1857.] The Heat Force. 453 



gestions of research and discovery which arise from it*. Heat, 

 for instance, is a mighty form of power, and its effects have 

 been greatly developed ; therefore, assumptions regarding its 

 nature become useful and necessary, and philosophers try to 

 define it. The most probable assumption is, that it is a mo- 

 tion of the particles of matter ; but a view, at one time very 

 popular, is, that it consists of a particular fluid of heat. 

 Whether it be viewed in one way or the other, the principle of 

 conservation is admitted, I believe, with all its force. When 

 transferred from one portion to another portion of like matter, 

 the full amount of heat appears. When transferred to matter 

 of another kind, an apparent excess or deficiency often results'; 

 the word " capacity " is then introduced, which, whilst it ac- 

 knowledges the principle of conservation, leaves space for re- 

 search. When employed in changing the state of bodies, the 

 appearance and disappearance of the heat is provided for con- 

 sistently by the assumption of enlarged or diminished motion, 

 or else space is left by the term " capacity" for the partial views 

 which remain to be developed. When converted into me- 

 chanical force, in the steam- or air-engine, and so brought into 

 direct contact with gravity, being then easily placed in rela- 

 tion to it, still the conservation of force is fully respected and 

 wonderfully sustained. The constant amount of heat developed 

 in the whole of a voltaic current described by M. P. A. Favref , 

 and the present state of the knowledge of thermo-electricity, 

 are again fine partial or subordinate illustrations of the prin- 

 ciple of conservation. Even when rendered radiant, and for the 

 time giving no trace or signs of ordinary heat action, the as- 

 sumptions regarding its nature have provided for the belief in 

 the conservation of force, by admitting, either that it throws 

 the ether into an equivalent state, in sustaining which for the 

 time the power is engaged ; or else, that the motion of the 

 particles of heat is employed altogether in their own transit 

 from place to place. 



It is true that heat often becomes evident or insensible in a 

 manner unknown to us ; and we have a right to ask what is 

 happening when the heat disappears in one part, as of the 



* Helmholtz, " On the Conservation of Force." Taylor's ' Scientific Me- 

 moirs/ 2nd series, 1853, p. 114. 

 t Comptes Rendus, 1854, vol. xxxix. p. 1212. 



