PHYSICS AND NATURAL, HISTORY OF GENEVA. 201 



operation undertaken by a Swedish expedition for the measurement of an arc of 

 a degree of the meridian at Spitsbergen in the latitude of 78-', and of different 

 inquiries into the spectral lines of the light of planets, stars, and nebulai. He 

 further exhibited to the society specimens of autographic telegraph despatches, 

 some of which were accompanied with draAvings obtained by the system Caselli 

 established between I'aris and Lyons. M. E. Ganticr presented a com- 

 munication on the researches of M. Howlet, relative to the constitution of the 

 sun, and submitted to the society photographs of the sun obtained in different 

 English observatories. These representations show the spots and feculoi with 

 remarkable distinctness. The same associate, after his return from Rome, where 

 Father Secchi had, with much kindness, placed the great refractor of the Roman 

 college at his disposal, gave us an account of the observations which he made 

 on the appearance of the surface of the sun, and of his researches on the physi- 

 cal constitution of that orb. 



. M. Plantamour presented the result of experiments which he had made with 

 a pendulum of inversion, in order to determine, at Geneva, the length of the 

 pendulum which beats seconds. The instrument, executed by M. Repsold, 

 of Hamburg, was confided to him by the federal geodesic commission, and the 

 same apparatus will successively serve to ascertain the gravitation at different 

 points of Switzerland. He also exhibited to the society a portable sun-dial, 

 constructed on a model analogous to those which have been established at a 

 certain number of federal meteorological stations, when the distance from a 

 telegraphic office or the absence of regular postal communications rendered it 

 necessary to furnish observers with the means of obtaining the exact time. 

 These sun-dials have been constructed by j\01. Herrmann and Studer, of Berne. 

 The apparatus exhibited to the society differs from those established penua- 

 nently at the several stations by certain modifications which allow of their being 

 adjusted at any place of which the latitude and the declination of the magnetic 

 needle are known. For this purpose the instrument is provided with a circle, 

 by means of which the axis may be fixed according to the elevation of the 

 equator, and with a compass for adjusting it. The true solar hour may thus be 

 obtained to within a fraction of a minute. 



General Dufour pi'esented a report on the attempts which have been made to 

 construct topographical plots by the help of photography, and showed that com- 

 plete ones can scarcely be obtained in this way, because salient points would 



necessarily mask the others. Professor IMarcet communicated some of 



the results deduced by M. Glaisher from his meteorological discussion of a series 

 of observations made for about ninety years at Greenwich. He called notice 

 particularly to the gradual elevation of mean temperature which seems to have 

 been manifested in the course of that period. 



Professor de la Rive communicated to the society his new researches on elec- 

 tricity, particularly those relating to the influence exerted on the molecular 

 constitution of bodies by the combined action of electricity and magnetism. He 

 has resumed the experiments which he had made in 1846, on the sounds ren- 

 dered by conducting bodies traversed by discontinuous currents, when they are 

 submitted to the influence of a strong electro-magnet, and he is disposed to at- 

 tribute this rupture of molecular equilibrium to an eflect of orientation of the 

 molecules, analogous to that which takes place in magnetic bodies simply tra- 

 versed by a discontinuous current. He has also made experiments on the in- 

 fluence exerted by the vicinity of a very intense magnetic force on the arrange- 

 ment of the metallic particles when these are in process of deposition at the 

 negative electrode in the decomposition of the salts of magnetic metals. Again, 

 the passage of the luminous jet of the Ruhmkorff apparatus across metallic 

 vapors, produced by means of a voltaic arc, has furnished to M.de la Rive very 

 curious and interesting results. This luminous jet assumes, in its passage 

 through these vapors, a well-defined color, varying from one metal to another, 



