260 Prof. Wartmann on the Cooling of Electrified Bodies. 



3. On the Cooling of Electrified Bodies*. 



It is perhaps impossible to isolate the effects of any one of 

 the imponderable fluids in an absolute manner, and in parti- 

 cular those of electricity and of heat. It is interesting to search 

 o«t the relations which connect these two universal agents, as 

 well in order that our speculations on their nature may be 

 rendered more conformable to experimental truth, and on ac- 

 count of the part that each of them tends to play in the ceco- 

 nomical applications of the other. 



In some recent researches I endeavoured to prove that elec- 

 tricity is not of itself hotf. On the basis of this fact I now 

 purpose to prove that the velocity with which a body cools is 

 independent of the state of electric tension of its surface or of the 

 surrounding matter, all other circumstances being constant. 

 Let us first examine non-porous bodies. A cylindrical vessel 

 of polished tin-plate, supported in a horizontal position by a 

 strong pillar of glass varnished with gum-lac, was filled with 

 boiling water. The orifice was immediately closed with wad- 

 ding, surrounding a thermometer with a long cylindrical reser- 

 voir and entirely mounted in glass. The descent of the 

 mercury might be observed by means of a telescope placed at 

 the distance of ten feet, and the time taken for each degree of 

 cooling reckoned by means of a good seconds pendulum by 

 Ferdinand Berthoud. 



Numerous experiments have been made under circum- 

 stances of atmospheric pressure, of temperature and of hu- 

 midity, very nearly identical ; care was taken to eliminate the 

 effects of the heating by conduction or by radiation from the 

 supports and communicating rods. These experiments lead 

 to a remarkable equality of the time occupied by the re- 

 frigeration of the metallic vessel to the amount of several cen- 

 tigrade degrees, whether or not the vessel were placed in re- 

 lation with the conductor of an electrical machine, the plate 

 of which was O m, 87 in diameter, and which, making one turn 

 in a second, sustains the moveable branch of a pith-ball elec- 

 troscope at an angle of 145° with the vertical. Here are the 

 results of three series of trials : — 



Height of the barometer O m -7201 



Interior temperature + 20 0, 4 C 



Exterior (Hair) hygrometer . . . . 80° 



* Read before the Helvetian Society of Natural Sciences, sitting at 

 Lausanne, 26th July, 1843; and now communicated by the Author, 

 t Archives of Electricity, vol. i. p. 603 [see ante, p. 257]. 



