Mr. J. Gill on the Dynamical Theory of Heat. 369 



form carbonic oxide and carbonic acid in the act of combustion, 

 the particles must be brought so close together as to come within 

 the spheres of chemical attraction under the influence of which 

 they unite. It would be difficult to effect this approximation of 

 the particles by gradually squeezing together the two bodies in 

 mass, as general molecular repulsion increases to a powerful 

 degree under the compression of matter; but in electricity and 

 heat we possess agencies which, operating directly on the indivi- 

 dual particles of matter, can produce results of intensity of action 

 incomparably more powerful than can be effected by any mecha- 

 nical means which can be brought to bear on masses. Thus 

 the friction of a chemical match, by concentrating the mecha- 

 nical action, is sufficient at a few points of actual molecular con- 

 tact to generate a very high local temperature, which throws 

 the excited particles into such violent molecular motion as to 

 impel them over the boundaries of repulsion fairly within the 

 sphere of chemical attraction. Under the influence of this force 

 they combine with intense atomic action, which, communicating 

 from particle to particle, causes the rapid lighting of the whole 

 mass ; and by the same play of molecular movements the phe- 

 nomena of fire or flame may be supposed to originate, from the 

 burning of the humblest rushlight to the most destructive con- 

 flagration. 



The intense vibratory or orbital motions of the compound par- 

 ticles formed in the act of combustion constitute the heat or 

 temperature of the flame, while solid particles of carbon, ren- 

 dered incandescent by the highly excited atmospheres in which 

 they are enveloped, are supposed to increase its luminosity, 

 giving consistence and body to the fainter light of the glowing- 

 gases. The attraction of chemical affinity no longer exists 

 between the homogeneous compound particles resulting from 

 the combustion, and they are now under the uncontrolled influ- 

 ence of common molecular repulsion, which tends to separate the 

 particles, increasing in intensity in some geometrical ratio of the 

 inverse distances. 



In the case of gunpowder and other explosive compounds, in 

 the solid form containing in themselves the elements whose 

 combination gives rise to the phenomena of combustion, the 

 action of the chemical forces can take place in a confined space, 

 and the accompanying repulsion, resulting from both the tem- 

 porary heat and the permanent expansion of the resulting gases, 

 may be availed of as a direct dynamical agent not only in impel- 

 ling projectiles, but also in giving motion to a piston acting 

 in a cylinder like that of a steam-engine. The same result 

 can be obtained from the close combustion of explosive gaseous 

 mixtures; and a considerable amount of power can be made 



