REPORT ON THE TRANSACTIONS OF THE SOCIETY OF PHYSICS AND NATURAL HISTORY OF GENEVA, FROM JUNE, 1867, TO JUNE, 1868.

BY PROFESSOR ÉLIE WARTMANN, PRESIDENT.

[Translated for the Smithsonian Institution.]

The report which I have the honor of submitting to my colleagues of the Society is the eleventh of those which have been presented under our existing regulation. Like my predecessors, I propose to recall the different communications which have been made, by grouping them according to their subjects. Like them, too, I would renew the recollection of the amicable discussions, the free and unconstrained developments elicited by the reading of a memoir, or even the simple statement of a question. It is the privilege of our association to have no official connections, to observe only our own traditional customs, and to permit its members to exchange ideas with a mutual kindliness, which certainly does not exclude a sincere love of truth. This form has so many charms and advantages that I trust it will long be preserved. When in 1890 the society shall celebrate the centennial anniversary of its foundation, it will be able to point with pride to the fact that it has served in no stinted measure to unite and encourage those of our compatriots who devote themselves to the culture of the natural sciences.

Thanks to the care taken by our secretary, M. Alex. Prevost, in recording our proceedings, I may hope that my account of them will, at least, have the merit of exactness. The society has held during its current year twelve general and eight special sessions. No modification has been introduced in its rules. The old custom of assembling for tea previous to our winter sessions has, after discussion, been retained.

Dr. Lombard has been called to exercise the functions of president during our approaching term, 1868-'69. M. Marc Micheli has been elected a member in ordinary, as has also M. Godefroy Lunel, who already belonged to us as a free associate. It is with sincere pleasure that I record this increase in the number of our members, which now amounts to 42. No death has occurred among them within the year. Unfortunately, it is not so with our honorary members, three of whom have been taken from us.

Dr. Michael Faraday, one of the most distinguished savants of England, and our associate for a quarter of a century, departed this life 25th August last. The labors of this eminent physicist are too well known to require enumeration here. No time was lost by M. de la Rive in rendering a touching and worthy homage to the successor of Humphry Davy.* I had myself, for several years, cultivated the most pleasant relations with this kind-hearted man, in whom a genius full of originality was allied with the most unaffected modesty. To science, as to his personal friends, the loss is irreparable.

Six months later, Leon Foucault, an intellect of a high order, was withdrawn from us, at the age of 49 years, a victim to immoderate application. He was

* Archives des sciences, physiques, et naturelles, t. xxx, p. 131. This notice has been reproduced in the journal L'Institut, and in the Philosophical Magazine. [also in the Smithsonian Report for 1867, p. 227.]

endowed with no common faculties, and resembled Faraday in the incompleteness of his earlier studies, which both had afterwards found the means of retrieving through special methods, in conjunction with great decision of purpose. Looking upon evidence as the only unimpeachable demonstration of truth, Foucault had conceived and executed the most delicate researches. His mechanical dexterity was incomparable, and, had he lived longer, would have been made available for the solution of many other problems. He was a warm friend, an ingenious and penetrating spirit, a clear and accurate writer. He leaves in the history of physics profound traces which will preserve his name from oblivion. He was received into our society in 1859.

Dr. Charles Daubeney, recently deceased in England at the age of 73 years, has been a colleague of ours since 1830. He had pursued at Geneva, under Pyrame de Candolle, his studies in botany, a science of which he was subsequently a professor in the University of Oxford. We are indebted to him for a great number of researches in different departments of the natural sciences. In our city he had made many friends, to whom he has always remained greatly attached.

After this tribute paid to the memory of savants who are no more, we may. congratulate ourselves on having inscribed upon our list the name of M. Claude Bernard, the distinguished French physiologist. None among us but remembers the interesting communication on the curare, and on poisons in general, which he presented, in 1865, to the Helvetic Society of Natural Sciences, assembled within our walls.

§ 1.-ASTRONOMY.

Has the moon, our nearest neighbor in the immensity of the heavens, arrived at a definitive state, or can we still discover some changes on its surface? This question, so important for cosmology, has been almost universally answered in the negative. Professor Gautier recounted to us (4th July) the researches made at Athens, by Dr. Schmidt, on the transformations undergone by the crater Linnæus, in the Mare Serenitatis. Affirmed by different observers, for instance by M. Respighi, at Bologna, these modifications have been called in doubt by other savants. Thus M. William Huggins maintains that the appearance of the Linnæus is exactly that which Schröter has figured in plate IX of his Selenotopographische Fragmente. This divergency of views gives interest to the observations reported to us by M. Thury, (1st August,) and which he made by means of an excellent refractor, mounted at the atelier of Plainpalais, with an objective, furnished by Mertz, of four and a half inches opening. Our colleague thinks that the crater has become filled with a substance of a whiteness like that of ceruse, so that its configuration differs from that represented by Mädler in his celebrated chart. (See Archives des Sciences, Physiques, et Naturelles, t. XXX, p. 292.)

M. Gautier has continued, as in former years, to communicate to us the uninterrupted progress of the noble science to which he has devoted himself. He announced the arrival at Labrador of two thermometers, which he had sent to the Moravian missionaries through the medium of our countryman, M. J. L. Micheli. These instruments will be used for a regular study of the temperature of those glacial regions. He gave us an account of the researches of Dr. W. Schur on the orbit of the double star p, in Ophiuchus, from which we are authorized to estimate at about 94 years the period of the revolution of the smaller star around the larger. By adopting the value of the annual parallax of this group obtained at Bonn, by Dr. Krüger, the mutual distance of the two stars would appear to be about 30 times the distance from the earth to the sun, the mass of the group to be triple that of the sun, and its light to occupy 20 years in reaching us. He brought to our notice the observations of Dr. Auwers,

at Gotha, on the parallax of the star of eighth to ninth magnitude, No. 34 of the catalogue of Groombridge, the distance of which from the earth is computed to be but 672,000 radii of our orbit. M. Gautier also directed our attention to the improvements effected in different instruments of astronomy and meteorology, and adverted to several new asteroids situated between Mars and Jupiter. The discovery of these planet's commenced with the present century, and their number reaches to-day nearly 100.

Professor Plantamour gave an account (21st November) of the mechanical processes by help of which he takes observations, registered by a chronograph. The scene of his labors this year was the Righi. These observations have reference to the determination of gravitation, and to other questions submitted to study by the International Conference for the measurement of the meridian between two parallels comprising an arc of 22° in middle Europe.

Since the admirable discoveries of Kirchoff and Bunsen relative to the spectral analysis, the learned have investigated with much ardor the problems bearing upon the physical constitution of the sun. One of our colleagues, Colonel E. Gautier, has directed his attention specially to the theory of the spots, and exhibited to us (4th July) an eye-glass manufactured at Munich, which is intended to enfeeble, by polarization, the too vivid lustre of the luminary. It would seem to result from observations conducted with this instrument that the solar spots have a very different appearance from that attributed to them. The importance of enabling astronomers to examine these phenomena gave occasion, almost at the same time, to the invention, by the ingenious Leon Foucault, of a silverplated reflecting telescope. We may hope, therefore, that with the aid of these new instrumentalities science will soon arrive at certain conclusions on this difficult subject. M. E. Gautier has further given, in our meeting of this day, (4th June,) the analysis of a memoir published by M. Sporer, professor at Anclam, on the spots of the sun, in which the author treats of the law of their velocities of rotation according to their heliographic latitudes, and of the irregularities which disturb that law. In effect, neighboring spots seem sometimes to undergo a sort of torsion, with other anomalous appearances. These anomalies result from the modifications, often very rapid, which are observed in the aspect of the spots, when a magnifying power sufficiently strong is employed, and atmospheric circumstances are favorable. We may then recognize variations, resolutions, and new formations comparable to those of our terrestrial clouds. M. Spærer draws from this a confirmation of the idea, already announced by him, that the spots are situated above the brilliant surfaces on which the faculæ are developed. Notwithstanding the accidental changes of velocity whose phases have been studied, the author refuses to believe that the general movement of the solar surface around its axis varies by zones, or by rings parallel to the equator. M. Spærer examines, moreover, the proportional distribution of the spots and faculæ on the different portions of the orb, as well as the relations of this distribution to the phases of the period of 11 years which has been recognized in the frequency of these phenomena. He afterwards attacks the Wilsonian theory regarding the funnel-shaped spots. He exerts himself to weaken the bearing of the calculations of English astronomers on the mean-proportionals which they have deduced from photographic observations of the sun in relation to that theory. He refutes the attempts of M. Faye tending to introduce a correction termed parallax of depth, in order to make the calculation of the places of the spots quadrate with the observations derived from the work of M. Carrington. He maintains the views of M. Kirchoff on the constitution of the sun, and concludes with some ideas touching the manner in which the spots may be formed. They might be generated by intense ascending currents of gaseous matter which burst forth from the sphere in fusion and become condensed in the solar atmosphere at different heights. These formations would remain or fall back according to the

velocity communicated to them by the strata into which they penetrate, and wherein they diffuse themselves.

§ 2.-METEOROLOGY.

Professor A. Gautier read (4th July) an extended notice of the results obtained from December, 1865, to November, 1866, during the third year of observations made at the 76 stations of Switzerland, under the two-fold view of temperatures and quantities of rain. This production has been inserted in volume xxix of the Archives des Sciences, Physiques, et Naturelles. I will content myself, therefore, with citing a conclusion but little known; namely, that the mean temperature of Geneva is higher than that of the other cities of our country, with the exception of Bellinzona, Lugano, Mendrisio, Montreux, and Sion. At the close of the last-mentioned communication, Professor A. de Candolle expressed a regret that the methods by means of which meteorologists establish the mean of the numbers they collect, render the results of their calculations nearly useless to botanists. He remarked that the phenomena of vegetation continue for some months, during which it would be important to know the sums of the temperatures above a certain degree previously fixed upon.

§3.-MATHEMATICS AND PHYSICS.

The sun, that source of complex radiations which call forth the most diverse and important phenomena, dispenses to us heat varying as to quantity with the seasons, and as to composition with the state of the atmosphere. By means of the actinometer which he presented last year to the society, M. L. Soret compared (5th September) the intensity of the calorific radiation at Geneva with its value on the glacier of the Bossons and at the summit of Mont Blanc; he found that when the sun is 60° above the horizon, the radiation at a height of 4810 meters is to that on the plain in the ratio of six to five. The diminution of intensity with the height of the sun is much less considerable at a great altitude than in regions less elevated. To these observations, made in August, M. Soret has added others during the winter, whence it results that, for the same height of the sun, the intensity of the direct radiation is then greater than in summer, which accords with the part which, according to M. Tyndall, is borne, by the atmospheric vapor in the phenomena of absorption. Our colleague has ascertained that, at an equal elevation of the sun, the radiation diminishes more rapidly when the heat has traversed a watery stratum than when the rays are direct. The recital of these results was the occasion of interesting discussions, calculated to guide the author in new experiments.

The question whether the sca is free at the pole was raised in connection with these estimates of the thermic intensity of the solar radiation. M. Soret also took occasion to state (19th December) that ozone, prepared by the action of the apparatus of Ruhmkorff on oxygen, possesses the same density with that obtained by electrolyzing water. (Archives des Sciences, &'c., t. xxx, p. 306)

Professor de la Rive presented (6th February) the analysis of researches by M. Elias Loomis, leading to conclusions very favorable to the electric theory of polar auroras, proposed by our colleague. (Archives des Sciences, &c., t. xxxi, p. 273.)

Among the phenomena whose study promises to enlarge the field of our knowledge of the intimate constitution of bodies, none are more interesting than those of rotary polarization. Detected in quartz by Arago, in 1811, this mysterious property has been found in solids of regular system, in homogeneous colorless liquids, and in certain vapors, though no permanent gas, even when compressed, has heretofore manifested it. It is therefore independent of the crystalline state, and, according to the substance employed, takes place some

times to the right, sometimes to the left of the observer. Further, it may vary in direction in the same body with the tint of the light which traverses it, for we have notice of a liquid which is lævogyral for the rays of one extremity of the spectrum and dextrogyral for those of the other extremity. When Faraday found, in 1845, that the plane of polarization of a ray traversing an inactive. substance may be made to turn by placing the substance within the magnetic field, he enhanced in an unexpected manner both the interest and the difficulty of this problem of molecular mechanics. Wiedemann showed that this artificial rotation increases in proportion as the length of wave of the colored ray diminishes. Verdet ascertained that there exist substances for which the rotation is positive, others for which it is negative, (that of water being taken for unity,) but that it is not necessarily connected with refrangibility. Wertheim deduced from his experiments that in general it is absent in solids endued with double refraction.

Is rotary polarization owing to an action exerted by the substance which transmits the luminous (or calorific) ray, or should it be referred to an influence experienced by the ether which surrounds and penetrates matter, properly so called? The first of these suppositions was taken into favor when Faraday found that the magnetic rotation is distinguished from the natural, by the very important fact that it augments with the length of the course of the ray, whether direct or reflected, in the transparent medium.

Professor de la Rive has resumed the study of this subject, and communicated to us (7th May) a comprehensive review of his experiments. These have been made with divers solids, among others glass compressed by the fulminating discharge of Ruhmkorff's machine, as well as with different liquids. Our distinguished colleague had already remarked, (Traité d'Electricité, t. i, p. 555,) that the phenomenon seems connected in an essential manner with the density more or less considerable of the intermolecular ether, and consequently with the refractive power of bodies; but in his new researches he has found that the density of the body itself exercises a great influence, independently of that of the ether which it includes. Thus, with the electro-magnetic intensity at his disposal, he has ascertained that the rotation being 8° in sulphur of carbon having a density of 1,263, it became 16°, that is precisely double in thallic alcohol, a liquid of which the refrangibility is slightly superior, and which possesses a density much more considerable, (3.55.)

It is known that the rotation of the plane of polarization persists for some instants after the electric current has been interrupted. M. de la Rive has satisfied himself by a great number of experiments in which he has succeeded in measuring the duration of that persistence, and in appreciating the circumstances which influence it, that this effect cannot be explained by the inertia of the ponderable molecules. It is a consequence of the magnetism remaining in the iron of the electro-magnet, for it no longer takes place when inductive spirals simply, without a metallic nucleus, are employed. M. de la Rive concludes that artificial rotary polarization, although greatly influenced by the molecular constitution of bodies, is not due to an alteration which magnetism might determine in that constitution, but rather to an action exerted indirectly on the ether through the medium of the ponderable particles. This explains why the phenomenon depends at once on the state of the intermolecular ether, and on the arrangement of the number and the nature of the particles in a given volume of a body.

M. Achard recapitulated (April 16) the conclusions of a popular lecture given by M. Clausius on the second principle of the mechanical theory of heat. According to the last-named savant, the work which natural forces can execute, and which is contained in the movements of the different bodies of the universe, is successively tranformed into heat. This heat seeks incessantly to pass from warmer bodies into colder ones, so that there will be gradually established a definitive equilibrium between the heat radiating into ether and that which