PHYSICS AND NATURAL HISTORY OF GENEVA. 293 



mour communicated (December 21, I860) certain lesulls arrived at in the ope- 

 rations of this levelling, with the excellent instrument constructed at Aarau 

 by Mr. Kern, and of which the level is particularly accurate. These operations, 

 conducted in concert with the international geodetic commission, are connected 

 with the arc of the meridian, the study of gravitation and that of the form of 

 the terrestrial spheroid. In regions where the slopes are not very great, three 

 or four kilometres are executed in a day, and the error scarcely transcends two 

 or three millimetres to the kilometre. Thus far the levelling has been carried 

 from Neuchatel to Chaumont and the Chasseral ; then by the valley of Ruz, 

 the Chaux-de-Fonds and Locle to Morteau, from Nyon to Saint Cergues and 

 the Rousses, and from Geneva to Morges and Neuchatel. The polygon of 

 levels which connects Neuchatel witli the Chaux-deFonds and Saint Imier has 

 a development of about sixty-one kilometres, and was closed with an error of 

 only fourteen millimetres. In proceeding to connect the stone of Niton with 

 the limnimetre on the quay, it was found that the column must have sunk more 

 than five centimetres in eighteen months. This is owing to the subsidence of 

 the ancient bed of the lake on which the new quay is constructed. The same 

 member communicated to the society (March 15, 1866) the continuation of his 

 researches on the determination of the value of gravitation by means of the 

 pendulum of Re j) sold. He has succeeded in further eliminating some causes of 

 error in considerably prolonging the duration of each experiment. Instead 

 of observing only series of 500 oscillations during six or seven minutes, he has 

 continued his observations for some forty minutes, which have given him nearly 

 3,000 oscillations. These new observations have raised the value of gravitation 

 at Geneva to 9 metres .80381, a result which may be considered as exact to 

 nearly 590000- 



M. Perrot announced (January 4, 1866) that he had succeeded in causing to 

 be constructed a furnace for melting substances such as gold and silver, heated 

 by the ordinary lighting gas. M. Philippe Plaiitamour called the attention of 

 the society (January 10, 1866) to a fact of interest in horology, observed by 

 himself, namely, that in clocks with an anchor escapement, it is the pallet of steel 

 which is worn by the wheel of brass, and that in watches, the pallet of ruby 

 is worn by the teeth of the wheel made of steel. 



Professor de la Rive gave an account (March 1, 1866) of researches made by 

 Professor Dufour of Lausanne, in behalf of the commission of the Helvetic 

 Society charged with the study of terrestrial electric currents After explaining 

 the difficulties met Avith in the observation of these currents, as well as the 

 expedients adopted by M. Dufour to surmount them, M. de la Rive an- 

 nounced that there is an electric current almost constantly passing from Berne 

 to Lausanne, that is to say, from north to souih, though sometimes it exists in 

 the inverse direction. M. Dufour has clearly shown that this is no thermo- 

 electric current. The nearly constant existence of these currents, proceeding 

 from the pole to the equator, connects itself with the continual production of 

 the aurora borealis. When these phenomena augment in intensity and become 

 visible in lower latitudes, the terrestrial currents alsu become more intense. The 

 same member having afterwards (April 5, 1866) resumed an investigation of 

 the phenomena which he had observed in plates of glass submitted to a simple 

 discharge of Ruhmkorff's apparatus, was led to repeat the well known experi- 

 ment of compressed laminae of glass, which exhibit, as long as the compression 

 subsists, certain optical properties. In one of these experiments, the compres- 

 sion having been too sudden, a splinter of glass was detached from the plate, 

 which, although withdrawn from the compression, preserved the optical proper- 

 ties which had been communicated to it. At the same sitting M. de la Rive 

 gave some details on the experiments which he had made in seeking to explain 

 the 'phenomenon of the vibratory movements dete) mined, in the conducting body, 

 by the combined action of magnctis7n atid the discontinuous currents. He has 



