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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 isstill 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

atmosphere, having for center the magnetic pole. By transmitting through a rarified gas an electrical discharge around the pole of a strong magnet, he caused a luminous ring to appear, animated with a movement of rotation around this same pole. This experiment is so beautiful that it must be admired even by those physicists, now few in number, who consider that the aurora is derived from a source far beyond the terrestrial atmosphere, and attribute to it a cosmical origin. He writes thus to me, only a short time before the attack of illness which caused his death: "Assist me in defending a theory, which I believe to be founded upon incontestable facts, and which was advocated by Franklin and Arago when there was less evidence in its favor. The investigators who study only the brilliant and occasional auroras of our latitudes, should also take into consideration those less radiant that appear almost every day in the polar regions. I do not know a single observer, placed in our extreme northern countries, who does not support the views I have adopted. Surely it is much in their favor that they are advocated by men who live in the midst of the phenomena; and shall we abandon them because they are opposed by those who witness these remarkable appearances only occasionally, and under the influence of surprise and astonishment which must more or less affect the judgment concerning them?"

At the equator, the silent magnetic agitations are replaced by electrical storms, accompanied by thunder and rain, marking, so to say, the course of the sun; and if there is a constant manifestation of auroral phenomena, more or less distinct at each pole, there is always an orange tint, of greater or less intensity, at some point of the equator. What purpose do they serve, these electric manifestations, continually exhib ited throughout the atmosphere of the earth? We are not yet in a condition to say, but De La Rive has thrown much light upon the question. When, a hundred years ago, Priestley discovered oxygen, the agent of combustion and respiration, medicine found a valuable auxiliary, and enthusiasts saw in it a means of prolonging life. The experiments of M. Bert, however, proved that this vital air, if inhaled into the lungs in a pure state, was a mortal poison. This same oxygen, as soon as it is electrized, shows that it is accompanied by a very odorous substance, blackening colored bodies, irritating violently the respiratory organs, and converting animal products into saltpeter. This is the ozone M Schönbein, the celebrated professor of Basle, found at times in the atmosphere, particularly when the latter was electrized by thunderclouds. Auguste De La Rive and his learned friend M. de Marignac maintained that ozone is a modification of oxygen, a conclusion rendered incontestable by our two eminent associates, MM. Frémy and Becquerel, jr.

If pure oxygen is deadly in its effects, mingled with the air that surrounds us, it supports life; and if oxygen, ozenized, is a poison, in mod

erate doses, it purifies the air and fertilizes the soil broken by the plow, giving to its products their agricultural significance.

If it is chance that provides the atmosphere with only just enough of this useful yet dangerous oxygen to support respiration; that brings into being ozone to destroy the deleterious influences which threaten our lives, and to prepare the nourishment necessary for the plants which supply us with food; if it is this same chance which fixes the limits to the concentration of oxygen, rendering almost immutable the quantity of inert gas mingled in the air that we breathe; which renders possible and durable for centuries the existence of man upon the earth, then we must conclude, with Auguste De La Rive, that chance is very intelligent; indeed, so intelligent as to deserve another name.

A flourishing industry, which was commenced about thirty-five years ago, under the auspices of the Academy of Sciences-that is, electroplating-originated in the experiments and practical applications of our respected associate. Up to that time the only mode known of gilding bronze was by the use of mercury. This process produced a good and solid surface, but was fatal to the workmen, as their hands were brought in contact with the dangerous metal, and their lungs exposed to the action of the mercurial vapors during the heating of the articles to be gilded. The old academy offered a prize to any one who would obviate the danger attached to this industry, but it was unclaimed. The present academy was more fortunate. But, if the industry is indebted for its stimulation to the galvanic process, we should not forget that the first pieces gilded by electricity came from the hands of the sagacious and disinterested physicist whose labors we are contemplating. Thanks especially to him, we are spared the distressing spectacle formerly presented by hundreds of unfortunate workmen, involuntary witnesses of the deleterious effects of mercury, who, trembling in every limb, were diseased alike in mind and body.

Auguste De La Rive was a lover and patron of the fine arts, and it was in some sort under his direction that the celebrated painter of Alpine scenery, Calame, executed his chef-d'oeuvre, Mount Rose, the most beautiful ornament of the parlor of the scientist. It represents a rugged, lonely scene, a high plateau in the mountains, without verdure or any trace of the presence of man. In the background is the Alps, in the foreground a small, dark lake and some rocks; that is all. But it is nature in her majesty, flooded with the light and enveloped in the pure transparent atmosphere of the mountains-an unadorned exhibition of her grandeur, affecting powerfully the imagination.

Our philosopher was never tired of the beautiful spectacle presented by the effect of the setting sun upon Mont Blanc, and was led to some interesting scientific observations of the phenomenon through his admiration of its picturesque aspect. At the moment when the sun disappears from the horizon, the valley is covered with shade, and the mountain is gradually obscured from the base to near the summit. This

alone, for some time, remains illuminated, and, suddenly, while the rest of earth sinks into deeper shadow, takes a bright orange tint, sometimes a bloody or fiery red, and appears like an immense meteor, fixed, incandescent, not belonging to earth, but suspended in the sky. Soon the everincreasing shade invades even this icy pinnacle. Its outlines grow indistinct, and its color fades to a cadaverous hue. Like the change from life to death in the human face is this rapid transformation from the brilliant tints of departing day to the livid tone which follows upon the forehead of this giant of rock and snow. No one can witness the solemn spectacle for the first time without profound emotion; and the instinctive silence that falls upon the spectator is like the prelude to a prayer. As he turns sorrowfully away, and asks if all is over, suddenly, as if in answer, the mountain is colored anew with a pale rose tint, the reflection of its former splendor. Is the colossus about to revive? No; this fugitive tint is soon effaced, and darkness covers the scene.

The rosy glow, the day's farewell to the snow-clad peaks of these high mountains, is only the reproduction in a particular form of the general effects of the setting sun upon clouds. But what is the cause of the second coloration? Our associate, after many observations of the summit of Mont Blanc, most frequently subjected to the phenomenon, attributed it to the reflection of the last red rays from vaporous strata accumulated in the up. per regions of the atmosphere. He studied the nature of these vapors, and invented an apparatus for measuring the variations in the transparency of the atmosphere, which are closely observed by the mountaineers, as they judge from them what weather to expect. If the air is perfectly clear, and distant objects plainly visible, the mountains seeming close to the observer, and the sky of a deep-blue color, they will tell you that rain is near, though there may be no other sign of its approach. If the weather is decidedly fine, the air is not perfectly clear, but is pervaded by a bluish vapor, the sky is moderately blue, and mountains seem far away.

Auguste De La Rive supposed that these vapors, characteristic of fine weather, were composed of mineral and organic particles, which float in the air as long as they are dry, but fall to the ground when surcharged with moisture. They are so abundant, that they take from the air its transparency, which is restored when they disappear. The insects which buzz about us are governed by the same law. If the swal lows fly close to the ground at the approach of rain, and high up in the air in fine weather, it is because in the first case the insects upon which they feed are weighed down by moisture, while, in the second, relieved of this burden, they mount higher into space.

The ardor of Auguste De La Rive for the study of electricity could not be satisfied with only the labors of the laboratory. He conceived the plan of a work which would make known all the results obtained in every branch of this department of physics. Familiar with every science, and speaking all languages, he hoped, by uniting and tracing to their source the materials scattered through the periodicals of different coun

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