132 HELMHOLTZ ON THE CONSERVATION OF FORCE. 



Berthollet*. The first of these assumptions lacks all experi- 

 mental proof; if it were true, then in the neighbourhood of the 

 rubbed portions a cold proportionate to the intense heat often 

 developed must be observed. The second assumption, without 

 dwelling upon the altogether improbable magnitude of action, 

 which according to it must be ascribed to the almost imperceptible 

 compression of the hydrostatic balance, breaks down completely 

 when it is applied to the friction of fluids, or to the experiments 

 where wedges of iron have been rendered red-hot and soft by ham- 

 mering and pieces of ice melted by friction t ; for here the softened 

 iron and the water of the melted ice could not remain in a com- 

 pressed condition. Besides this, the development of heat by the 

 motion of electricity proves that the quantity of heat can be ac- 

 tually increased. Passing by friction al and voltaic electricity — 

 because it might here be suspected that, by some hidden relation 

 of caloric to electricity, the former was transferred from the place 

 where it was originated and deposited in the heated wire — two 

 other ways of producing electric tensions by purely mechanic 

 agencies in which heat does not at all appear, are still open to 

 us, namely, by induction and by the motion of magnets. Sup- 

 pose we possess a completely insulated body positively electric 

 and which cannot part with its electricity ; an insulated con- 

 ductor brought near to it will show free +E, we can discharge 

 this upon the interior coating of a battery and remove the con- 

 ductor, which will then show — E ; this latter can of course be 

 discharged upon the exterior surface of the first or upon a second 

 battery. By repeating this process, it is evident that we can 

 charge a battery of any magnitude whatever as often as we please, 

 and by means of its discharge can develope heat, which nowhere 

 disappears. We shall, on the contrary, have consumed a certain 

 amount of force, for at each removal of the negatively-charged 

 conductor from the inducing body the attraction between both 

 is to be overcome. This process is essentially carried out when 

 the electrophorus is used to charge a Leyden jar. The same 

 takes place in magneto-electric machines; as long as magnet 

 and keeper are moved opposite to each other, electric currents 

 are excited which develope heat in the connecting wire ; and in- 



♦ Slatique Chimique, t. i. p. 247. 



t Humphry Davy, Essay on Heat, Light, and the Combinations of Light. 



