HEAT. 



ECTfON I. 



TEMPERATURE, THERMOMETERS, EXPANSION. 



472. Introductory Quotation." There are other forces 

 besides gravity, and one of the most active of these is chemical affin- 

 ity. Thus, for instance, an atom of oxygen has a very strong attrac- 

 tion for one of carbon, and we may compare these two atoms to the 

 earth and a stone lodged upon the top of a house. Within certain 

 limits, this attraction is intensly powerful, so that when an atom of 

 carbon and one of oxygen have been separated from each other, we 

 have a species of energy of position just as truly as when a stone 

 has been separated from the earth. Thus by having a large quan- 

 tity of oxygen and a large quantity of carbon in separate states, we 

 are in possession of a large store of energy of position. When we 

 allowed the stone and the earth to rush together, the energy of 

 position was transformed into that of actual motion ( 159), and we 

 should therefore expect something similar to happen when the 

 separated carbon and oxygen are allowed to rush together. This 

 takes place when we burn coal in our fires, and the primary result, 

 as far as energy is concerned, is the production of a large amount of 

 heat. We are, therefore", led to conjecture that heat may denote a 

 motion of particles on the small scale just as the rushing together of 

 the stone and the earth denotes a motion on the large. It thus 

 appears that we may have invisible molecular energy as well as 

 visible mechanical energy" Bcdfour Stewart. 



473. What is Heat tHeat is a form of en- 

 ergy. It consists of vibratory motions of the mole- 

 cules of matter or results from such motions, and 



