Chapter IX: Electricity (1)

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]