LECTURE VI. 

 EXPERIMENTAlTPHILOSOPHY. 



OF PNEUMATICS. 



THE air we breathe is an heterogeneous mix- 

 ture, that is, a matter composed of different sub- 

 stances, and not of particles of perfectly the 

 same nature. This is one of the secrets which 

 the wonderful discoveries of modern chemistry 

 have revealed to us. According to this system, 

 caloric, or the matter of fire, is the basis of all 

 fluidity, and therefore air may be considered as 

 consisting of very minute particles, which swim, 

 or are suspended in a mass of that very subtile 

 and active fluid. The properties of caloric are 

 not, however, perceptible in this mixture ; for on 

 account of the attraction which subsists between 

 those particles of which air is composed, and 

 those of caloric, the latter is rendered latent, as 

 Dr. Black expresses it, or, in other words, in- 

 active. The matter of atmospheric air is therer 

 fore composed of caloric as its basis, and some 

 other matters. Or the other matters may be 

 considered as dissolved and floating in the mass 

 of fire, like salt, or gum, or any other substance 

 in water. The nature of these matters will be 

 explained in the chemical lectures, and would be 



