462 On the two great powers, (Surr. 
admit heat, until it was so accumulated in rare bodies, that their elasti- 
city was superior in force to the cohesion of dense bodies, which is so 
far from being the case, that the elasticity of the atmosphere is eva- 
nescent in comparison with the cohesion of most solids. 
Secondly.—In his Elements of Chemistry Lavoisier proposed another 
explanation of the action of heat, in these words :—‘‘ It is perhaps more 
natural to suppose, that the particles of caloric have a stronger mutual 
attraction, than those of any other substance; and that these latter par- 
ticles are torn asunder, in consequence of this superior attraction of the 
particles of caloric, which forces them between the particles of other 
bodies, that they may be able to reunite with each other*.”’ 
This hypothesis, which treats of heat as a non-elastic substance, is 
liable to so many objections, that it has had very few advocates, and 
was probably relinquished by its great author. It is only necessary to 
remark one objection, which must have alone induced him to reject it. 
If the particles of heat had an attraction for each other so far superior 
to that apparent in the densest bodies, it is manifest; that it would not 
be diffused through all bodies, but would collect itself into masses abso- 
lutely dense, between the parts of which the atoms of no other bodies 
could possibly exist. 
Thirdly.—That doctrine of the nature and action of heat, which has 
been much received of late years, and which was introduced by Dr. 
CLEGHORN, is sosatisfactory, and conformed so nearly to the phenomena 
of the actions and motions of heat, that it may be considered as the 
true explanation. This doctrine, as is well known, considers heat as a 
body, whose particles are mutually repellent, but attract those of all 
other bodies, with various degrees of force. Hence its perfect elasti- 
city, and hence its presence in all bodies, but in various quantities in 
each. | 
Previously to making any further inquiry into the laws and action 
of heat, I propose to weigh the facts, which have been considered as 
objections to its materiality, and to state various arguments in proof of 
its materiality. 
The following facts have been at various times opposed to the 
material doctrine of heat: 
1. That, when many bodies are subjected to percussion, much heat 
is evolved. Iron may even be raised to a red heat. The explanation 
of this, which has been given by others, does not perhaps place the 
fact in quite so clear a light, as the following :—Since the force of 
cohesion in iron is very powerful, it is plain, that the heat between its 
* Elements of Chemistry, translated by Kerr, page 72. 
