importance of those investigations and discoveries which had once been despised.

Again, a new conception of the universe, based upon the existence of atoms, the latest representatives of matter, and upon the vibrations of the ethereal medium, the latest symbols of force, induced a certain school to revive doctrines which, originating in Greece, were translated by Lucretius into harmonious verse in order to convert the voluptuous aristocracy of Rome to the philosophy of Epicurus. The Latin poet exclaims in his antique materialism, "He wakes not again who sleeps with the dead; we are only the temporary proprietors of life and not its owners. When the body perishes, the soul also is decomposed; it dissolves as the limbs crumble into dust. The soul dies entirely with the body, and in vain might the earth be mingled with the sea, and the sea with the sky, in one frightful tumult-nothing can ever awaken it."

Modern materialism, content with reviving the doctrines of Epicurus and Lucretius, considers the world as the fortuitous production of the arrangement of atoms; man as the highest development of the natural evolution of organic forms; life as a spontaneous modification of force; birth as the commencement of a phenomenon, death as its end. When, in the light of this philosophy, justice is only a social convention, conscience the fruit of education; charity, friendship, love, only varied forms of selfishness, those intrusted with the care of human souls should acknowledge the terrible power of this contemned science.

The scientific conceptions of the human mind, of great importance as expressions of generalizations, are the result of ideas derived from our present understanding of the phenomena of matter and force, but cannot be considered as absolute truths. Lavoisier, studying chemical actions, the balance in hand, proved, it is true, that in each of these, the weight of the substances produced is equal to that of the substances employed. Let us accept, then, this discovery as a philosophical truth: that matter has weight; that man has never created nor destroyed anything that has weight; in nature, since the universe received its present form, nothing has been lost, nothing created that has weight; matter changes its place, its aspect, and condition, but it does not perish. Is it the same in regard to force? While always remaining imponderable, will it also be variable in its manifestations, perpetual in its activity? Man powerless to create matter, is he equally unable to produce force? Auguste De La Rive has largely assisted in proving that this is the case, and, in so doing, has traced to its highest philosophical consequences one of the most humble experiments of the laboratory, that of Galvani. Two plates, one of zinc the other of copper, produce a sensation when an organ is touched with their two free extremities; the tongue is sensible of a taste; the eye perceives a light; the ear is conscious of sound. By increasing the number of these metallic couples, extending their surface, and plunging them into a saline or acid liquid, Volta constructed his celebrated battery, by which he produced light and heat comparable with those of the

sun, a chemical power superior to that of the volcano, a magnetism equal to that of the earth, and physiological phenomena previously considered as belonging only to manifestations of life. Can it be supposed that all these forces spring from nothing, and that the two metals which produce them remain unchanged in their nature, weight, and other qualities?

German science, still involved in the obscurities of the philosophy of nature, was of this opinion, notwithstanding the experiments of M. Becquerel, sr. Auguste De La Rive thought otherwise; he did not so readily accord to man the faculty of deriving, from nothing, either matter or motion. His mind revolted against such an assumption. He proved, in fact, that no electricity was manifested if one of the two metals was not oxidized; that is to say, if it had not undergone chemical change. The electric current is slight when the chemical action is feeble; intense when it is powerful. The electric circuit starts from the metal attacked and passes over to the other. If both metals are affected at once, the electric circuit begins in the one in which the chemical action is strongest. Change the nature of the medium, and you may reverse at will the action and consequently the direction of the current. The latter experiment is decisive. If the contact of two different metals is sufficient to create the electric current, this ought always to proceed in the same direction. If this current is the result of chemical action, it should, on the contrary, move sometimes in one direction, sometimes in the other, starting from the metal attacked and proceeding toward the one not affected, as was proved by Auguste De La Rive. If we measure the electricity obtained, we ought also to note the chemical force expended. We create nothing; we only transform, Such is the theory of the pile. Faraday devoted much time to the consideration of these truths, but we can do honor to the Genevese physicist while acknowledging our indebtedness to the great English philphilosopher.

If the burning of the coal develops the force of the steam-engine, the zine consumed produces the power of the Voltaic pile. The battery no more creates the electricity that it utilizes than Watt's engine produces the heat that it employs; that electricity comes entirely from the metal burned by the acids. Pursuing this idea, Auguste De La Rive measured the heat which was manifested in the different elements of a battery, in full activity, and found that it did not exceed that produced by the chemical action exerted upon the metal attacked-a conclusion confirmed by the learned dean of the faculty of Marseilles. It is, then, evident that man creates neither electricity, magnetism, heat, nor light; he draws these forces from the reservoirs in which they are hidden and in which they were stored without his aid.

We insist that in nature, as she appears to us, nothing is lost, and nothing is created of that which has weight; we dispose of matter as we choose in order to produce chemical combinations ad infinitum ;

forces are only the causes of movements, which we transform, one into the other at will. Well, is this to say that the world has no other sovereign than man, and that he rules as master? Let us see if this is so. Newton considered light, heat, electricity, and magnetism as so many distinct imponderable fluids. This opinion served as a guide to all the investigations of the eighteenth century and of the commencement of the nineteenth. It was the expression of the truth of the time-was, so to say, the fashion-and it had its fanatical followers, in the first rank of whom was Voltaire. It is now superseded by a theory indicated by Descartes and Huyghens, and which Newton undertook to develop, but abandoned, perhaps because of the difficulties it offered to calculation. This supposes the existence throughout the universe of an elastic, ethereal medium, that is to say, an exceedingly subtile substance, in which float the atoms of ponderable matter. Acting one upon the other, or through internal agitation, these atoms determine, in the ether by which they are surrounded and penetrated, undulations more or less extended, more or less rapid. These vibrations of the ethereal medium constitute light and heat, while electricity and magnetism are the manifestations of the medium itself. Ponderable atoms, an elastic ethereal medium, and the vibrations produced in the latter by the atoms; such is the present conception of the universe. It is simple, true, perhaps, said Auguste De La Rive, but who knows what will be thought of it a hundred years from now? How is it possible to believe that after remaining in ignorance and error in regard to these great subjects from the commencement of the world, man, in less than a century, could acquire complete knowledge of all that concerns them and leave nothing to be discovered by future ages? It behooves us to be more modest, lest our descendants laugh at our audacity.

Among all the different manifestations of the ethereal medium, electricity is the most constant, not only in the reactions of inanimate bodies, but also in the material phenomena we observe in living organisms. It was hastily inferred by some that electricity was life, but Auguste De La Rive would not admit that life could result from this unconscious action of atoms upon ether. He had never seen it manifested spontaneously, and believed that since its first appearance upon earth it had constantly been transmitted from parent to offspring. He considered, moreover, that human personality does not exist in the dust of which our bodies are composed. Is matter that obeys eternal, and the spirit which commands perishable? I would rather, he says, believe that the intelligent soul is immortal and brute matter perishable. He believed the world to have been created and demonstrated as a fact of a scientific order, and, by arguments that M. Clausius afterward developed, that it had not always existed; that it had a beginning, and would have an end.

Ampère, Faraday, and Auguste De La Rive made electricity the subject of profound study, and it was the instrument of their greatest dis

coveries. They were all three very religious, and delighted in meditating upon subjects of a metaphysical character. The first sought to explain universal attraction by magnetism; the second denied even the existence of matter, and considered each atom as a center of force whose vibrations are felt throughout the universe; they endeavored to defend, against the encroachments of the partisans of physical forces the domain of the spirit, that something which thinks, affirms, denies, wills, imagines, feels, and which, free to follow its inclinations, should render an account of its liberty. They were convinced that by such meditations the soul approached the supreme power, whose direct intervention appears like a continued creation.

Belonging to the same school of philosophy, they enjoyed discussing together such questions as the following: Attraction, which sustains. the stars in space, who knows its nature? Affinity, which connects the molecules of bodies, is it not a word whose sense escapes us? We represent matter as composed of atoms; are we sure that these atoms exist? The physiologist describes the phenomena of life; does he know in what life consists? The geologist, who writes the history of the globe of which he has only penetrated the epidermis, does he know its origin and end? If man is proud of the knowledge he has acquired, should he not be humble in view of what he has yet to learn? The publications of our associate are numerous, and attest the activity of his mind as well as the extent and accuracy of his information. But an eminent physicist, M. Soret, is preparing a complete history of them in his native land, and in this article I can only notice a few of their principal features, and, in particular, his beautiful theory of the aurora borealis.

The chronicle of Louis XI reports that, on the 23d of July, 1461, a meteor appeared "of such color and brilliancy that it seemed as if all Paris was in flames;" it adds, in consternation, "May God preserve us!" On the 18th of November, 1465, a similar appearance produced like terror. The king, Louis XI, mounted his horse and rushed to the walls, and the city guard were assembled and posted. The country at that time was in revolt against the government, and it was supposed that the enemy before Paris were attempting to fire the city.

We ourselves witnessed a similar excitement, caused by the appearance of the aurora, during the siege of Paris by the Prussian army. From the beginning of the night until the first actual appearance of the phenomenon, a glow was observed in the north, which gradually deepened into a rose-tint, and spread over half the sky. From time to time colored rays shot forth, of a deep blood-red, while spots of the same sanguinary hue appeared here and there above the city. When the phenomenon had reached its height, and the sky commenced to darken, suddenly the red color shone out again with frightful brilliancy. The next evening the appearance was repeated with somewhat less intensity, but accompanied by luminous white radiations toward a center near the

constellation Pegasus. The inhabitants of Paris were greatly alarmed. They supposed that some great incendiary machine had been put in play, to force the walls or demoralize their defenders. A few of them, seeing that it was a remarkable example of the aurora borealis, sought in it such omens, happy or otherwise, as their excited patriotism suggested.

The Aurora of the North, as Gregory of Tours called it thirteen hundred years ago, varies somewhat in aspect with the latitude. In the polar regions it is so common that it ceases to excite remark, and is often confounded with the twilight. In the center of Europe it is less frequent, and almost always characterized by the deep bloody hue of the sky, and the rays that dart like lances across it. Its appearance justifies the description that it seems as if two great armies, enveloped in fiery vapor, were engaged in mortal combat. In Calabria, where it is still more rare, the imagination finds in it arcades and porticoes, while Greece, always poetical, and very seldom honored by this celestial visitation, sees in the illuminated sky the assembly of the gods in council upon Olympus in the presence of Jupiter.

How are we to account for these appearances? Auguste De La Rive considered that they were produced by electrical conflicts, silent and mysterious, converging toward the magnetic pole of the earth. Every one is familiar with the electric light, whose power is exhibited in the light-house, on the stage, and in public illuminations. This brilliant phenomenon, discovered by Davy, was especially noticed by Arago, who declared, a priori, that it would offer the then strange spectacle of a flame obeying the action of a magnetic bar. Experiment confirmed his prediction. When this luminous arch is approached by the poles of a strong magnet, it is attracted or repulsed; its curvature increases, the brilliancy of the flame diminishes; it is varied by jerks and by flashes of colored light when silk is rubbed near it, and the arch at last breaks, when the curvature is so great that it extends too much the surface passed over by the electrical discharge. A magnetic needle placed in the vicinity manifests, by its incessant agitation, that it is affected by a strong magnetic, influence. Is not this the image of the aurora polaris? Arago devoted many years to the study of the influence of the aurora borealis upon the magnetic needle; and often announced the appearance of the phenomenon in the north of Europe, even before it was manifested in France. He was too cautious, however, to hazard an opinion in regard to its nature. Auguste De La Rive took up the subject-we should rather say, devoted himself to it-and among the many reasons for regretting the death of this illustrious savant is the loss to science of a work he was preparing upon the polar lights, the materials for which he had spared no pains in collecting. The apparatus is well known, at least in the lecture-room, by means of which he reproduced the fundamental conditions of the phenomenon, which he considered due to the formation of a luminous ring in the upper regions of the