SOURCES OF HEAT. 29 



What is said 51. HEAT OF THE FIXED STARS. The 



of the heat of 



fixed stars? fixed stars are suns of other systems, and 

 sources of heat, like our own sun. And their number 

 is so great, that notwithstanding their distance, they 

 exert a very important eifect on the temperature of 

 the earth. It is estimated that they give us nearly as 

 much heat as the sun, and that without this addition to 

 the sun's heat, neither animal nor vegetable life could 

 exist upon the earth. 



52. HEAT OF CHEMICAL ACTION AND 



Give examples 



of heat pro- ELECTRICITY. We shall see hereafter that 



mic'al ^action heat ls evolved in almost al * Cases of che- 



and by elcc.tri- mical action. Indeed, the heat of our fires 

 has this origin, as will be explained in an- 

 other chapter. The heat of the lightning is devel- 

 oped by electricity. 



Give examples 53. HEAT FROM FRICTION. The heat 



f jj*j* P produced by slight rubbing is sufficient to 

 tion. set on fire a phosphorus match. Sir 



Humphrey Davy produced heat by friction between 

 two pieces of ice. It is said that Indians produce fire 

 by rubbing two sticks of wood together. Count Rum- 

 ford caused water to boil by boring a cannon beneath its 

 surface. These are all cases of the production of heat 

 by friction. 



