HELMHOLTZ ON THE CONSERVATION OP FORCE. 133 



asmuch as they constantly act in a sense contrary to the motion 

 of the keeper, they destroy a certain amount of mechanical force. 

 Here evidently heat ad infinitum may be developed by the 

 bodies constituting the machine, while it nowhere disappears. 

 That the magneto -electric current developes heat instead of cold, 

 in the portion of the spiral directly under the influence of the 

 magnet, Joule has endeavoured to prove experimentally *. From 

 these facts, it follows that the quantity of heat can be absolutely 

 increased by mechanical forces, that therefore calorific phaeno- 

 mena cannot be deduced from the hypothesis of a species of 

 matter, the mere presence of which produces the phaenomena, 

 but that they are to be referred to changes, to motions, either of 

 a peculiar species of matter, or of the ponderable or imponderable 

 bodies already known, for example of electricity or the lumini- 

 ferous aether. That which has been heretofore named the quan- 

 tity of heat, would, according to this, be the expression, first, 

 of the quantity of vis viva of the calorific motion, and, secondly, 

 of the quantity of those tensions between the atoms, which, by 

 changing the arrangement of the latter, such a motion can de- 

 velope. The first portion would correspond to that which has 

 been heretofore called free heat, the second with that which has 

 been named latent heat. If it be permitted to make an attempt 

 at rendering the idea of this motion still clearer, the view derived 

 from the hypothesis of Ampere seems best suited to the present 

 state of science. Let us imagine the bodies formed of atoms 

 which themselves are composed of subordinate particles (che- 

 mical elements, electricity, &c.), in such an atom three species 

 of motion may be distinguished, — 1, displacement of the centre 

 of gravity ; 2, rotation round the centre of gravity ; 3, displace- 

 ment of the particles of the atom among themselves. The two 

 first would be compensated by the forces of the neighbouring 

 atoms, and hence transmitted to these in the form of undulations, 

 a species of propagation which corresponds to the radiation of 

 heat, but not to its conduction. Motions of the single particles 

 of the atoms among themselves, would be compensated by the 

 forces existing within the atom, and would communicate motion 

 but slowly to the surrounding atoms, as a vibrating string sets 

 a second in motion and thereby loses an equal quantity of motion 

 ♦ Phil. Mag. S. 3. 1844. 

 SCIEN. MEM.— AW. Phil. Vol. I. Part II. L 



