OBJECTS.] INTRODUCTORY. 63 



hydrogen, with 224-^ grains of oxygen, and nothing 

 else. (See 50.) 



As there is not the slightest difference in weight 

 between a given quantity of water and the ice, or the 

 steam, into which it may be converted, it is clear that 

 the heat which is added to or taken from the water to 

 give rise to these several states, can possess no weight. 

 If then heat is a material body, it must be devoid 

 of weight and hence, in former times, heat was 

 called an imponderable substance. It was thought 

 to be a kind of fluid, called caloric, which had no 

 weight, and which drove the particles of bodies 

 asunder, when it entered them as they were heated, 

 and let them come together as it left and they grew 

 cool. 



45. The Phenomena of Heat are the 

 Effects of a rapid Motion of the Particles 

 of Matter. 



This much, however, is certain : that heat can be 

 caused by motion. Every boyknows that a metalbutton 

 may be made quite hot by rubbing it. A skilful smith 

 will hammer a piece of iron red hot. The axles of 

 wheels become red hot by rubbing against their bear- 

 ings, if they are not properly lubricated ; and even two 

 pieces of ice may be melted by the heat evolved when 

 they are rubbed together. And there are abundant 

 other reasons, as you will find when you study physics, 

 for the belief that the sensation we call heat, and all 

 the phenomena which we ascribe to heat, are the effects 

 of the rapid motion of matter. 



However, a quiescent body may be made hot with- 

 out exhibiting the least appearance of motion. The 



