DE LA RIVES RESEARCHES. 157 



and here we have seen a way of getting it without any pump at 

 all. 



I now beg to call upon M. Sarasin-Diodati to give his communi- 

 cation on " M. de la Rive's Experiments in Statical Electricity." 



M. SARASIN-DIOD ATI'S ADDRESS UPON AUGUSTE DE LA RIVE'S 

 LAST RESEARCHES IN ELECTRICITY. 



M. SARASIN gave an account of the last works of Auguste de la 

 Rive, conjointly with whom he had often worked, and he described 

 some of his instruments, which were sent to the exhibition, from 

 Geneva. 



He stated that M. dc la Rive and he himself had repeated in order 

 to study them more accurately the observations previously made by 

 Pliicker, by De la Rive himself and by others, upon the modifications 

 which the electric discharge undergoes, in rarefied gases, under the action 

 of magnetism. They first of all considered the case in which the spark 

 is produced perpendicularly to the line of the poles of the magnet, work- 

 ing for that at pressures included between i moil and io mou . In this case 

 the discharge is deviated and tends to describe a circular curve around 

 the axis of the magnet ; moreover the luminous jet is more condensed 

 and has all the characteristics which it shows at a higher pressure. 

 MM. de la Rive and Sarasin have verified the fact that the resistance 

 offered to the passage of the discharge then increases in a considerable 

 degree, different for every gas and greater in proportion as the con- 

 ductibility of the gas is weaker. They have besides, observed that 

 the condensation of the luminous jet is accompanied by a real 

 condensation of the gas in the part in which the magnet acts. This 

 can explain, to a certain extent at least, the observations made by M. 

 Chautard upon the modifications of the spectrum of gases under the 

 action of magnetism. This fact is easily proved by means of a special 

 Geissler's tube, divided into two chambers, both traversed by the same 

 discharge, one of which is placed under the influence of the magnet, 

 the other not. These two compartments being separated by the 

 turning of a cock whilst the discharge is passing, it will be afterwards 

 found that there is a greater pressure in the compartment placed 

 between the two poles of the magnet than in the other. 



A very brilliant experiment made about thirty years ago by A. de la 



