228 GENEVA SOCIETY OF PHYSICS AND NATURAL HISTORY. 



observations it was observed that the pendulums of M. Wolf and M. 



Oppolzer were influenced in their course by the electric register which 



accompanied them, while the pendulum of M. Plantamour, constructed 



by jM. Hipp, was not in the least disturbed. In fact the probable error 



for each combination of longitude is from seven to eight thousandths of a 



second. The measures gave for the difference of longitude between the 



three stations : 



m. s. 



Pfiindler-Zurich 4 53.691 



Gabris-Zurich 3 40.070 



rfiiudler-Gabris 1 13.G21 



M. Eaoul Pictet has proved an anomaly in the law of the diffusion of 

 gases, in the fact that sulphurous acid passes through India rubber with 

 greater facility than hydrogen ; a balloon of india rubber containing 

 sulphurous acid will soon be emptied. By filling with this gas a gl-ass 

 tube closed at the upper end by a sheet of india rubber, and plunging 

 the lower end of the tube into mercury, the rapidity of the escape of the 

 gas may be measured by the ascent of the mercury in the tube. 



Professor Soret has entertained the society at two sessions with some 

 new researches made, with M. Edward Sarasin, upon the rotatory 

 polarization of quartz, particularly for the ultra violet rays, by means 

 of a spectroscope with a fluorescent eyepiece. This instrument was 

 described in the Archives in December, 187G, The results of the labors 

 of MM. Soret and Sarasin are given in the CoDiptcs rcndus de VAcademie 

 des Sciences, t. 83, p. 188. 



Professor Wartmann made a ccminunicatiou uj^on the extrapolar 

 deviations observed upon mercurial conductors, whether vats or 

 troughs. He produced a very sensible current by placing the two 

 extremities of the wire of a galvanometer in the neighborhood of the 

 pole of a current passing through a trough or vat filled with mercury, 

 but beyond the line of the poles. 



Lucien de la Eive presented a work upon the specular reflection of 

 surfaces covered with hairs, considering them as cylinders with a circular 

 base. The author demonstrated that a surface covered with cylinders 

 presented other brilliant points than those of the surface itself. {Ar- 

 chives, 1876, t. 57.) 



Professor Marignac made in his laboratory some experiments upon 

 capsules of tempered glass ; one of them very well resisted the gas 

 flame, but half a minute after the extinction of the flame it exploded 

 like a Rupert's drop. 



M. Theodore Turrettiui observed that a mixture of snow and chloride of 

 magnesium gives a temperature of — 34° C. (—29° P.), while the mixture 

 of snow and chloride of sodium gives only —18° C. (—2° P.) An im- 

 portant use may therefore be made of a product very abundant in mother- 

 waters which has hitherto been thrown away. The double chloride of 



