REPORT ON THE TRANSACTIONS 



OP THE 



SOCIETY OF PHYSICS AND NATURAL HISTORY OF GENEVA, 



FROM JULY, 1865, TO JUNE, 1866. 



BY DOCTOR GOSSE, PKESIDENT. 



TRANSLATED FOR THE SMITHSONIAN INSTITUTION. 



A rule of the society imposes on me the obligation of retracing the principal 

 subjects which have occupied attention during the year just elapsed. In pro- 

 ceeding to acquit myself of this official duty, I should state in advance that the 

 large number of the communications made to the society in its eighteen sessions, 

 while it evinces the scientific interest and constantly increasing zeal which have 

 animated our periodical reunions, leaves me no option but to restrict this notice 

 to the communications in which our members have taken the initiative. The 

 review, however, will at least have the advantage of being conscientiously exact, 

 since it will be based on accurate minutes kept by our worthy secretary, M. Al- 

 exander Prevost. Without changing anything in the plan adopted in the pre- 

 ceding years, I have simply added the date of each communication, with a view 

 of securing to the several authors the priority which belongs to them. 



PHYSICAL SCIENCES. 



Experiinental and theoretical physics. — Professor Wartmann described (Sep- 

 tember 7, 1865) a pneumatic meicurial jmynj), for the consti'uction of the tubes of 

 Geissler, and of bai-ometers and instruments requiring as perfect a vacuum as pos- 

 sible ; reminding us, at the same time, that the first practical apparatus designed 

 for the production of this vacuum was due to Mr. "Welsh, who applied it in the 

 atelier at Kew. In a recent number of his annals, M. Poggendorf has published 

 a modification of Geissler's pump, which requires the use of an ordinary pump 

 and of a great quantity of mercury. No detailed description of the instrument 

 employed by the artist of Bonn having been given, M. Wartmann has constructed 

 one, all the parts of which are stationary, and which requires but a moderate 

 quantity of mercury. A siphon of wrought iron, with vertical branches, com- 

 municating by an inferior tube provided with a cock, serves to fill completely with 

 mercury the receiver which it is proposed to exhaust of air. Thn mercury 

 reaches this receiver by injection from below upwards, and the action of heat 

 sufiices to expel the vapor and air adhering to the walls. The tube, when full, is 

 closed by an upper cock, emptied of mercury by the lower cock, and finally closed 

 (after having received by means of a lateral tube any rarefied gas which it is to 

 contain) by the fusion of its two tubular extremities with tbc blow-pipe. 



A memoir was read by the same member (October 5, IS65) on the maximum 

 explosive distance between the sequent electrodes for the current induced by the 

 opening of the circuit of Ruhmkorff''s apparatus. He has ascertained that the 

 spark is longest when it passes between the positive exterior and the negative in- 

 terior electrodes. There is here, therefore, an influence of the direction of the 



