Steam Engine. 41 
under different temperatures j it will be proper to describe 
briefly the method by which the Chemists account for 
the production of aeriform fluids. 
The term Caloric is used to denote the cause, whatever 
it may be, of hear, and of the phenomena which accompa- 
ny heat : it is now almost universally admitted to be a 
highly elastic fluid. Every body is according to its na- 
ture, capable of containing under a given volume a cer- 
tain quantity of caloric, either greater or less : this pro- 
perty was first observed by Dr. Black, and the English 
chemists designated it by the term Capacity of a body to 
contain the matter of heat. Professor Wilcke and M. 
Lavoisier first made use of the term specific caloric denot- 
ing by it the quantity of caloric respectively necessary to 
elevate to the same number of degrees the temperature of 
several bodies of equal weight. 
Substances volatilised and reduced to gas or aeriform 
fluids, are nothing else than ordinary solid or fluid bodies 
which by some circumstance are found superabundantly 
combined with caloric, in such a manner that the; consti- 
tuent particles of these bodies are separated the one from 
the other, by a quantity of ambient caloric much more 
considerable than that which surrounds the same particles 
in the natural state of the bodies. The extreme elasticity 
of the caloric the effect of which is augmented by its con- 
densation, and the weakening of the reciprocal attraction 
or of the cohesion of the particles of the bodies (a weaken- 
ing or diminution produced by the increased distance oi 
those particles) concur to diminish the density of the bo- 
dies in such a manner that they become reduced to an ae- 
riform state. 
As to the elasticity of gaseous fluids thus formed, it ap- 
pears in great measure to be produced by the. elasticity Oi 
caloric itself, which, when borlies are reduced to the gase- 
ous state ; occupy a very great part of their volume, 
ol IL * ,F 
