(371.) The most obscure part of the subject is no doubt the original mode of disturbance of electrical equilibrium, by which electricity is excited in the first instance, either by friction or by any other of those causes which have been ascertained to produce such an effect: analogies, it is true, are not wanting[56]; but it must be allowed that hitherto nothing decisive has been offered on the subject; and that conjectural modes of action have in this instance too often usurped the place of those to which a careful examination of facts alone can lead us.
(372.) Philosophers had long been familiar with the effects of electricity above referred to, and with those which it produces in its sudden and violent transfer from one body to another, in rending and shattering the parts of the substances through which it passes, and where in great quantity, producing all the effect of intense heat, igniting, fusing, and volatilizing metals, and setting fire to inflammable bodies; even its occasional influence in destroying or altering the polarity of the magnetic needle had been noticed: but as heat was known to be produced by mechanical violence, and as magnetism was also known to be greatly affected by the same cause, these effects were referred rather to that cause than to any thing in the peculiar nature of the electric matter, and regarded rather as an indirect consequence of its mode of action than as connected with its intimate nature. In short, electricity seemed destined to furnish another in addition to many instances of subjects insulated from the rest of philosophy, and capable of being studied only in its own internal relations, when the great discoveries of Galvani and Volta placed a new power at the command of the experimenter, by whose means those effects which had before been crowded within an inappreciable instant could be developed in detail and studied at leisure; and those forces which had previously exhibited themselves only in a state of uncontrollable intensity were tamed down, as it were, and made to distribute their efficacy over an indefinite time, and to regulate their action at the will of the operator. It was then soon ascertained that electricity in the act of its passage along conductors, produces a variety of wonderful effects, which had never been previously suspected; and these of such a nature, as to afford points of contact with several other branches of physical enquiry, and to throw new and unexpected lights on some of the most obscure operations of nature.
(373.) The history of this grand discovery affords a fine illustration of the advantage to be derived in physical enquiry from a close and careful attention to any phenomenon, however apparently trifling, which may at the moment of observation appear inexplicable on received principles. The convulsive motions of a dead frog in the neighbourhood of an electric discharge, which originally drew Galvani’s attention to the subject, had been noticed by others nearly a century before his time, but attracted no further remark than as indicating a peculiar sensibility to electrical excitement depending on that remnant of vitality which is not extinguished in the organic frame of an animal by the deprivation of actual life. Galvani was not so satisfied. He analysed the phenomenon; and in investigating all the circumstances connected with it was led to the observation of a peculiar electrical excitement which took place when a circuit was formed of three distinct parts, a muscle, a nerve, and a metallic conductor, each placed in contact with the other two, and which was manifested by a convulsive motion produced in the muscle. To this phenomenon he gave the name of animal electricity, an unfortunate epithet, since it tended to restrict enquiry into its nature to the class of phenomena in which it first became apparent. But this circumstance, which in a less enquiring age of science might have exercised a fatal influence on the progress of knowledge, proved happily no obstacle to the further developement of its principles, the subject being immediately taken up with a kind of prophetic ardour by Volta, who at once generalized the phenomena, rejecting the physiological considerations introduced by Galvani, as foreign to the enquiry, and regarding the contraction of the muscles as merely a delicate means of detecting the production of electrical excitements too feeble to be rendered sensible by any other means. It was thus that he arrived at the knowledge of a general fact, that of the disturbance of electrical equilibrium by the mere contact of different bodies, and the circulation of a current of electricity in one constant direction, through a circuit composed of three different conductors. To increase the intensity of the very minute and delicate effect thus observed became his next aim, nor did his enquiry terminate till it had placed him in possession of that most wonderful of all human inventions, the pile which bears his name, through the medium of a series of well conducted and logically combined experiments, which has rarely, if ever, been surpassed in the annals of physical research.
(374.) Though the original pile of Volta was feeble compared to those gigantic combinations which were afterwards produced, it sufficed, however, to exhibit electricity under a very different aspect from any thing which had gone before, and to bring into view those peculiar modifications in its action which Dr. Wollaston was the first to render a satisfactory account of, by referring them to an increase of quantity, accompanied with a diminution of intensity in the supply afforded. The discovery had not long been made public, and the instrument in the hands of chemists and electricians, before it was ascertained that the electric current, transmitted by it through conducting liquids, produces in them chemical decompositions. This capital discovery 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 to, and accumulated around, the positive,—and hydrogen, metals, and alkalies round 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 re-appear with all their properties at their appropriate resting-places.
(375.) It was in this state of things that the subject was taken up by Davy, who, seeing that the strongest chemical affinities were thus readily subverted by the decomposing action of the pile, conceived the happy idea of bringing to bear the intense power of the enormous batteries of the Royal Institution on those substances which, though strongly suspected to be compounds, had resisted all attempts to decompose them—the alkalies and earths. They yielded to the force applied, and a total revolution was thus effected in chemistry; not so much by the introduction of the new elements thus brought to light, as by the mode of conceiving the nature of chemical affinity, which from that time has been regarded (as Davy broadly laid it down, in a theory which was readily adopted by the most eminent chemists, and by none more readily than by Berzelius himself,) as entirely due to electric attractions and repulsions, those bodies combining most intimately whose particles are habitually in a state of the most powerful electrical antagonism, and dispossessing each other, according to the amount of their difference in this respect.
(376.) The connection of magnetism and electricity had long been suspected, and innumerable fruitless trials had been made to determine, in the affirmative or negative, the question of such connection. The phenomena of many crystallized minerals which become electric by heat, and develope opposite electric poles at their two extremities, offered an analogy so striking to the polarity of the magnet, that it seemed hardly possible to doubt a closer connection of the two powers. The developement of a similar polarity in the Voltaic pile pointed strongly to the same conclusion; and experiments had even been made with a view to ascertain whether a pile in a state of excitement might not manifest a disposition to place itself in the magnetic meridian; but the essential condition had been omitted, that of allowing the pile to discharge itself freely, a condition which assuredly never would have occurred of itself to any experimenter. Of all the philosophers who had speculated on this subject, none had so pertinaciously adhered to the idea of a necessary connection between the phenomena as Oërsted. Baffled often, he returned to the attack; and his perseverance was at length rewarded by the complete disclosure of the wonderful phenomena of electro-magnetism. There is something in this which reminds us of the obstinate adherence of Columbus to his notion of the necessary existence of the New World; and the whole history of this beautiful discovery may serve to teach us reliance on those general analogies and parallels between great branches of science by which one strongly reminds us of another, though no direct connection appears; as an indication not to be neglected of a community of origin.
(377.) It is highly probable that we are still ignorant of many interesting features in electrical science, which the study of the Voltaic circuit will one day disclose. The violent mechanical effects produced by it on mercury, placed under conducting liquids which have been referred by Professor Erman to a modified form of capillary attraction, but which a careful and extended view of the phenomena have led others[57] to regard in a very different light, as pointing out a primary action of a dynamical rather than a statical character, deserve, in this point of view, a further investigation; and the curious relations of electricity to heat, as exhibited in the phenomena of what has been called thermo-electricity, promise an ample supply of new information.
(378.) Among the remarkable effects of electricity disclosed by the researches of Galvani and Volta, perhaps the most so consisted in its influence on the nervous system of animals. The origin of muscular motion is one of those profound mysteries of nature which we can scarcely venture to hope will ever be fully explained. Physiologists, however, had long entertained a general conception of the conveyance of some subtle fluid or spirit from the brain to the muscles of animals along the nerves; and the discovery of the rapid transmission of electricity along conductors, with the violent effects produced by shocks, transmitted through the body, on the nervous system, would very naturally lead to the idea that this nervous fluid, if it had any real existence, might be no other than the electrical. But until the discoveries of Galvani and Volta, this could only be looked upon as a vague conjecture. The character of a vera causa was wanting to give it any degree of rational plausibility, since no reason could be imagined for the disturbance of the electrical equilibrium in the animal frame, composed as it is entirely of conductors, or rather, it seemed contrary to the then known laws of electrical communication to suppose any such. Yet one strange and surprising phenomenon might be adduced indicative of the possibility of such disturbance, viz. the powerful shock given by the torpedo and other fishes of the same kind, which presented so many analogies with those arising from electricity, that they could hardly be referred to a different source, though besides the shock neither spark nor any other indication of electrical tension could be detected in them.
(379.) The benumbing effect of the torpedo had been ascertained to depend on certain singularly constructed organs composed of membranous columns, filled from end to end with laminæ, separated from each other by a fluid: but of its mode of action no satisfactory account could be given; nor was there any thing in its construction, and still less in the nature of its materials, to give the least ground for supposing it an electrical apparatus. But the pile of Volta supplied at once the analogies both of structure and of effect, so as to leave little doubt of the electrical nature of the apparatus, or of the power, a most wonderful one certainly, of the animal, to determine, by an effort of its will, that concurrence of conditions on which its activity depends. This remained, as it probably ever will remain, mysterious and inexplicable; but the principle once established, that there exists in the animal economy a power of determining the developement of electric excitement, capable of being transmitted along the nerves, and it being ascertained, by numerous and decisive experiments, that the transmission of Voltaic electricity along the nerves of even a dead animal is sufficient to produce the most violent muscular action, it became an easy step to refer the origin of muscular motion in the living frame to a similar cause; and to look to the brain, a wonderfully constituted organ, for which no mode of action possessing the least plausibility had ever been devised, as the source of the required electrical power.[58]
(380.) It is not our intention, however, to enter into any further consideration of physiological subjects. They form, it is true, a most important and deeply interesting province of philosophical enquiry; but the view that we have taken of physical science has rather been directed to the study of inanimate nature, than to that of the mysterious phenomena of organization and life, which constitute the object of physiology. The history of the animal and vegetable productions of the globe, as affording objects and materials for the convenience and use of man, and as dependent on and indicative of the general laws which determine the distribution of heat, moisture, and other natural agents, over its surface, and the revolutions it has undergone, are of course intimately connected with our subject, and will, therefore, naturally afford room for some remarks, but not such as will long detain the reader’s attention.