that Electricity does not contain heat. 259 



the form of a straight prism with a square base m, 14 long 

 by O m, 01 in width, formed of one-half bismuth and one-half 

 antimony. Two little hollows made near its extremities 

 were filled with mercury, in order to secure perfect con- 

 tact with the rheometric wire. The deviation of the needle 

 remained null, even after the thundering discharge of a bat- 

 tery of eight great jars, charged by 125 turns of a machine 

 the plate of which is nearly a metre in diameter, and which 

 usually gives sparks at six centimetres. Now here there 

 was but one soldering, and the apparatus was so sensible that 

 the contact of the finger during two or three seconds pro- 

 jected the needle to 90°. 



Electricity then is not hot of itself; its thermic effects pro- 

 ceed only from the obstruction which the conductors oppose 

 to its passage. This conclusion, which appears very natural 

 to me, is interesting on account of the assimilation which may 

 be made by its means with the results to which the study of 

 the diathermancy of voltaic couples leads us. The thermo- 

 electric element employed is the very same as that by the aid 

 of which I repeat in my lectures the experiment of cold pro- 

 duced at the soldering of two metals, fractured by the passage 

 of a voltaic current *. As in all other physical actions, we 

 here perceive the influence of time. An electrical discharge, 

 be it ever so powerful, does not give heat, because it is instan- 

 taneous ; a current on the contrary produces an elevation or 

 depression of temperature, because it is continued, and its du- 

 ration allows and produces changes in the statical condition 

 of the molecules of the heterogeneous conductor at the surface 

 of the soldering. 



We arrive at the same conclusion with an air-thermometer, 

 the glass bulb of which is at the same time very thin and of 

 great dimensions, and its tube capillary. If sparks from the ma- 

 chine or discharges of a jar are made to fall upon the bulb, no 

 depression of the liquid column is observed, whether the glass 

 of the bulb be naked f or covered with a conducting armature, 

 such as tinfoil. But when the bulb is covered with lamp-black 

 or powdered resin, a heating is perceptible, due to the insu- 

 lating property and to the combustion of the clothing sub- 

 stance. 



Lausanne, Nov. 30, 1842. 



* Arch, de FElectr., t. i. p. 74. Mem. de la Soc. de Phys. et cFHist. 

 Nat. de Geneve, t. ix. 



f I attribute the slight rise which sometimes takes place to the cold 

 produced by the evaporation, under the electric influence, of the pellicle 

 of vapour adhering to the glass. 



S2 



