244 Prof. De la Rive on the Propagation of Electricity 



results which I have succeeded in obtaining while studying the 

 propagation of electricity in metallic vapours, and which, although 

 still far from complete, are not without interest. But previously 

 it is necessary that I should shortly indicate the process which I 

 have employed in my experiments for generating and for mea- 

 suring the electricity. 



The electricity is produced by means of a RuhmkorfPs appa- 

 ratus of moderate power, worked by two Grove's cells of large 

 surface, and a contact-breaker of the ordinary construction. It 

 is true that the electricity thus produced consists of two dis- 

 charges successively in opposite directions; hence, if the circuit 

 •which the discharges have to traverse is composed of good con- 

 ductors only, such as metallic wires, or even distilled water, no 

 deflection is produced by them on a galvanometer, since, the cur* 

 rents being alternately of equal intensity in opposite directions, 

 and succeeding each other very rapidly, the effect of their joint 

 action is that they neutralize one another. But if the circuit 

 contains an elastic fluid, even very much rarefied, the resistance 

 which this fluid opposes to the passage of the two successive 

 discharges causes one of them to predominate, so that the result- 

 ing phenomena are such as would be produced by a series of 

 discharges all taking place in the same direction. This differ- 

 ence arises from the mode of construction of the [apparatus, 

 which causes the two induced currents, though equal to each 

 other in quantity, to be of unequal tension ; so that when an 

 imperfect conductor, such as a gas more or less rarefied, is placed 

 in the circuit, only one of the currents is transmitted (or at least 

 it is transmitted in much greater force than the other) , and hence 

 the series of currents have all one and the same direction. 



In order to measure the intensity of the transmitted currents, 

 a glass trough, 20 centims. long by 5 wide and 3 deep, contain- 

 ing distilled water, is placed in the circuit which they are required 

 to traverse ; two platinum plates, fixed one at each end of the 

 trough and having a surface exactly equal to the transverse sec- 

 tion of the water, serve to establish a connexion between this 

 water and the rest of the circuit. Two platinum wires inserted 

 into glass tubes are held vertically by firm supports, so that their 

 lower ends dip into the distilled water — these ends projecting 

 only a millimetre beyond the glass, so as to form a pair of " Wol- 

 laston's points/'' — while the upper ends are connected with the 

 two terminals of a galvanometer the wire of which is well insu- 

 lated. The supports which hold the platinum wires are moveable 

 along a divided scale; so that the ends which dip into the water 

 can be brought as near together as possible, or can be separated 

 by nearly the whole length of the trough. The distance between 

 the platinum-points is regulated by a micrometer-screw, and is 



