72 On the Production of Vapor. 



body approach each other, the. stronger will be their af- 

 finity. Every thing that tends to remove these integrant 

 parts .from each other, diminishes their affinity. Fire 

 produces this effect upon most known bodies. And it 

 not only diminishes their affinity, but being itself the 

 lightest of all substances, and rendering the bodies it 

 unites with more porous, it greatly increases their levity. 

 By the agency of fire, metals and ice are changed from 

 their natural solid state to that of a liquid. The power 

 of attraction is balanced by the opposite force of heat ; 

 the liquid state appears to be the point of the equilibrium 

 between these two forces. By increasing the heat, most 

 bodies are reduced to a state of gas. If we attend to the 

 method that nature pursues, we shall find, that water is 

 reduced to a state of vapor, and its texture is so altered 

 as to become specifically lighter than air, by the agency 

 of fire. Evaporation is, therefore, a dissolution of water 

 by fire. The various substances that compose the uni- 

 verse are, therefore, subjected to a general law on the 

 one hand, that tends to bring them together ; and to a 

 powerful agent on the other hand, which tends to remove 

 them from each other. It is upon the respective energy 

 of these two forces, that the consistence of all bodies de- 

 pends. Whether heat or caloric is truly possessed of a 

 repulsive principle, or whether it produces this effect 

 only by its endeavor to combine with bodies, forcing the 

 constituent particles to separate and recede from each 

 other, and diminishing their force of aggregation, I shall 

 not undertake to determine. A certain degree of affinity 

 exists between most substances and caloric, but this de- 

 gree in different substances is very various. It is there- 

 fore unequally dispersed in bodies, some absorbing and 

 retaining it in greater, and some in less quantities. By 

 contemplating the circumstances that attend its combi- 

 nation, we are led to conclude, that the component par- 

 ticles of bodies are surrounded with a caloric atmosphere 

 or investiture, more or less extensive, according to their 

 respective attraction. The parts of this atmosphere 

 more distant from the particle thus invested, being but 

 weakly attracted, will easily abandon it to restore an 

 equilibrium of heat, and will then become free or ther- 



