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of the dry and pure gas was in the commencement 5mm; at this pressure, as we shall forthwith see, the hydrogen transmits the discharge only under the form of a luminous sheet. The pressure was afterwards augmented solely by means of the vapor of alcohol, with the following results:

Pressure. Number of revolutions in a minute.
Ring, positive. Ring, negative.

7*-------------------- Luminous sheet ------------ 92
10*-------------------- 80 ------------- - - - - - - - - - 52
12*-------------------- 64---------------------- 48
15” -------------------- 48 --------------- - - - - - - - 38
18” -------------- - - - - - - 40 ---------------------- 32
22* -------------------- 30 ---------------------- 25
27mm . . . . . . - - - - - - - - - - - - - - 24---------------------- 18
36mm ........ - - - - - - - - - - - - 12 ---------------------- 10
38” ------------------- - 12 ---------------------- 10

The division into distinct currents, more or less numerous, was manifested when the ring was the positive electrode.

When pure and dry hydrogen is adopted as the medium in which the discharges take effect, the phenomena of rotation are obtained with great difficulty. At rather strong pressures, such as that of 12S*, we have a number of currents, but these currents are too intermittent to allow of the magnet's acting upon them. At 90mm I have obtained a small stream under the form of a bluish-white filament, which, the ring being positive, turned at the rate of thirty-five times per minute; but, at the lapse of some instants, it became subdivided into a multitude of small, irregular streams, and rotation was no longer perceptible. As far as 40”, the action of the magnet was indistinct. At 30mm, the negative ring was covered with small violet sheaths, at equal intervals, which seemed to experience, at the moment it was magnetized, a tendency to move in one direction or the other, according to the direction of the magnetization. The same was the case with the small brilliant points, likewise distributed at minute intervals, with which the ring, when positive, is covered. At 5mm, and still more at three and at two, the ring is entirely covered, when it is negative, with a fine violet-colored sheath, which becomes contracted under the influence of the magnet. The top of the iron rod, which is then positive, is surrounded by a beautiful white aureole, slightly tinged with rose, three centimetres in breadth, and stratified in a very marked degree. Magnetization sensibly contracts this aureole, and compresses its striae without diminishing their number, elevating it, and, at the same time, giving it the form of a pear resting with its base on the magnetic pole. When this pole is the negative electrode, there issues from it, as we have seen, a brilliant tuft of a violet color, which conforms itself to the action of the magnet.

All the phenomena just described show, in a striking manner, the molecular differences which various elastic fluids present, as regards one another, even at an advanced degree of rarefaction. Thus in hydrogen, although that gas is a very good conductor of electricity, electric currents can, with difficulty, and, indeed, scarcely at all, obey the action of the magnet, probably by reason of the slight density of the gas. In air, and in nitrogen, it is quite otherwise, and still more when these gases are humid. The singular property possessed by the electric current of dividing itself into several small and distinct streams, instead of diffusing itself, under the influence of magnetization, when the medium which transmits it contains a more or less quantity of vapor, would seem to indicate in the vapor a greater cohesion than in the gases properly so called, if indeed, we may employ the term cohesion when the question relates to clastic fluids so much rarefied. It might also be possible that this division into streamlets is * 192 PHENOMENA ACCOMPANYING PROPAGATION OF ELECTRICITY.

the result of an optical illusion, due to a very rapid succession of jets emanating from different points, and which, in reality, are not simultaneous. This is a point for examination.

However this may be, it is evident that the study of the stratification of electric light, and of the action of the magnet on the discharges in different gaseous mediums, discloses differences between those mediums which can only result from their difference of molecular constitution. Density, in particular, would appear to have a great influence on this order of phenomena, since we see hydrogen manifest them in so feeble a degree, while the vapors of water, and especially of alcohol and ether, present them in so decided a manner. The proper nature of elastic fluids, opposing more or less resistance to the transmission of electricity, must, doubtless, also play its part. It might not be impossible then, that, in a more detailed and more exhaustive study of the phenomena with which our attention has been occupied, and more particularly of those relating to the action of the magnet on electric currents propagated in much rarefied elastic fluids, we may be able to find the means of acquiring some new ideas on the physical constitution of bodies, and on the manner in which the propagation of electricity is therein effected.




FROM JULY, 1862, TO JUNE, 1863.



In proceeding, as has been the custom of my predecessors, to present an account of the labors of the society during the year just elapsed, it is but proper that I should acknowledge how greatly my task has been facilitated by the scrupulous exactness with which the reports of our several meetings have been drawn up by our secretary, M. Ed. Claparède. Among the topics claiming my attention, many have been already communicated to the public, or are about to be so, through the medium of scientific journals; as regards these, therefore, I shall restrict myself to an indication of the titles, or a very summary analysis of the conclusions arrived at. In the arrangement of subjects I cannot do better than adopt the division into two sections, that of the physical and that of the natural sciences, first proposed by M. de la Rive, and since observed by the greater part of the presidents who have succeeded him. I shall follow, moreover, the example of my immediate predecessor in touching very lightly on the discussions which have taken place either on the occasion of original memoirs read before the society or of verbal reports on recent discoveries made in other countries; not that these discussions have not often possessed a genuine interest, but because it is essential, if this valuable observance is to be retained by us, that the appreciation of the labors of others, the verbal communications in which one is sometimes led to enunciate ideas arising at the moment and perhaps not always sufficiently considered, should receive no greater publicity than that which results from the reading of the journal of our sittings.

PHYSICAL SCIENCES. Our indefatigable colleague, Professor Gautier, has continued to keep the society well informed of the discoveries made in astronomy. His communications have been numerous and diversified; we must here limit ourselves to the mention of the most important. M. Gautier presented to the society, in the first place, a report on the observations of M. d'Arrest, of Copenhagen, relative to the number and to the variability in brightness of the nebula, as well as to certain points, still doubtful, which would tend to indicate a proper movement in some of those bodies ; secondly, an account of a memoir of M. Lamon on the periods of the variations of magnetic declination, and the analysis of researches by M. Maine on the flattening of Mars, which he estimates at zo ; thirdly, a report on some recent observations of M. Donati on the comets, and on a memoir of the same author relative to stellar spectra : M. Gautier announced on this

occasion that Father Secchi also was occupied in the study of stellar spectra compared with the solar spectrum; fourthly, M. Gautier presented lastly to the society a plate of Father Secchi, representing the different appearances of the nucleus of the comet of 1862, differences which, as M. Wartmann, sr., has pointed out, might result, at least in part, from the circumstance that the observations took place at different hours. Professor Plantamour announces that he has collated the series of observations made for twenty years on the latitude of the observatory of Geneva. That latitude would be 46°11'58".75, with a mean error of some hundredths of a second. Meteorology and terrestrial physics establishing a natural bond between astronomy and physics properly so called, we shall first direct our attention to several communications which we owe to Professor Plantamour. Besides the annual meteorological summary for Geneva and Saint-Bernard, published, as usual, in the archives of the physical and natural sciences of the “Bibliotheque Universelle,” M. Plantamour has communicated to the society an interesting memoir relative to observations made at Geneva, for thirty-five years, on the force and direction of the winds. He has found that in winter the number of northeast and that of southwest winds balance each other; the northeast predominates in spring and in autumn, the southwest in summer. The general resultant is a little west of north, which proceeds from the fact that the mean direction of northeast winds more nearly approximates to north than does the mean direction of southwest winds to south. The above results are somewhat modified if the origin of the winds be taken into account and if local are dis. tinguished from general winds. The former depend chiefly on the vicinity of the lake and the variation of temperature in the twenty-four hours, giving rise to a regular breeze morning and evening, analogous to breezes of the land and sea. The memoir of M. Plantamour has been lately published in his extensive work on the climate of Geneva. (See page 15, et sequent.) The same savant read to the society a memoir on the diurnal variations of the atmospheric pressure, a memoir likewise published in the work just mentioned. After having passed in review and combated as insufficient the theories proposed by MM. Krail and Dové, M. Plantamour concludes in favor of that proposed by M. Lamon, according to which the phenomenon of the diurnal variation would depend on two distinct influences, one resulting from the temperature properly so called, the other from a kind of electric attraction, whose nature is as yet completely unknown, but owing probably to the action of the sun. M. Plantamour founds his preference for this theory over the preceding on the consideration that it furnishes the means of explaining the double diurni oscillation which is observed in the barometer, while the influence of the temperature, it would appear, ought to produce but a single one. The author presents, in support of his opinion, a comparative table of the diurnal variation of the temperature and of the barometer for Geneva and Saint-Bernard. To complete our analysis of what relates to terrestrial physics and meteorology, I have still to notice two communications, one from Professor de la Rive, relative to an aurora borealis observed in the month of December, in which the rotation of the arch from east to west was perfectly evident, and another from M. Louis Soret, who has presented to the Society an apparatus constructed according to his directions in the workshop of M. so , an apparatus designed for the measurement of heights by a determination of the temperature of the ebullition of water. In the construction of this instrument, the chief object of M. Soret has been to attain a perfect precision in thermometrical indications, a condition which has heretofore been wanting. He has succeeded, on the one hand, by surrounding the ball of the thermometer with two envelopes of vapor instead of one, in abating the variations of temperature proceeding from without; and, on the other d, he prevents the effect of an ebullition often too much precipitated, by immersing the bottom of the lamp of alcohol, by the flame of which the water is to be made to boil, in a bath of cold water. The sole, yet somewhat grave objection which has been advanced against this apparatus, is, that in astill greater degree perhaps than the barometer, it requires to be observed with scrupulous care, and demands precautions which can scarcely be expected on the part of observers who are not physicists. If we pass now to physics properly so called, we shall see that, as in the past, it is electricity which has played the principal part in the communications made to the Society during the year under review. Our colleague, M. de la Rive, has communicated to us, at two consecutive meetings, the results of his researches on the phenomena which characterize and accompany the propagation of electricity in highly rarefied elastic fluids. In the classification of his apparatus, M. de la Rive insists more particularly on the means which he has employed to measure the intensity of the discharges or transmitted currents, by availing himself of a derived current taken by means of two small sounds of latina, in the distilled water placed in the circuit of the principal current. e also describes a manometer which enables him to appreciate to nearly the fiftieth part of a millimetre, and, for practiced eyes, even to the hundredth part, the tension of the elastic fluid submitted to experiment. The researches of M. de la Rive have been directed to atmospheric air, nitrogen, and hydrogen. - He has studied, in the case of each of these gases, the influence of the dimensions and form of the gaseous mass, as well as of the pressure, on its capacity for transmitting electricity. He has described the successive appearances which the electric light assumes, in proportion as the pressure of the gas diminishes, and particularly the variable form and size of the stratifications of that light, together with the formation of a violet-colored photosphere around the ball serving as a negative electrode, and of a black space, from five to ten centimetres in length, which separates that photosphere from the stratified luminous column. He has satisfied himself, in the course of a great number of experiments, that these appearances of electric light in rarefied gases are due to a mechanical effect produced by the transmission of electricity, an idea which had already been advanced by M. Riess. M. de la Rive has succeeded in showing, by direct experiments, that the mechanical effect in question consists in a considerable dilatation of the gaseous matter near the negative electrode, followed by alternate contractions and dilatations in the column up to the positive electrode. First. He was easily able to verify, by means of the manometer, the existence of the oscillatory movement in the gaseous column, and the variations in its intensity, which depends, as he has shown, on the nature, degree of tension, and dimensions of the gaseous mass in question. Secondly. He has demonstrated experimentally that if, by means of small sounds of platina suitably arranged, . currents are taken in different parts of the luminous column, all traversed by the same discharge, great differences will be found in the intensity of these currents, differences which prove that the obscure parts possess a greater conducting capacity, and are consequently the most dila W. hydrogen, the best conductor of the gases, no derived.current is obtained in the obscure part of the column. Thirdly. M. de la Rive-points out that the indications of the thermometer placed in different parts of the stratified column conduct us to the same results, by evincing great differences between the temperatures of those different parts; o, more obscure parts being sensibly less warm than the luminous, which proves that the former are better conductors. The author has obtained a great number of numerical results, indicating the differences of temperature, at different pressures of various portions of the gaseous column traversed by the discharges. M. de la Rive completed his communication at a subsequent session, by explaining to the Society the modifications produced in the phenomena relative to the propagation of electricity, through highly rarefied * by the action of

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