166 Intelligence and Miscellaneous Articles. 



I passed the current through the apparatus and through a tan- 

 gent-compass, which at the first moment indicated an intensity^. The 

 apparatus was then removed and replaced by coils of known resist- 

 ance, and by a rheostat the length of which could be varied so as to 

 reproduce the intensity i. The resistance of the liquid was equal to 

 that of the coils and of the rheostat. 



The numbers obtained are the following ; they are inversely as 

 the conducting-power of the liquid : — 



Liquids. Turns of rheostat. Conductivity. 



Water „ 55 1000 



Petroleum 765 72 



Sulphide of carbon 1000 55 



Alcohol 1130 49 



Ether 1375 40 



Oil of turpentine 2380 23 



Benzole 34S0 16 



— Comptes Rendus, June 28, 1869. 



ON THE HEAT DEVELOPED IN DISCONTINUOUS CURRENTS. 

 BY MM. JAMIN AND ROGER. 



Pouillet has shown that when a current of the intensity I is passed 

 into a short rectilinear circuit which developes no phenomena of 

 induction, and which is broken at very short and regular intervals 

 by a vibrating apparatus, the tangent-compass exhibits an apparent 

 intensity I r This intensity is equal to I diminished in the ratio 

 of the time a, during which the current passes, to the duration I of 

 one vibration of the break, so that we have 



We may infer from this result that the broken current is made up 

 of successive fragments of currents which last during the time a, 

 and which have a real intensity I, and that there is no change either 

 at the moment of making or of breaking each. 



On the other hand, we know r that, according to Joule, the amount 

 of heat, C, disengaged in the unit of time in each resistance r, by a 

 current having the intensity I, is proportional to this resistance rand 

 to the square I 2 of this intensity ; it is equal to KrI 2 , K being a con- 

 stant. This law has been found to hold good for continuous cur- 

 rents ; we have investigated whether it holds in the case of broken 

 currents. 



For this purpose we passed these currents through a thermorheo- 

 meter, an instrument which one of us devised, and which was laid 

 before the Academy on the 6th of July 1868. It consists essen- 

 tially of a fine platinum wire, the length of which may be varied, 

 and which is immersed in the reservoir of a thermometer in the 

 middle of an isolating liquid. The heat developed by the current 

 is transmitted to this liquid, and is measured by the expansion ob- 

 served. Operating in this manner, we have ascertained that broken 

 currents always develope more heat than continuous currents of the 

 same apparent intensity, I x . 



This fact does not contradict Joule's law ; we shall, on the con- 

 trary, see that, when generalized, it justifies the ideas of Pouillet. For 



