368 Mr. J. Gill on the Dynamical Theory of Heat. 



in quantity equivalent to the force which had been expended in 

 producing the tension. 



It seems impossible to form any satisfactory idea of the 

 nature of the forces of attraction and repulsion ; and after ages 

 of research by intellects of the highest order the subject still 

 remains enveloped in mystery. Chemical forces seem to be spe- 

 cific properties inherent in matter; and the general forces of at- 

 traction and repulsion are by some considered as essential pro- 

 perties of ponderable matter, while others incline to attribute 

 them to the action of a more subtle fluid medium present in all 

 space, so that matter cannot be conceived of apart from the uni- 

 versal influence of this all-pervading fluid. The force or vis viva 

 of motion may be conceived of as resulting from an original 

 impression of mechanical power on matter at its creation, or as 

 a consequence of the action of potential energies of attraction 

 and repulsion resulting from primitive positions of disturbed 

 equilibrium, in which atoms and masses may have been placed 

 at their formation. 



The general sources from which we can derive ready-made 

 elemental power are the natural movements of the atmosphere 

 in the phenomena of the winds, and the fall of water under the 

 influence of common terrestrial gravitation. But it is often 

 more expedient to produce mechanical power by artificial means, 

 or by the arbitrary employment of the natural atomic forces of 

 inanimate matter ; and for this purpose we preferably avail our- 

 selves of the chemical forces, generally through the medium of 

 heat. In the combustion of common carbon fuels the heat is 

 supposed to arise from intensely active molecular motion caused 

 by the clashing of the oxygen atoms against those of the carbon, 

 in which process the rapid motion of translation of the excited 

 particles falling violently together under the influence of chemi- 

 cal attraction, is changed by the shock into intense molecular 

 motion of vibration, or orbital movements, or perhaps some mode 

 of individual expansion of the molecules, supposed to constitute 

 the phenomena of heat or temperature. This clashing of the 

 sympathetic particles in the act of combustion suggests the idea 

 of a forcible separation of the same elements at some former 

 period when the fuel was formed. Thus it is supposed that the 

 solar energy at some remote time in the history of creation, when 

 some of the common processes of nature were probably more 

 vigorous than we now perceive them, enabled the vegetative vital 

 principle in the ripe primeval productions of the teeming soil to 

 separate the carbon from the carbonic acid gas of the atmosphere, 

 and to assimilate it in a solid state in the gigantic grottoes of 

 the ancient forests of the carboniferous epoch. 



In order that the oxygen may combine with the carbon and 



