivalent, or one atom of the first, united to an equivalent or
one atom of the last, forming one atom of water. This atom of water we
regard as infinitely small; consequently a drop of water is made up of
many hundreds of these combined atoms, and a pint of water of not less
than 10,000 drops. Now, if this pint of water is connected with the
wires of a galvanic battery, although their extremities may be some
inches apart, for every atom of oxygen liberated at one pole, an atom
of hydrogen is set free at the other. It has been thought that an atom
has undergone decomposition at one point, its oxygen being torn from
it, and then there has arisen the difficulty of sending the atom of
hydrogen through all the combined atoms of water across to the other
pole. A series of decompositions and recompositions have been supposed
to take place, and the communication of effects from particle to
particle.

An attracting power for one class of bodies has been found in one pole,
which is repellent to another class; and the reverse order has been
detected at the opposite pole of a galvanic arrangement.[144] That
is, the wire which carries the current from an excited zinc plate has
a relation to all bodies, which is directly opposite to that which
is exhibited by the wire conveying the current from, or completing
the circuit with, the copper plate. The one, for instance, collects
and carries acids and the like, the other the metallic bases. At the
extremity of one galvanic wire, placed into a drop of water, oxygen is
always liberated; and at the end of the other, necessary to complete
the circuit with the battery, hydrogen is set free.

It appears necessary, to a clear understanding of what takes place in
this experiment, that we should regard each mass, howsoever large, as
the representative of a single atom. Nor is this difficult, as the
following illustration will show.

Let us take one particle of common salt (_chloride_ of _sodium_)
weighing less than a grain, and put it into a hundred thousand grains
of distilled water. In a few minutes the salt has diffused itself
through the whole of the fluid, and in every drop we can detect
chlorine and soda. We cannot believe that this grain of salt has split
itself up into a hundred thousand parts; we conceive rather that the
phenomenon of solution is one of diffusion. One infinitely elastic body
has interpenetrated with another.

Instead of an experiment with a pint of water, let us take our stand
on Dover heights, and, with a gigantic battery at our command, place
one wire into the ocean on our own shores, and convey the other through
the air across the channel, and let its extremity dip into the sea
off Calais pier--the experiment is a practicable one--we have now an
electrical circuit of which the British channel forms a part, and the
result will be exactly the same as that which we may observe in a
watch-glass with a drop of water.

We cannot suppose that the instantaneous and simultaneous effect
which takes place in the water at Calais and at Dover, is due to
anything like what we have studied under the name of convection, when
considering Heat.

A thousand balls are placed in a line touching each other; the first
ball receives a blow, and the last ball flies off with a force exactly
equal to the power applied to the first; none of the intermediate balls
being moved.

We cannot conceive that the particle _A_ excites the particle _B_ next
it, and so on through the series between the two shores; but regarding
the channel as one large drop, charged with the electric principle as
we know it to be, it is excited by undulation or tremor throughout
its width, and we have an equivalent of oxygen thrown off on one side
of the line, and an exact equivalent of hydrogen at the other, the
electro-chemical influence being exerted only where the current or
motion is transferred from one medium to another.[145] The imperfect
character of this view is freely admitted; no other, consistent with
known facts, presents itself by which the effect can be explained. The
fact stands as a truth; the hypothesis by which it is attempted to
be interpreted is open to doubt, and it is opposed to some favourite
theories.

Before we pass to the consideration of the other sources of
electricity, it is important we should understand that no chemical
or physical change, however slight it may be, can occur without the
development of electrical power. If we dissolve a salt in water, if
we mix two fluids together, if we condense a gas, or convert a fluid
into vapour, electricity is disturbed, and may be made manifest to our
senses.[146]

It has been shown that this power may be excited by friction
(machine electricity) and by chemical action (voltaic electricity,
galvanism); it now remains to speak of the electricity developed by
heat (thermo-electricity), the electricity exhibited under nervous
excitement by the gymnotus and torpedo (animal electricity); magnetism
and its phenomena being reserved for a separate consideration.

If a bar of metal is warmed at one end and kept cool at the other,
an electrical current circulates through the bar, and may be carried
off by connection with any good conductor, and shown to exhibit the
properties of ordinary electricity. The metals best suited for showing
the effects of thermo-electricity appear to be bismuth and antimony. By
binding two bars of these metals together at one end, and connecting
the other ends with a galvanometer, it will be discovered that an
electric current passes off through the instrument by the slightest
variation of temperature. Merely clasping the two metals, where bound
together, with the finger and thumb, is sufficient to exhibit the
phenomenon. By a series of such arrangements,--which form what have
been called thermo-electric multipliers,--we obtain the most delicate
measurers of heat with which philosophers are acquainted, by the aid of
which Melloni has been enabled to pursue his beautiful researches on
radiant caloric.

That this electricity is identical with the other forms has been proved
by employing the current thus excited for the purpose of producing
chemical decomposition, magnetism, and electric light.[147]

The phenomenon of thermo-electricity--the discovery of Seebeck, is
another proof of the very close connection of the physical forces. We
witness their being resolved as it were into each other, electricity
producing heat, and heat again electricity; and it is from these
curious results that the arguments in favour of their intimate
relations and actual identity have been drawn. It will, however, be
found to be the best philosophy to regard these forces as dissimilar,
until we are enabled to prove them to be only modified forms of one
principle or power. At the same time it must not be forgotten that
in natural operations we invariably find the combined action of
several forces producing a single phenomenon. The important fact to be
particularly regarded is, that we have evidence that every substance
which is unequally heated becomes the source of this very remarkable
form of electricity.[148]

There exist a few fishes gifted with the very extraordinary power of
producing electrical phenomena by an effort of muscular or nervous
energy.

The _Gymnotus electricus_, or electrical eel, and the _Raia torpedo_,
a species of ray, are the most remarkable. This power is, it would
appear, given to these curious creatures for purposes of defence, and
also for enabling them to secure their prey. The _Gymnotus_ of the
South America rivers, will, it is said, when in full vigour, send forth
a discharge of electricity sufficiently powerful to knock down a man,
or to stun a horse; while it can destroy fishes, through a considerable
space, by exerting its strange artillery.[149]

Faraday’s description of a _Gymnotus_, paralyzing and seizing its
prey, is too graphic and important to be omitted.

“The _Gymnotus_ can stun and kill fish which are in very various
positions to its own body; but on one day, when I saw it eat, its
action seemed to me to be peculiar. A live fish, about five inches in
length, caught not half a minute before, was dropped into the tub.
The _Gymnotus_ instantly turned round in such a manner as to form a
coil, inclosing the fish, the latter representing a diameter across
it; a shock passed, and there, in an instant, was the fish struck
motionless, as if by lightning, in the midst of the waters, its side
floating to the light. The _Gymnotus_ made a turn or two to look for
its prey, which, having found, he bolted, and then went about searching
for more. A second smaller fish was given him, which being hurt in the
conveyance, showed but little signs of life, and this he swallowed at
once, apparently without shocking it. The coiling of the _Gymnotus_
round its prey had, in this case, every appearance of being intentional
on its part, to increase the force of the shock, and the action is
evidently well suited for that purpose, being in full accordance
with the well-known laws of the discharge of currents in masses of
conducting matter; and though the fish may not always put this artifice
in practice, it is very probable he is aware of its advantages, and may
resort to it in cases of need.”[150]

Animal electricity has been proved to be of the same character as that
derived from other sources. The shock and the spark are like those
of the machine; and the current from the animal, circulating around
soft iron, like galvanic electricity, has the property of rendering it
magnetic.

It is important that we should now review these conditions of
electrical force in connexion with the great physical phenomena of
nature.

It is sufficiently evident, from the results which have been examined,
that all matter, whatever may be its form or condition, is for ever
under the operation of the physical forces, in a state of disturbance.
From the centre to the surface all is in an active condition: a state
of mutation prevails with every created thing; and science clearly
shows that influences are constantly in action which prevent the
possibility of absolute repose.

Under the excitement of the several agencies of the solar beams, motion
is given to all bodies by the circulation of heat, and a full flow of
electricity is sent around the earth to perform its wondrous works.
The solar influences, which regulate, and possibly determine, every
physical force with which we are acquainted, are active in effecting
an actual change of state in matter. The sunbeam of the morning falls
on the solid earth, and its influence is felt to the very centre.
The mountain-top catches the first ray of light, and its base, still
wrapt in mists and darkness, is disturbed by the irradiating power.
The crystalline gems, hidden in the darkness of the solid rock, are
dependent, for that form which makes them valued by the proud and gay,
on the influence of those radiations which they are one day to refract
in beauty. The metals locked in the chasms of the rifted rocks are, for
all their physical peculiarities, as dependent on solar influence as is
the flower which lifts its head to the morning sun, or the bird which
sings “at heaven’s high gate.”

Let us, then, examine how far electricity, as distinguished from the
other powers, acts in producing any of these effects.

We find electricity in the atmosphere, which the electrical kite of Dr.
Franklin proved to be identical with that principle produced by the
friction of glass. In the grandeur and terror of a thunderstorm, many
see nothing but manifestations of Almighty wrath. When the volleys of
the bursting cloud are piercing the disturbed air, and the thunders
of the discharge are pealing their dreadful notes above our heads,
the chemical combinations of the noxious exhalations arising from the
putrefying animal and vegetable masses of this earth are effected,
elements fitted for the purposes of health and vegetation are formed,
and brought to the ground in the heavy rains which usually follow these
storms. Science has taught man this--has shown him that the “partial
evil” arising from the “winged bolt” is a “universal good;” and, more
than this, it has armed him with the means of protecting his life and
property from the influence of lightnings. So that, like Ajax, he can
defy the storm. By metallic rods, carried up a chimney, a tower, or a
mast, we may form a channel through which the whole of the electricity
of the most terrific thunder-cloud may be carried harmlessly into
the earth or the sea; and it is pleasing to observe that at length
prejudice has been overcome, and “conductors” are generally attached
to high buildings, and to most of the ships of our navy.[151] It was
discovered that the devastating hailstorms of the south of France
and Switzerland, so destructive to the vineyards and crops, were
accompanied by evidences of great electrical excitation, and it was
proposed to discharge the electricity from the air by means of pointed
metallic rods. These have been adopted, and, it is said, with real
advantage--each rod protecting an area of one hundred yards. Thus it
is that science ministers to our service; and how much more pleasing
is it to contemplate the lightning, with the philosopher, as an agent
destroying the elements of pestilence, and restoring the healthfulness
of the air we breathe, than with the romancer, to see in it only the
dreaded aspect of a demon of destruction.

The laws which regulate the spread of a pestilence are unknown. The
difficulties of the investigation are great, but they are by no means
insurmountable. A plague passes from the east to the west across
the world--it spreads mourning over the gayest cities, and sorrow
sitteth in the streets. The black death rises in the Orient: it goes
on in unchecked strength, and only finishes its course when it has
made the circuit of the civilized world. The cholera spreads its
ebon wings--mankind trembles--watches its progress, and looks upon
the path which is marked by the myriads of the dead, who have fallen
before the dire fiend. The diseases pass away--the dead are buried,
and all is forgotten. The rush and the riot of life are pursued: and
until man is threatened with another advent, he cares not to trouble
himself. Accompanying the last visitation, there appear certain
peculiar meteorological conditions, which point a line of inquiry. It
may or may not be the path which leads to the truth, but certainly
its indications are worthy of careful examination. It may be asked,
can weak man stop a pestilence; can a mortal’s puny hand retard the
afflictions of the Almighty? The question asked--it must be answered in
reverence, yet without fear. No human power can produce a change in the
physical conditions of the earth, or of the air; and if our diseases
are connected with those changes, as beyond all doubt a number of them
are, they lie above man’s control. But when there are indications that
causes secondary to these are producing some dire effect, and when
we know that these secondary causes may be modified, it is sufficient
evidence to prove that man is permitted to control thus far the
afflictions which are sent to try his powers.

We find a disease winging its way from lane to alley and closed court,
sweeping with destructive violence its way through damp cellars and
crowded attics; it is rife with mischief along the banks of reeking
ditches, and on the borders of filthy streams. Certain it is,
therefore, that some ultimate connexion exists between the conditions
of dirt and this speedy death. Can science tell of these? has it yet
searched out the connecting link? Let the question be answered by a few
facts.

When the cholera first made its appearance, and subsequently, it has
been observed that the electrical intensity of the atmosphere was
unusually low.

The disease has departed, and it is then found that the electricity of
the air has been restored to its ordinary condition.

This appears to show some connexion; but how do these conditions link
this physical force with the ditch-seeking disease?

From all stagnant places, from all the sinks of overcrowded humanity,
from fermenting vegetable and from putrefying animal matter, there
are constantly arising poisonous exhalations to do their work of
destruction.

Where death and decay is a law, this must of necessity constantly
occur; but the poisonous reek may be diffused, or it may be
concentrated, and Nature has provided for this, and ordered the means
for rendering the poison harmless.

By the agency of electricity,--probably, too, by the influence of
light,--the oxygen in the air undergoes a peculiar change, by which
it is rendered far more energetic than it is in its ordinary state.
This is the condition to which the name of _ozone_ has been applied.
Now, this ozone, or this peculiar oxygen, always exists in the air we
breathe; but its quantity is subject to great and rapid variations. It
is found that when electrical intensity is high the quantity of this
principle is great; when the electrical intensity is low, as in the
cholera years, the proportion of ozone is relatively low.

This remarkable chemical agent possesses the power of instantly
combining with organic matter,--of removing with singular rapidity all
noxious odours; and it would appear to be the most active of all known
disinfectants.

May we not infer from the facts stated that the pestilence we dread is
the result of organic poison, which from a deficiency of ozone,--its
natural antidote,--exerts its baneful influences on humanity. This
deficiency is due to alterations in the electrical character of the
air, possibly dependent upon phenomena taking place in the sun itself,
or it may be still more directly influenced by variations in the
character of solar light, which we have not yet detected, by which the
conditions of the electric power are determined.

This may be a line along which it is fair to push enquiry. But such
an enquiry must be made in all the purity of the highest inductive
philosophy, and speculation must be held firmly in the controlling
chains of experiment and observation. In the truths, however, which are
known to us, there is so much harmony and consistence that even the
melancholy theme links itself--a tragedy--with the Poetry of Science.

It has been thought, and much satisfactory evidence has been brought
forward to support the idea, that the earth’s magnetism is due to
currents of electricity circulating around the globe; as a great
natural current from east to west--that, indeed, it has an unvarying
reference to the motion of the earth in relation to the sun.[152]

These terrestrial currents, as they have without doubt a very important
bearing on the structural conditions of the rock-formations and the
distribution of minerals, require an attentive consideration; but we
must, in the first place, examine, as far as we know, the influences
exerted, or supposed to be exerted, by electricity, in its varied forms.

The phenomena of vitality have, by many, been considered as immediately
dependent upon its influence; and a rather extensive series of
experiments has been made in support of this hypothesis. The researches
of Philip on the action of the organs of digestion, when separated
from their connection with the brain, but united with a galvanic
battery, have been proved by Dr. Reid to be delusive;[153] since, as
the organ is not removed from the influence of the living principle,
it is quite evident that the electricity here is only secondary to
some more important power. Matteucci has endeavoured to show that
nervous action is intimately connected with electric excitation, and
that electricity may be made a measurer of nervous irritability.[154]
There can be no doubt that a peculiar susceptibility to excitement
exists in some systems, and this is very strikingly shown in the
disturbances produced by electric action; but in the experiments which
have been brought forward we have only the evidence that a certain
number of muscular contractions are exhibited in one animal by a
current of electricity, giving a measured effect by the voltameter,
which are different from those produced upon another by a current of
the same power. An attempt has recently been made by Mr. A. Smee to
reduce the electrical phenomena connected with vitality to a more
exact system than had hitherto been done. We cannot, however, regard
the attempt as successful. The author has trusted almost entirely
to analogical reasoning, which is in science always dangerous.[155]
In the development of electricity during the operation of the vital
force, we see only the phenomena produced by the action of any two
dissimilar chemical compounds upon each other. It has been thought
that the structure of the brain presents an analogy to that of the
galvanic battery, and the nerves represent the conducting wires.
Although, however, some of the conditions appear similar, there are
many which have no representatives in either the mechanical structure
or the physical properties of the brain, so far as we know it. That
the brain is the centre, the source, and termination of sensation is
very clearly proved by physiological investigations. That the nerves
are the media by which all sensation is conveyed to the brain, and
also the instruments by which the will exerts its power over the
muscles, is equally well established. But to say that we have any
evidence to support the idea that electricity has aught to do directly
with these great physiological phenomena, would be a bold assertion,
betraying a want of due caution on the part of the investigator. That
electric effects are developed during the operations of vitality is
most certain. Such must be the case, from the chemical changes taking
place during respiration and digestion, and the mechanical movements
by which, even during external repose, the necessary functions of the
body are carried on. Whether electricity is the cause of these, or an
effect arising from them, we need not stop to examine, as this is,
in the present state of our knowledge, a mere speculation. We have
no evidence that electricity is an exciting power, but rather that
it is one of those forces which tend to establish the equilibrium of
matter. When disturbed--when its equilibrium is overset--it does, in
its efforts to regain its stability, produce most remarkable effects.
An electrical machine must be rubbed to exhibit any force. In all
galvanic arrangements, even the most simple, dissimilar bodies are
brought together, and the latent electricity of both is disturbed;
and, even in the magnet, it is only when this takes place that its
electrical powers are developed. In the _Gymnotus_, electricity appears
to be dependent upon the power of the will of the animal; but even in
this extraordinary fish, it is only under peculiar conditions that the
electrical excitement takes place, and “what they inflict, they feel”
during the restoration of that equilibrium which is necessary to their
healthy state. In every case, therefore, we see that some power far
superior to this is the ultimate cause; indeed, light and heat, and
probably actinism, appear to stand superior to this principle; and on
these, in some combined mode of action, in all probability, sensible
electricity is dependent. Beyond even these elements, largely as they
are engaged in the organic and inorganic changes of this world, there
are occult powers which may never be understood by finite beings.
We advance step by step from the most solid to the most ethereal of
material creations, and we examine a series of extraordinary effects
produced by powers which we know not whether to regard as material or
immaterial, so subtile are they. On these, it appears, we may exhaust
our inductive investigations--we may discover the laws by which these
principles act upon the grosser elements, and develope phenomena of
a very remarkable kind which have been unobserved or misunderstood.
Whether light, heat, and electricity are modifications of one power,
or different powers very closely united in action, is a problem we may
possibly solve; but to know what they are, appears to be beyond the
hopes of science; and it were idle to dream of elucidating the causes
hidden beyond these forces, and by which they are regulated in all
their actions on dead or living matter.

M. Du Bois Raymond, from a series of researches remarkable alike for
their difficulty and the delicacy with which they have been pursued,
draws the following, amongst many others, as his conclusions as to the
connection of electricity and vital phenomena.

The muscles and nerves, including the brain and the spinal chord, are
endowed during life with an electromotive power, which acts according
to a definite law.

The electromotive power _lasts after death_, or in dissected nerves and
muscles after separation from the body of the animal, as long as the
excitability of the nervous and muscular fibre; whether these fibres
are permitted to die gradually from the cessation of the conditions
necessary to the support of life, or whether they are suddenly deprived
of their vital properties by heat or chemical action.

Let us not suppose for a moment that these conclusions indicate in the
remotest degree that electricity is life,--that vital power is due to
electricity.

During life, with every motion, and, indeed, with every emotion,
whether we move a muscle or exert the mind, there is a change of state.
The result of this is chemical phenomena,--heat and electricity; but
these are not life. We excite them equally by giving motion to a dead
mass.

Notwithstanding the assertions of those who have zealously followed
the path of Mesmer, and examined, or they have thought so, the
psychological effects dependent upon some strange physiological
conditions, there is not an experiment on record,--there is not an
observation worthy of credit, which shows that electricity has any
connection with their results. All around their subject is uncertainty:
doubt involves every experiment, and deception clouds a large number.
Some few grains of truth, and these are sufficiently strange, are mixed
up in an enormous mass of error.

All the phenomena of life,--of the _vis vitæ_ or vitality, are beyond
human search. All the physical forces, or elements, we may examine by
the test of experiment: but the principle on which sensation depends,
the principle even upon which vegetable _life_ depends, cannot be
tested. Life is infinitely superior to every physical force; it holds
them all in control, but is not itself controlled by them; it keeps
its state sacred from human search,--the invisible hidden behind the
veil of mortality.

During changes in the electrical conditions of the earth and
atmosphere, vegetables give indications of being in a peculiar manner
influenced by this power. It is proved by experiments that the leaves
of plants are among the best conductors of electricity, and it has
hence been inferred that it must necessarily be advantageous to
vegetation. That vegetable growth is, equally with animal growth,
subject to electricity, as one of its quickening powers, must be
admitted; but all experiments which have been fairly tried with the
view of stimulating the growth of plants by its agency, have given
results of a negative character.[156] That a galvanic arrangement may
produce chemical changes in the soil, which may be advantageous to the
plant, is probable; but that a plant can be brought to maturity sooner,
or be made to develope itself more completely, under the direct action
of electrical excitation, appears to be one of those dreams of science
which will have a place amongst the marvels of alchemy and the fictions
of astrology. An attentive examination of all the conditions necessary
for the satisfactory development of the plant, will render it evident,
that although the ordinary electrical state of the earth and atmosphere
must influence the processes of germination and vegetable growth,
yet that any additional excitement must be destructive to them. The
wonders wrought by electrical power are marvellous; a magic influence
is exerted by it, and naturally the inquiring mind is led at first to
believe that electricity is the all-powerful principle of creation; but
a little reflection will serve to convince us that it is a subordinate
agent, although a powerful one.

In proceeding with our examination of the phenomena which present
themselves in connection with the terrestrial currents, we purposely
separate magnetism from those more distinct electro-chemical agencies
which play so important a part in the great cosmical operations.

Electricity, we have already stated, flows through or involves all
bodies; but, like heat, it appears to undergo a very remarkable change
in becoming associated with some forms of matter. We have the phenomena
of magnetism when an electric current circulates through a metallic
wire, and it would appear that all other bodies acquire a peculiar
polar condition under the influence of this principle, which will be
explained in the next chapter.

The rocks, taken as masses, will not conduct an electric current when
dry: granite, porphyry, slate, and limestone, obstructing its passage
even through the smallest spaces. But all the metallic formations admit
of its circulating with great freedom. This fact it must, however,
be remembered does not in any way interfere with the hypothesis of
the existence of electricity in all bodies, in what we must regard as
its latent state, from which, under prescribed conditions, it may be
readily liberated. Neither does it affect the question of circulation,
in relation to the great diffusion of electricity which we suppose to
exist through all nature, and to move in obedience to some fixed law.
We know that through the superficial strata electric currents circulate
freely, whether they are composed of clay, sand, or any mixture of
these with decomposed organic matter; indeed, that with any substance
in a moist state they suffer no interruption.

The electricity of mineral veins has attracted much attention, and
numerous investigations into the phenomena which these metalliferous
formations present, have been made from time to time.[157]

By inserting into the mass of a copper _lode_, or vein, in situ, a
metallic wire, which shall be connected with a measurer of galvanic
action, a wire also from the instrument being brought into contact with
another _lode_, an immediate effect is generally produced, showing
that a current is traversing through the wires from one _lode_ to the
other, and completing the circulation probably over the dark face of
the rock in which the fissures forming the mineral veins exist.[158]
The currents thus detected are often sufficiently active to deflect
a magnetic needle powerfully, to produce, slowly, electro-chemical
decomposition, and to render a bar of iron magnetic. These currents
must not be confounded with the great electrical movements around the
earth. They are only to be detected in those mineral formations in
which there is evidence of chemical action going on, and, the greater
the amount of this chemical operation, the more energetic are the
electrical currents.[159] We have, however, very good evidence that
these local currents have, of themselves, many peculiar influences. It
not unfrequently happens that owing to some great disturbance of the
crust of the earth, a mineral vein is dislocated, and one part either
sinks below, or is lifted above its original position; the fissures
formed between the two being usually filled in with clay or with
crystalline masses of more recent formation than the fissure itself. It
is frequently found that these “_cross courses_,” as they are called in
mining language, contain ores of a different character from those which
constitute the mineral vein; for instance, in them nickel, cobalt, and
silver are not unfrequently discovered. When these metals are so found,
they almost invariably occur between the ends of the dislocated lode,
and often take a curvilinear direction, as if they were deposited along
a line of electrical force.[160]

In the laboratory such an arrangement has been imitated, and in a
mass of clay fixed between the galvanic plates, after a short period
a distinct formation of a mineral vein has taken place.[161] By the
action, too, of weak electrical currents, Becquerel, Crosse, and
others, have been successful in imitating nature so far as to produce
crystals of quartz and other minerals. In addition to this evidence, in
support of the electrical theory of the origin of mineral veins, it
can be experimentally shown that a schistose structure may be given to
clays and sandstone by voltaic action.[162]

There is often a very remarkable regularity in the direction of mineral
veins: throughout Cornwall, for instance, they most commonly have a
bearing from the E. of N. to the W. of S. It has hence been inferred
that they observe some relation to the magnetic poles of the earth.
However this may be, it is certain that the ore in any lodes which
are in a direction at right angles, or nearly so, to this main line,
differs in character from that found in these, so called, east and west
lobes.[163]

The sources of chemical action in the earth are numerous. Water
percolating through the soil, and finding its way to great depths
through fissures in the rocks, carries with it oxygen and various
salts in solution. Water again rising from below, whether infiltrated
from the ocean or derived from other sources, is usually of a high
temperature, and it always contains a large quantity of saline
matter.[164] By these causes alone chemical action must be set
up. Chemical change cannot take place without a development of
electricity: and it has been proved that the quantity of electricity
required for the production of any change is equal to that contained
in the substances undergoing such change. Thus a constant activity is
maintained within the caverns of the rock by the agency of the chemical
and electrical elements, and mutations on a scale of great grandeur are
constantly taking place under some directive force.

The mysterious gnome, labouring--ever labouring--in the formation of
metals, and the mischievous Cobalus of the mine, are the poor creations
of superstition. A vague fear is spread amongst great masses of mankind
relative to the condition of the dark recesses of the earth; a certain
unacknowledged awe is experienced by many on entering a cavern, or
descending a mine: not the natural fear arising from the peculiarity of
the situation, but the result of a superstitious dread, the effect of a
depraved education, by which they have been taught to refer everything
a little beyond their immediate comprehension to supernatural causes.
The spirit of demon worship, as well as that of hero worship, has
passed from the early ages down to the present; and under its influence
the genii of the East and the demons of the West have preserved their
traditionary powers.

Fiction has employed itself with the utmost license in giving glowing
pictures of treasures hidden in the earth’s recesses. The caverns
of Chilminar, the cave of Aladdin, the abodes of the spirits of the
Hartz, and the dwellings of the fairies of England, are gem-bespangled
and gold-glistening vaults, to which man has never reached. The
pictures are pleasing; but although they have the elements of poetry
in them, and delight the young mind, they want the sterling character
of scientific truth; and the wonderful researches of the plodding
mineralogist have developed more beauty in the caverns of the dark rock
than ever fancy painted in her happiest moments.

In all probability the action of the sun’s rays upon the earth’s
surface, producing a constantly varying difference of temperature,
and also the temperature which has been observed as existing at great
depths, give rise to thermo-electrical currents, which may play an
important part in the results thus briefly described.

In connection with these great natural operations, explaining them,
and being also, to some extent, explained by them, we have the very
beautiful application of electricity to the deposition of metals,
called the Electrotype.

Applying the views we have adopted to this beautiful discovery,[165]
the whole process by which these metallic deposits are produced will
be yet more clearly understood. By the agency of the electric fluid,
liberated in the galvanic battery, a disturbance of the electricity of
the solution of copper, silver, or gold, is produced, and the metal is
deposited; but, instead of allowing the acid in combination to escape,
it has presented to it some of the same metal as that revived, and,
consequently, it combines with it, and this compound, being dissolved,
maintains the strength of the solution.[166] A system of revival, or
decomposition, is carried on at one pole, and one of abrasion, or more
correctly speaking, of composition and solution, at the other. By
taking advantage of this very extraordinary power of electricity, we
now form vessels for ornament or use, we gild or silver all kinds of
utensils, and give the imperishability of metal to the most delicate
productions of nature--her fruits, her flowers, and her insects;--and
over the finest labours of the loom we may throw coatings of gold or
silver to add to their elegance and durability. Nor need we employ the
somewhat complex arrangement of the battery: we may take the steel
magnet, and, by mechanically disturbing the electricity it contains, we
can produce a current through copper wires, which may be used, and is
extensively employed, for gilding and silvering.[167] The earth itself
may be made the battery, and, by connecting wires with its mineral
deposits, currents of electricity have been secured, and used for the
production of electrotype deposit.[168]

The electrotype is but one of the applications of electricity to the
uses of man. This agent has been employed as the carrier of thought;
and with infinite rapidity, messages of importance, communications
involving life, and intelligences outstripping the speed of coward
crime, have been communicated. There will be no difficulty in
understanding the principle of this, although many of the nice
mechanical arrangements, to ensure precision, are of a somewhat
elaborate character. The entire action depends on the deflection of a
compass-needle by the passage of an electric current along its length.
If at a given point we place a galvanic battery, and at twenty or one
hundred miles distance from it a compass-needle, between a wire brought
from, and another returning to the battery, the needle will remain true
to its polar direction so long as the wires are unexcited; but the
moment connection is made, and the circuit is complete, the electricity
of the whole extent of wire is disturbed, and the needle is thrown at
right angles to the direction of the current. Provided a connection
between two points can be secured, however remote they are from each
other, we thus, almost instantaneously, convey any intelligence. The
effects of an electric current would appear at a distance of 576,000
miles in a second of time; and to that distance, and with that speed,
it is possible, by Professor Wheatstone’s beautiful arrangements, to
convey whispers of love or messages of destruction.

The enchanted horse of the Arabian magician, the magic carpet of the
German sorcerer, were poor contrivances, compared with the copper
wires of the electrician, by which all the difficulties of time and
the barriers of space appear to be overcome. In the Scandinavian
mythology we find certain spiritual powers of evil enabled to pass
with imperceptible speed from one remote point to another, sowing the
seeds of a common ruin amongst mankind. Such is the morbid creation
of a wild yet highly endowed imagination. The spirit of evil diffuses
itself in a remarkable manner, and, indeed, we might almost assign to
it the power of ubiquity; but in reality its advance is progressive,
and time enters as an element into any calculation on its diffusion.
Electricity is instantaneous in action; as a spirit of peace and
good-will it can overtake the spirit of evil, and divert it from its
designs. May we not hope that the electrical telegraph, making, as it
must do, the whole of the civilized world enter into a communion of
thought, and, through thought, of feeling with each other, will bind us
up in one common brotherhood, and that, instead of misunderstanding and
of misinterpreting the desires and the designs of each other, we shall
learn to know that such things as “natural enemies” do not exist? To
hope to break down the great barrier of language is perhaps too much;
but assuredly we may hope that, as we must do when closer and more
intimate relations are secured by the aids of science, the barrier of
prejudice may be razed to the ground, and not one stone left to stand
upon another? Our contentions, our sanguinary wars, consecrated to
history by the baptism of blood, have in every, or in nearly every,
instance sprung from the force of prejudice, or the mistakes of
politicians, whose minds were narrowed to the limits of a convention
formed for perpetuating the reign of ignorance.

And can anything be more in accordance with the spirit of all that we
revere as holy, than the idea that the elements employed by the All
Infinite in the works of physical creation shall be made, even in the
hands of man, the ministering angels to the great moral redemption of
the world? Associate the distant nations of the earth, and they will
find some common ground on which they may unite. Mortality compels a
dependence; and there are charities which spring up alike in the breast
of the savage and the civilized man, which will not be controlled by
the cold usages of pride, but which, like all truths, though in a still
small voice, speak more forcibly to the heart than errors can, and
serve as links in the great chain which must bind mankind in a common
brotherhood. “None are all evil,” and the best have much to learn of
the amenities of life from him who yet lives in a “state of nature,” or
rather from him whose sensualities have prevailed over his intellectual
powers, but who still preserves many of the noblest instincts, to give
them no higher term, which other races, proud of their intelligence,
have thrown aside. Time and space have hitherto prevented the
accomplishment of this; electricity and mechanics promise to subdue
both; and we have every reason to hope those powers are destined to
accelerate the union of the vast human family.

Electrical power has also been employed for the purpose of measuring
time, and by its means a great number of clocks can be kept in a state
of uniform correctness, which no other arrangement can effect. A
battery being united with the chief clock, which is itself connected
by wires with any number of clocks arranged at a distance from each
other, has the current continually and regularly interrupted by the
beating of the pendulum, which interruption is experienced by all the
clocks included in the electric circuit; and, in accordance with this
breaking and making contact, the indicators or hands move over the dial
with a constantly uniform rate. Instead of a battery the earth itself
has supplied the stream of electric fluid, with which the rate of its
revolutions has been registered with the utmost fidelity.[169]

Electricity, which is now employed to register the march of time,
rushes far in advance of the sage who walks with measured tread,
watching the falling sands in the hour-glass.

The earth is spanned and the ocean pierced by the wires of the electric
telegraph. Already, from the banks of the Thames to the shores of the
Adriatic, our electric messenger will do our bidding. The telegraph
is making its way through Italy, and it is dipping its wires in the
Mediterranean, soon to reach the coast of Africa. They will then run
along the African shores to Egypt and Turkey, and still onward until
they unite with the telegraphs of India, of which three thousand miles
are in progress. From Hindostan these wondrous wires will run from
island to island in the Indian Archipelago, and thus connect Australia
and New Zealand with Europe.

In a few years we may expect to have an instantaneous report in London
of the extraordinary “nugget” discovered by some fortunate gold-digger;
and the exile from his native land in the Islands of the South Pacific
Ocean, may learn every hour, if he will, of the doings of his family
and friends in some village home of England.

FOOTNOTES:

[136] _Traité de Physique_: M. Biot, vol. vii. Becquerel: Annales
de Chimie, vol. xlvi.-xlix. Faraday’s _Experimental Researches in
Electricity_, 2 vols., 1830-1844. _A Speculation touching Electric
Conduction and the Nature of Matter_: by Michael Faraday, D.C.L.,
F.R.S.; Philosophical Magazine, vol. xxiv., 1836. _Objections to the
theories severally of Franklin, Dufay, and Ampère, with an attempt to
explain Electrical Phenomena by statical or undulatory polarization_:
by Robert Hare, M.D., Emeritus Professor of Chemistry in the University
of Pennsylvania.

[137] “A good piece of gutta percha will insulate as well as an equal
piece of shell-lac, whether it be in the form of sheet, or rod, or
filament; but being tough and flexible when cold, as well as soft
when hot, it will serve better than shell-lac in many cases where the
brittleness of the latter is an inconvenience. Thus it makes very good
handles for carriers of electricity in experiments on induction; not
being liable to fracture in the form of thin band or string, it makes
an excellent insulating suspender; a piece of it in sheet makes a
most convenient insulating basis for anything placed on it. It forms
excellent insulating plugs for the stems of gold-leaf electrometers,
when they pass through sheltering tubes, and larger plugs form good
insulating feet for electrical arrangements; cylinders of it, half an
inch or more in diameter, have great stiffness, and form excellent
insulating pillars. In these and in other ways its power as an
insulator may be useful.”--_On the use of Gutta Percha in Electrical
Insulation_: by Dr. Faraday; Philosoph. Mag., March, 1848.

The following deductions have been given by Faraday, in his _Researches
in Electricity_, a work of most extraordinary merit, being one of the
most perfect examples of fine inductive philosophy which we possess in
the English language:--

“All bodies conduct electricity in the same manner from metals to lacs
and gases, but in very different degrees.

“Conducting power is in some bodies powerfully increased by heat, and
in others diminished, yet without one perceiving any accompanying
essential electrical difference, either in the bodies, or in the change
occasioned by the electricity conducted.

“A numerous class of bodies insulating electricity of low intensity,
when solid, conduct it very freely when fluid, and are then decomposed
by it.

“But there are many fluid bodies which do not sensibly conduct
electricity of this low intensity; there are some which conduct it and
are not decomposed; nor is fluidity essential to decomposition.

“There are but two bodies (sulphuret of silver and fluoride of lead)
which, insulating a voltaic current when solid, and conducting it when
fluid, are not decomposed in the latter case.

“There is no strict electrical distinction of conduction which can as
yet be drawn between bodies supposed to be elementary, and those known
to be compounds.”

[138] Faraday’s _Speculation on the Nature of Matter_, already referred
to.

[139] _Experimental Researches_: by Dr. Faraday. _Chemical
Decomposition_, p. 151.

[140] Karsten; Poggendorff’s _Annalen_, vol. lvii.

[141] _Traité Expérimental de l’Électricité et du Magnétisme_:
Becquerel, 1834, Priestley’s _Introduction to Electricity_. _On
Electricity in Equilibrium_: Dr. Young’s Lectures.

[142] Faraday’s _Experimental Researches on Electricity_. This
philosopher has shown, by the most conclusive experiments, “that
the electricity which decomposes, and that which is evolved by the
decomposition of, a certain quantity of matter, are alike. What an
enormous quantity of electricity, therefore, is required for the
decomposition of a single grain of water! We have already seen that
it must be in quantity sufficient to sustain a platinum wire 1/104
of an inch in thickness, red hot, in contact with the air, for three
minutes and three quarters. It would appear that 800,000 charges of a
Leyden battery, charged by thirty turns of a very large and powerful
plate machine, in full action--a quantity sufficient, if passed at once
through the head of a rat or cat, to have killed it as by a flash of
lightning--are necessary to supply electricity sufficient to decompose
a single grain of water; or, if I am right, to equal the quantity of
electricity which is naturally associated with the elements of that
grain of water, endowing them with their mutual chemical affinity.”

[143] _Experimental Researches_: Faraday.

[144] The appearance of acid and alkaline matter, in water acted on
by a current of electricity, at the opposite electrified metallic
surfaces, was observed in the first chemical experiments made with
the column of Volta--(see Nicholson’s Journal, vol. iv. p. 183, and
vol. iv. p. 261, for Mr. Cruickshank’s Experiments; and Annales de
Chimie, tom. xxxvii. p. 233, for those of M. Desormes): _On some
Chemical Agencies in Electricity_: by Sir Humphry Davy.--Philosophical
Transactions for 1807. The various theories of electro-chemical
decomposition are carefully stated by Faraday, in his fifth series
of _Experimental Researches on Electricity_, in which he thus states
his own views:--“It appears to me that the effect is produced by an
_internal corpuscular action_ exerted according to the direction of
the electric current, and that it is due to a force either _superadded
to_ or _giving direction to the ordinary chemical affinity_ of the
bodies present. The body under decomposition may be considered as a
mass of acting particles, all those which are included in the course
of the electric current contributing to the final effect; and it is
because the ordinary chemical affinity is relieved, weakened, or partly
neutralized by the influence of the electric current in one direction
parallel to the course of the latter, and strengthened or added to in
the opposite direction, that the combining particles have a tendency to
pass in opposite courses.”

[145] “This capital discovery (chemical decomposition of electricity)
appears to have been made in the first instance by Messrs. Nicholson
and Carlisle, who observed the decomposition of water so produced. It
was speedily followed up by the still more important one of Berzelius
and Hisinger, who ascertained it as a general law, that, in all the
decompositions so effected, the acids and oxygen become transferred and
accumulated around the positive, and hydrogen, metals, and alkalies
around the negative, pole of a voltaic circuit; being transferred in
an invisible, and, as it were, a latent or torpid state, by the action
of the electric current, through considerable spaces, and even through
large quantities of water or other liquids, again to reappear with all
their properties at their appropriate resting-places.”--_Discourse on
the Study of Natural Philosophy_: by Sir John Herschel, Bart., F.R.S.

[146] Numerous beautiful illustrations of this fact will be found in
Becquerel’s _Traité Expérimental de l’Électricité et du Magnétisme_.

[147] See _Le Feu élémentaire_ of l’Abbé Nollet; Leçons de
Physique, tom. vi. p. 252; _Du Pouvoir thermo-électrique_, by M.
Becquerel--Annales de Chimie, vol. xli. p. 353; also a Memoir by
Nobili, Bibliothèque Universelle, vol. xxxvii. p. 15; _Experimental
Contributions towards the theory of Thermo-Electricity_ by Mr. J.
Prideaux--Philosophical Magazine, vol. iii., Third Series; _On the
Thermo-Magnetism of Homogeneous Bodies, with illustrative experiments_,
by Mr. William Sturgeon--Philosophical Magazine, vol. x. p. 1-116,
New Series. Botto made magnets and obtained chemical decomposition.
Antinori produced the spark. Mr. Watkins heated a wire in Harris’s
Thermo-Electrometer.

[148] A very ingenious application of the knowledge of this fact
was suggested by Mr. Solly, by which the heat of a furnace could be
constantly registered at a very considerable distance from it. See
_Description of an Electric Thermometer_: by E. Solly, Jun., Esq.
Philosophical Magazine, vol. xx. p. 391. New Series.

[149] Humboldt; _Personal Narrative_, Chap. xvii.--Annales de Chimie,
vol. xiv. p. 15.

[150] _Experimental Researches on Electricity._ Series xv.
Consult Sir Humphry Davy: _An Account of some Experiments on the
Torpedo_.--Philosophical Transactions, 1829, p. 15. John Davy, M.D.,
F.R.S.: _An Account of some Experiments and Observations on the
Torpedo_, ibid., 1832, p. 259; and the same author’s _Observations on
the Torpedo, with an Account of some Additional Experiments on its
Electricity_; and Matteucci, Bibliothèque Universelle, 1837, vol. xii.
p. 174.

[151] _On Lightning Conductors_, by Sir William Snow Harris;
_Observations on the Action of Lightning Conductors_, by W. Snow
Harris, Esq., F.R.S.--London Electrical Society’s Transactions.
Numerous valuable papers _On Electricity_, by Sir William Harris, will
be found in the Philosophical Transactions.

[152] Adopting, to a certain extent, this view, Faraday, in his
_Electrical Nomenclature_, proposed for the word pole to substitute
_anode_ (ανω, _upwards_, and ὁδος, _a way_), the way which the sun
rises; and _cathode_ (κατα, _downwards_, and ὁδος, _a way_), the way
which the sun sets. The hypothesis belongs essentially to Ampère.
_Objections to the Theories severally of Franklin, Dufay, and Ampère,
with an Effort to Explain Electrical Phenomena by Statical or
Undulatory Polarisation_, by Robert Hare, M.D., Pennsylvania, will well
repay an attentive perusal.

[153] _Inquiry into the Laws of the Vital Functions._--Philosophical
Transactions, 1815, 1822; _Some Observations relating to the Functions
of Digestion_, ibid., 1829: _On the Powers on which the Functions of
Life in the more perfect animals depend, and on the manner in which
they are associated in the production of their more complicated
results_, by A. P. W. Philip, M.D., F.R.S., L. and E.--The following
extract from the last-quoted of Dr. Philip’s Memoirs, will give a
general view of the conclusions of that eminent physiologist:--“With
respect to the nature of the powers of the living animal which we have
been considering, the sensorial and muscular powers, and the powers
peculiar to living blood, we have found belong to the living animal
alone, all their peculiar properties being the properties of life. The
functions of life may be divided into two classes, those which are
affected by the properties of this principle alone, and those, by far
the most numerous class, which result from the co-operation of these
properties with those of the principles which operate in inanimate
nature. The nervous power we have found to be a modification of one
of the latter principles, because it can exist in other textures than
those to which it belongs in the living animal, and we can substitute
for it one of those principles without disturbing the functions of life.

“Late discoveries have been gradually evincing how far more extensive
than was supposed, even a few years ago, is the dominion of
electricity. Magnetism, chemical affinity, and (I believe from the
facts stated in the foregoing paper, it will be impossible to avoid
the conclusion) the nervous influence, the leading power in the vital
functions of the animal frame, properly so called, appear all of them
to be modifications of this apparently universal agent; for I may add
we have already some glimpses of its still more extensive dominion.”

Refer to Dr. Reid’s papers.

[154] _Electro-physiological Researches_: by Signor Carlo Matteucci;
Phil. Trans. 1845, p. 293, and subsequent years.

[155] Electro-Biology: by Alfred Smee, Esq.

[156] _Observations of Electric Currents in Vegetable Structures_: by
Golding Bird, Esq., F.L.S.; Magazine of Natural History, vol. x. p.
240. In this paper Dr. Bird remarks that his experiments lead to the
conclusion that vegetables cannot become so charged with electricity
as to afford a spark; that electrical currents of feeble tension are
always circulating in vegetable tissues; and that electrical currents
are developed during germination from chemical action.

[157] _On Mineral Veins_: by Robert Were Fox, Esq.; Fourth Report
of the Royal Cornwall Polytechnic Society. _On the Electro-magnetic
Properties of Metalliferous Veins in the mines of Cornwall_: by Robert
W. Fox, Esq.; Phil. Trans. 1830, p. 399.

[158] _Experiments and Observations on the Electricity of Mineral
Veins_: by Robert Hunt and John Phillips; Reports of the Royal Cornwall
Polytechnic Society for 1841-42. _On the Electricity of Mineral Veins_:
by Mr. John Arthur Phillips; Ibid., 1843.

[159] In the lead lodes of _Lagylas_ and _Frongoch_, electrical
currents were detected by Mr. Fox, but none in those of _South Mold_
and _Milwr_, in Flintshire: Cornwall Geological Transactions, vol. iv.
In the lead veins of _Coldberry_ and _Skeers_, in Teasdale, Durham, the
currents detected were very feeble: Reports of the Bristol Association,
1838. Von Strombeck could detect no electric currents in the veins
worked in the clay slate near Saint Goar, on the Rhine: Archiv. für
Mineralogie, Geognosie, &c., von Dr. C. J. B Karsten, 1833. Professor
Reich, however, obtained very decided results at _Frisch Glück_,
_Neue Hoffnung_, _Gottlob_, and in other mineral veins in the mining
districts of Saxony: Edinburgh New Philosophical Journal, vol. xxviii.
1839. The irregularities are all to be explained by the presence or
absence of chemical excitation.

[160] This was remarkably the case at _Huel Sparnon_, near Redruth,
where the cobalt was discovered between two portions of a dislocated
lode; and the same was observed by Mr. Percival Johnson in a small mine
worked for nickel, near St. Austell.

[161] _On the process used for obtaining artificial veins in clay_: by
T. B. Jordan; Sixth Annual Report of the Royal Cornwall Polytechnic
Society. See also my memoir, already referred to, in the Memoirs of the
Geological Survey and Museum of Practical Geology, vol. i.

[162] See Becquerel, _Traité Experimental de l’Electricité, &c.
Electrical Experiments on the formation of Artificial Crystals_: by
Andrew Crosse, Esq.; British Association Reports, vol. v., 1836. The
lamination of clay and other substances is described in my memoir
referred to, Note p. 226.

[163] Report on the Geology of Cornwall, Devon, and West Somerset, by
Sir Henry T. De la Beche: _Theoretical observations on the formation
and filling of Mineral Veins and Common Faults_, p. 349.

[164] The following analyses of waters from deep mines were made by me
in 1840, and, with many others, published in the Reports of the Royal
Cornwall Polytechnic Society.

    Consolidated Mines, Gwennap,
               Cornwall.            In 1,000 grains of water.
        Muriate of soda                        1·5
        Sulphate of lime                        ·5
        Sulphate of iron                        ·15
        Sulphate of copper                     1·25
        Silica                                  ·15
        Alumina                                 ·3
                                               ----
            Total                              3·7

    United Mines, Gwennap.
        Muriate of soda                        1·10
        Muriate of lime                         ·15
        Sulphate of soda                        ·50
        Sulphate of lime                       1·5
        Sulphate of iron                        ·75
        Alumina                                 ·5
        Silica                                  ·15
                                               ----
            Total                              4·65

    Great St. George.
        Muriate of soda                        1·35
        Sulphate of lime                        ·74
        Carbonate of iron                       ·70
        Alumina                                 ·50
        Carbonate of lime                       ·10
                                               ----
            Total                              3·4

[165] The discovery of the electrotype has been disputed, as all
valuable discoveries are. Without, however, at all disparaging the
merits of what had been done by Mr. Jordan, I am satisfied, after
the most careful search, that the first person who really employed
electro-chemical action for the precipitation of metals in an
ornamental form, was Mr. Spencer, of Liverpool.

[166] See Spencer, _Instructions for the Multiplication of works of Art
in Metal by Voltaic Electricity. Novelties in Experimental Science_:
Griffin, Glasgow, _Elements of Electro-Metallurgy_: by Alfred Smee, Esq.

[167] The magneto-electrical machine is employed in Birmingham for this
purpose; but I am informed by Messrs. Elkington that they do not find
it economical, or rather that the electro-precipitation is carried on
too slowly.

[168] This has been done by Mr. Robert Were Fox, at a mine near
Falmouth. By connecting two copper wires with two lodes, and bringing
them, at the surface, into a cell containing a solution of sulphate
of copper, this gentleman obtained an electrotype copy of an engraved
copper-plate.

[169] This has been most effectually accomplished by Mr. Bain. Mr.
Hobson has had an electric clock, thus excited, in action for several
years.

CHAPTER X.

MAGNETISM.

  Magnetic Iron--Knowledge of, by the Ancients--Artificial
    Magnets--Electro-Magnets--Electro-Magnetism--Magneto-
    Electricity--Theories of Magnetism--The Magnetic Power of soft Iron
    and Steel--Influence of Heat on Magnetism--Terrestrial
    Magnetism--Declination of the Compass-needle--Variation of the
    Earth’s Magnetism--Magnetic Poles--Hansteen’s Speculations--Monthly
    and Diurnal Variation--Dip and Intensity--Thermo-Magnetism--Aurora
    Borealis--Magnetic Storms--Magnetic conditions of
    Matter--Diamagnetism, &c.

Agreeably with the view now generally received, that magnetism and
electricity are but modifications of one force, since they are found to
stand to each other in the relation of cause and effect, the separation
which is here adopted, of the consideration of their several phenomena,
may appear inappropriate. The importance, however, of all that is
connected with magnetism, and the very decided difference which is
presented by true magnetic action, and that of frictional or chemical
electricity, is so great that it has been thought advantageous to adopt
the present arrangement in reviewing the influence of terrestrial
magnetism with which science has made us acquainted.

From a very early period a peculiar attractive force has been observed
in some specimens of iron ore. Masses of this kind were found in
Magnesia, and from that locality we derive the name given to iron in
its polar condition. This is confirmed by the following lines by
Lucretius:--

    Quod superest agere incipiam, quo fœdere fiat
    Natura lapis hic ut ferrum ducere possit,
    Quem magnêta vocant patrio de nomine Graii
    Magnêtum, quia sit patriis in finibus ortus.

Again we find Pliny employing the term _magnetic_, to express this
singular power. It was known to the ancients that the magnetic power
of iron, and the electric property of amber, were not of the same
character, but they were both alike regarded as miraculous. The Chinese
and Arabians seem to have known Magnetism at a period long before
that at which Europeans became acquainted with either the natural
loadstone or the artificial magnet. Previously to A.D. 121, the magnet
is distinctly mentioned in a Chinese dictionary; and in A.D. 419 it
is stated in another of their books that ships were steered south by
it.[170]

The earliest popularly received account of its use in Europe is, that
Vasco de Gama employed a compass in 1427, when that really adventurous
navigator first explored the Indian seas. It is highly probable,
however, that the knowledge of its important use was derived from some
of the Oriental nations at a much earlier period.

We have some curious descriptions of the _leading stone_ or loadstone,
in the works of an Icelandic historian, who wrote in 1068. The
mariner’s compass is described in a French poem of the date of 1181;
and from Torfæus’s History of Norway, it appears to have been known to
the northern nations certainly in 1266.

We have not to deal with the history of magnetic discovery, but so
far as it tells of the strange properties which magnets are found to
possess, and the application of this knowledge to the elucidation of
effects occurring in nature.

A brown stone, in no respect presenting anything by which it shall be
distinguished from other rude stones around it, is found, upon close
examination, to possess the power of drawing light particles of iron
towards it. If this stone is placed upon a table, and iron filings
are thrown lightly around it, we discover that these filings arrange
themselves in symmetric curves, proceeding from some one point of the
mass to some other; and upon examining into this, we shall find that
the iron which has once clung to the one point will be rejected by the
other. If this stone is freely suspended, we shall learn also that
it always comes to rest in a certain position,--this position being
determined by these points, and some attractive force residing in the
earth itself. These points we call its poles; and it is now established
that this rude stone is but a small representative of our planet. Both
are magnetic: both are so in virtue of the circulation of currents
of electricity, or of lines of magnetic force, as seen in the curves
formed by the iron dust, and the north pole of the one attracts the
south pole of the other, and the contrary. By a confusion of terms we
speak of the north pole of a compass-needle, meaning that point which
is always opposite to the north pole of the earth: the truth being
that the pole of the compass-needle, which is so forcibly drawn to the
north, is a point in a contrary state, or, as we may express it, really
a south pole.

There is a power of a peculiar kind, differing from gravitation, or any
other attracting or aggregating force with which we are acquainted,
which exists permanently in the magnetic iron stones, and also in the
earth. What is this power?

Magnetism may be produced in any bar of steel, either by rubbing it
with a loadstone, or by placing it in a certain position in relation to
the magnetic currents of the earth, and, by a blow or any other means,
disturbing its molecular arrangement. This principle appears to involve
the iron as with an atmosphere, and to interpenetrate it. By one magnet
we may induce magnetism in any number of iron bars without its losing
any of its original force. As we have observed of the electrical forces
already considered, the magnet constantly presents two points in
which there is a difference manifested by the circumstance that they
are always drawn with considerable power towards the north or south
poles of the earth. That this power is of the same character as the
electricity which we have been considering, is now most satisfactorily
proved. By involving a bar of soft iron which, being without any
magnetic power, is incapable of sustaining even an ounce weight, with a
coil of copper wire, through which a galvanic current is passing, the
bar will receive, by induction from the current, an enormous accession
of power, and will, so long as the current flows around it, sustain
many hundred pounds weight, which, the moment the current is checked,
fall away from it in obedience to the law of gravity. Thus the mere
flow of this invisible agent around a mass of metal possessing no
magneto-attractive power, at once imparts this life-like influence to
it, and as long as the current is maintained, the iron is endowed with
this surprising energy.

This discovery, which we owe to the genius of Oersted, and which has,
indeed, given rise to a new science, electro-magnetism, may be regarded
as one of the most important additions made to our knowledge.

Current electricity is magnetic; iron is not necessary to the
production of magnetic phenomena, although by its presence we secure a
greater amount of power. The copper wires which complete the circuit
of a galvanic battery, will attract and hold up large quantities of
iron filings, and the wires of the electric telegraph will do the same,
while any signal is being conveyed along them. Again, all the phenomena
common to galvanic electricity can be produced by merely disturbing the
power permanently secured in the ordinary magnet. It was thought that
magnets would become weakened by this constant disturbance of their
magnetism; but, since its application to the purpose of manufacture,
and magneto-electricity has been employed in electro-plating, it has
been found that continued action for many years, during which enormous
quantities of electricity have been thus given out and employed in
producing chemical decomposition, has not, in the slightest degree,
altered their powers. Thus a small bar of metal is shown to be capable
of pouring out, for any number of years, the principle upon which the
phenomena of magnetism depend.

There are, however, differences, and striking ones, between ordinary
and magnetic electricity. In the magnet we have a power at rest, and in
the electrical machine or galvanic battery, a power in motion. Ordinary
electricity is stopped in its passage by a plate of glass, of resin,
and many other substances; but magnetism passes these with freedom, and
influences magnetic bodies placed on the other side. It would appear,
though we cannot explain how, that magnetism is due to some lateral
influence of the electric currents. A magnetic bar is placed over a
copper wire, and it hangs steadily in the direction of its length;
an electric current is passed along it, and the magnet is at once
driven to place itself across the wire. Upon this experiment, in the
main, Ampère founds his theory of terrestrial magnetism. He supposes
electrical currents to be traversing our globe from east to west, and
thus, that the needle takes its direction, not from the terrestrial
action of any fixed magnetic poles, but from the repulsion of these
currents, as is the case with the wire.

It has been found that wires, freely suspended, along which currents
were passing in opposite directions, revolve about each other, or have
an inclination to place themselves at right angles; thus exhibiting
the same phenomenon as the magnet and the conducting wire. So far the
hypothesis of Ampère leads us most satisfactorily. We see in the magnet
one form of electricity, and in the machine or battery another. But why
should not the electricity of the magnet, electricity at rest, exhibit
the same powers as this force in motion?

Oersted, whose theory led him to the discovery of the fact of the
magnetic power of an electric current, of the establishment indeed of
the new science--ELECTRO-MAGNETISM, regards the phenomena of a current
passing a wire, and its action on a needle, as evidence of two fluids,
positive and negative, traversing in opposite directions, and mutually
attracting and repelling. He conceives that they pass the wires in a
series of spirals; that in the magnet, by some peculiar property of the
iron, this conflict of the currents is reduced to an equilibrium, and
its power becomes manifested in its attractive force.[171] This does
not, however, convey a clear idea to the mind.

It is curious that iron becomes magnetic in a superior degree to any
other metal; that steel retains permanently any magnetism imparted
to it; but that soft iron rapidly loses its magnetic power. This
must be in virtue of some peculiar arrangement of the molecules, or
some unknown physical condition of the atoms of the mass, by which a
continued influence is retained by the steel, probably in a state of
constant internal circulation. It has, however, been shown that soft
iron, under certain circumstances, may be made to retain a large amount
of magnetic force.[172]

If a horse-shoe shaped bar of soft iron is rendered magnetic by the
circulation of an electric current around it, while its two ends are
united by an armature of soft iron, so that it is capable of supporting
many hundred pounds weight; and we then, by breaking the circuit, stop
the current, taking care the armature is kept in contact, the iron will
not lose its magnetic property, but will retain this power for many
years. If the connecting piece of iron, the armature, is removed, the
bar immediately loses all its magnetism, and will not support even the
armature itself. This fact appears to confirm the idea that magnetism
is due to the retention of electricity, and that steel possesses
the property of equalizing the opposing forces, or of binding this
principle to itself like an atmosphere.

The influence of heat on magnetism is so remarkable a proof of the
dependence of this power upon molecular arrangement, that it must not
escape our notice. To select but one of many experiments by Mr. Barlow,
it was found that in a bar of malleable iron, in which, when cold, the
magnetic effect was + 30° 0', all polarity ceased at a white heat, that
it was scarcely appreciable at a red heat, but that at a blood-red heat
it was equal to + 41° 0'.[173]

The more closely we examine the peculiarities of the magnetic power,
and particularly as they are presented to us in its terrestrial action,
the more surprising will its influence appear to be. We have discovered
a natural cause which certainly exercises a very remarkable power
over matter, and we have advanced so far in our investigations as to
have learnt the secret of converting one form of force into another,
or of giving to a principle, produced by one agency, a new character
under new conditions; of changing, in fact, electricity into magnetism,
and from magnetism again evolving many of the effects of electrical