AGRICULTURE WITH CHEMISTRY. 



19 



HEAT. 



By heat is to be understood the sensation arising 

 from the solar rays, or from the combustion of inflam- 

 mable bodies. Combustion cannot take place without 

 the presence of air, and it is only the vital part of air 

 that promotes this process. A certain degree of heat is 

 requisite for animal and vegetable life. It is generated 

 in animals, in consequence of respiration, by the ab- 

 sorption of the vital part of atmospheric air, and com- 

 bination thereof with the animal system ; here called the 

 process of animal oxygenation : and as animals have thus 

 the power of generating heat by respiration, they can 

 live in a much greater degree of cold than vegetables. 



To the presence of heat is to be ascribed the fluidity 

 of water ; to the absence of it, its solidity, or the forma- 

 tion of ice. 



The principle of heat is contained in bodies Mithout 

 sensibly manifesting its presence; it is then called latent 



c 2 heat. 



