Preliminary Remarks. <9 



is applicable to the principle of magnetism, which manifests itself 

 in several metals. 



12. We have still less evidence of any thing material in the 

 principle of heat. Not only does it want, like the preceding, the 

 sensible properties by which matter is characterized, but the 

 laws of its motion and equilibrium, not being completely known, 

 we cannot arrive at the same probable conclusion, in this case as 

 in the former. By following it however in our experiments, we find 

 that it diffuses itself in bodies, passes from one to another, modifies 

 the disposition, the distances, and attractive properties of their 

 particles. But all this does not prove incontestibly, that the 

 principle in question is itself a body. The strongest argument 

 in favor of its materiality is derived perhaps from certain anal- 

 ogies, lately discovered, between the radiant properties of heat 

 and those of light, which lead us to believe that one of these 

 principles may change itself gradually into the other,' that 

 is, they may acquire and lose successively the modifications 

 by which they are respectively distinguished. The develope- 

 ment of these analogies furnishes a most important subject of in- 

 vestigation. 



1 3. It will be perceived from what has been said, that all 

 bodies of a sensible magnitude, the materiality of which can be 

 immediately determined, consist in the grouping together of a 

 multitude of material particles of extreme minuteness, in which 

 a difference in the mode of aggregation is the only circumstance 

 that constitutes a body solid, liquid, or gaseous. There are 

 moreover strong reasons for believing, as we have seen, that these 

 particles are inert masses, incapable from any inherent power 

 of their own, of modifying themselves, and susceptible only of 

 of obeying causes from without ; whether this want of choice and 

 self-direction is, in fact, as observation seems to prove, a general 

 and essential characteristic of matter, or whether we so regard 

 it intellectually for the purpose merely of considering by them- 

 selves those properties which remain to matter, after it is depriv- 

 ed of this. Now material particles being considered as in this 

 inert state, there will hence arise, in the phenomena which their 

 aggregation presents, certain necessary conditions, which are 

 applicable to all bodies, independently of the chemical nature 

 of their constituent parts, being the simple consequences of 



Mech. 



