PHYSICS AND NATURAL HISTORY OF GENEVA. 195 



mucli 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 a still gi-eatcr degree perhaps than the barometer, it requires to be observed 

 with scrupulous care, and demands precautions which can scarcely be ex- 

 pected on the part of observers who are not physicists. 



If we pass now to ^j/'y/^/c* 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 

 Itive, 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 clastic fluids. In the classification of his ap- 

 paratus, M. de la liive insists more particularly on the means which he has em- 

 ployed 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 

 platina, in the distilled water placed in the circuit of the principal current. 

 He 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 dimen- 

 sions and form of the gaseous mass, as well as of the j^ressure, on its capacity 

 for transmitting electricity. lie has described the successive appearances 

 which the electric light assumes, in proportion as the pressure of the gas dimin- 

 ishes, 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 centi- 

 metres in length, which sejiarates that photosphere from the stratified luminous 

 column. He has satisfied himself, in the course of a great number of ex- 

 periments, 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. lliess. M. de la Kive has suc- 

 ceeded in showing, by direct experiments, that the mechanical eff"cct in ques- 

 tion 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. lie 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. lie has demonstrated experimentally that if, by means of small sounds 

 of platina suitably arranged, derived currents are taken in different parts of the 

 luminous column, all traversed by the same dischai'ge, great difi'erences will be 

 found in the intensity of these currents, differences which prove that the ob- 

 scure parts possess a greater conducting capacity, and are consequently the most 

 dilated. With 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 ; the 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, in- 

 dicating 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 ex- 

 plaining to the Society the modifications produced in the phenomena relative to 

 the propagation of electricity, through highly rarefied mediums, by the action of 



