diaphanous atmosphere by which the head of the comet was surrounded, at a distance of 518,000 kilometers (322,000 English mile 3) from the nucleus. This distance was not constant. The matter of the semi-annular envelope seemed even to be precipitated by slow degrees through the diaphanous atmosphere; finally it reached the nucleus; the earlier appearances vanished; the comet was reduced to a globular nebula. During its period of dissolution, the ring appeared sometimes to have several branches. The luminous shreds of the tail seemed to undergo rapid, frequent, and considerable variations of length. Herschel discerned symptoms of a movement of rotation both in the comet and in its tail. This rotatory motion carried unequal shreds from the center toward the border, and reciprocally. On looking from time to time at the same region of the tail-at the border, for example-sensible changes of length must have been perceptible, which, however, had no real existence. Herschel thought, as I have already said, that the beautiful comet of 1811 and that of 1807 were self-luminous. The second comet of 1811 appeared to him to shine only by borrowed light. It must be acknowledged that these conjectures did not rest on anything demonstrative. In attentively comparing the comet of 1807 with the beautiful comet of 1811, relative to the changes of distance from the sun, and the modifications resulting thence, Herschel put it beyond doubt that these modifications have something individual in them, something relative to a special state of the nebulous matter. On one celestial body the changes of distance produce an enormous effect; on another the modifications are insignificant. OPTICAL LABORS. I shall say very little as to the discoveries that Herschel made in phys ics, since every one is familiar with them. They are to be found in all elementary works, and are given in verbal instruction; they must be considered as the starting-point of a multitude of important labors with which the sciences have been enriched during later years. The chief of these is that of the dark radiating heat which is found mixed with light. In studying the phenomena, not with the eye, as Newton did, but with a thermometer, Herschel discovered that the solar spectrum is prolonged on the red side far beyond the visible limits. The thermometer sometimes rose higher in the dark region than in the midst of brilliant zones. The light of the sun, then, contains, besides the colored rays so well characterized by Newton, invisible rays, still less refrangible than the red, and whose warming power is very considerable. A world of discoveries has arisen from this fundamental fact. The dark ray emanating from terrestrial objects more or less heated also became the subject of Herschel's investigations. His work contained the germs of a large number of beautiful experiments more fully developed in our own day. By successively placing the thermometer in all parts of the solar spectrum, he determined the illuminating powers of the various prismatic rays. The general result of these experiments may be thus enunciated : The illuminating power of the red rays is not very great; that of the orange rays surpasses it, and is in its turn surpassed by the power of the yellow rays. The maximum power of illumination is found between the brighest yellow and the palest green. The yellow and the green possess this power equally. A like assimilation may be laid down beFinally, the power of illumination in the tween the blue and the red. The memoirs of Herschel on Newton's colored rings, though containing a multitude of exact experiments, have not contributed much to advance the theory of those curious phenomena. I have learned, from good authority, that he himself held the same opinion. He said that it was the only occasion on which he had reason to regret having, according to his constant custom, published his labors immediately as fast as they were performed. LIFE AND LABORS OF HENRY GUSTAVUS MAGNUS. [FROM THE ARCHIVES DES SCIENCES PHYSIQUES ET NATURELLES, GENEVA.] Translated for the Smithsonian Report. The processes of scientific investigation have never been reduced to definite rules, and frequently methods are adopted of the most opposite character. Sometimes, impelled by the impulse of his genius to achieve immediate distinction the scientist discards beaten tracks and attempts to explore new regions by assays almost without a definite plan in a predetermined direction, and although the results of his trials in most cases are of a negative character, yet he occasionally lights upon facts rich in the indications of scientific principles. Sometimes, less a lover of novelty than of precision of knowledge, he prefers the critical examination of some region previously traversed by others in order to give it that minute investigation required in every part of the domain of modern science, and thus unostentatiously contributes essentially to the advance of science. These two methods are both fruitful and should not be entirely separated. The first, perhaps the more brilliant, requires an undaunted spirit, a creative genius. The second, more modest, but also more sure, requires extensive erudition, a critical mind, and great talent for experimentation. The scientific career we are about to portray belonged essentially to the latter class. The part of Magnus was less to discover new phenomena than to reinvestigate and render more definite those already known. Such was the precision of his researches that he was frequently enabled to draw new truths from subjects apparently exhausted, and, in some cases, even to transform entirely, propositions generally admitted as truths. He valued little bold conceptions and even ingenious hypotheses when not supported by rigorous demonstration, while a fact apparently the most insignificant he would frequently regard as of the highest importance, provided it was fully established. Exact and conscientious in the extreme, he concentrated his efforts upon the minutiae of his investigations, removing with the greatest care every cause of uncertainty. Of cautious and candid judgment he was not ready to find his scientific colleagues in error; and when a disagreement occurred between his results and those of another, his first impulse was to look for a mistake in his own experiments. Essentially modest, loving science for its own sake, and forgetful of self, he did not shrink from the most arduous labors, from investigations apparently the most unremunerative, and in this way, without ostentation, almost unconsiously he gained a solid and lasting reputation. Henri Gustave Magnus was born in Berlin, May 2, 1802. He belonged to one of the most honorable families of that city. From his earliest infancy he manifested peculiar aptitude for the exact sciences and preferred study to the ordinary amusements of childhood. He passed through all the grades at the academy of Berlin, and received the degree of Doctor in 1827. His first researches were made in the laboratory of Mitscherlich; he next pursued his studies under Berzélius at Stockholm, where he passed the year 1828. Thence he went to Paris where, in the laboratory of Gay Lussac he prepared himself for the interesting experiments which he undertook a few years later. Returning to his native city be soon obtained a reputation as an instructor, which he ever after sustained with great distinction and unflagging zeal. He entered upon this career as private tutor; was nominated in 1834 extra professor, and in 1845 ordinary professor of physics and technology in the university of which he became one of the brightest ornaments. exercised an important influence in developing a taste for the study of physics, as well as in imparting a knowledge of its principles in their most varied applications. For the illustration of the subjects of his lectures he formed the physical cabinet of the university, which was enriched after his death by the valuable collection of apparatus belonging to himself. His first labors were devoted to physical chemistry. In 1825 he contributed to this branch of science, through the Annales de Poggendorff, an interesting memoir, on the property which iron, cobalt, and nickel, finely divided by a reduction of their oxides in a current of hydrogen, possess of taking fire spontaneously in the air at the ordinary temperature. He did not confine himself to the mere discovery of the fact, and to showing that it was an especial attribute of these three metals, but explained it on the principle of De Saussure, of the absorption of gas by porous substances, such as charcoal, and by showing that substances of this character, in consequence of their porosity, condense oxygen and enter into combination with it so energetically as to produce incandescence. In 1828 he discovered the compound which has been called, in compliment to him, the green salt of Magnus. This is formed of the elements of chloride of platinum and of ammonia, and was the first of a series of combinations of the same substances. In an investigation in common with Ammermüller, he discovered the periodic acid, also the ethionic and istheonic acids, analyzed a large number of minerals, and observed the remarkable property which certain crystallized silicates possess, of losing by fusion a considerable portion of their weight. We cannot stop to enumerate all the investigations of Magnus in this branch of science; we must hasten on to his numerous and beautiful researches in physics, which constitute his true claims to renown. These were especially devoted to molecular and calorific phenomena. His first work on physics, entitled "Researches on Capillarity," is rather a study of the flow of different gases, through minute cracks in glass vessels. He throws new light on this subject, and shows the remarkable fact that there is an immense difference in the rapidity of the escape of hydrogen in comparison with other gases. He published later some interesting observations upon evaporation in capillary tubes, which he found most rapid in the narrowest tubes, and upon the boiling of mixed liquids. In regard to the latter, he showed, as theory indicated, that this boiling takes place at the temperature when the sum of the tension of the mixed vapors is just sufficient to overcome the pressure of the atmosphere, consequently at a temperature, a little lower than the boiling-point of the more volatile liquid. He observed that this condition is never realized when the more volatile liquid is placed below the other; the mixture in that case becomes overheated and commences to boil suddenly with a violent explosion. It was also at this period of his life, in the commencement of his career as professor, that Magnus made his interesting experiments upon the gases contained in the blood. This subject has since been further developed, but the honor will always be his, of having materially enlarged the views entertained in regard to one of the most important functions of animal life. The theory of respiration most generally received before his day, was that of Lavoisier, according to which, the combustion of the blood takes place at the moment when it comes in contact with the air in the lungs. This theory was, in fact, the only one then possible, since the presence of gas in the blood, emitted by expiration, had not been shown. Magnus found in arterial as well as venous blood considerable quantities of oxygen, nitrogen, and carbonic acid. The sum of these three gases was, in his experiments, equal to the eighth part of the entire volume of gas. He found that in arterial blood the oxygen was from one-third to one-half; of the carbonic acid in the venous blood only one-fourth to one-fifth. From this he concluded that the oxygen does not combine immediately in the lungs with the carbon of the blood, but absorbed by the arterial blood it is carried into the capillary vessels, where it is employed in the combustion of the debris of the organisms. Carbonic acid is in this way produced, which is also absorbed and transported by the venous blood, and is breathed out at once on reaching the lungs. This theory is now generally adopted. The researches of Magnus, which perhaps more than any other tested his talents for experimentation, are those upon the coefficient of the dilatation of gases. It had been generally admitted that this coefficient was the same for all gases, and that between 0° and 100° C. their volume increased for each degree 0.375 of their volume at 0. This law of Gay Lussac, confirmed by Dulong and Petit, had passed into the domain of undisputed facts, when, four years after the publication of the works of the French savant, a Swede, Rudberg, revived the investigation of this question, and found as value of the coefficient of the dilatation of air 0.3646. It was important that a quantity so continually applied in physical science should be positively determined, |