CHAPTER VIII 

 SOME APPLICATIONS OF HEAT 



After man had discovered fire it took him ages to learn 

 to control the heat energy fire created, and so to make it a 

 servant to warm his home and to supply force to help build 

 and drive great machines. 



Heat, man found, showed a great tendency to escape 

 from its source. It might seemingly leap from the fire to 

 scorch his face, yet leave his back chilled. It might travel 

 the length of a crude iron bar, from the end in the flame, 

 and burn his hand. It might actually flow about his hut 

 in currents, or might flow upward and escape through a 

 roof opening, leaving him unwarmed. 



First, man built his fire on the ground. Then he in- 

 vented an open fireplace and chimney, and after centuries 

 he designed stoves to hold his fire for cooking and for 

 warmth. Finally, using the tendency of certain heated 

 matter to flow, and of other matter to radiate heat, he 

 learned to build his fire in a furnace and pipe heat in the 

 form of hot air, water and steam in quantities both large 

 and small to provide for the heating of all types of build- 

 ings. All these improvements resulted from a knowledge 

 of the laws of matter and energy as related to heat. 



Heat is energy resulting from the motion of molecules. This 

 motion is passed on from molecule to molecule and from object 

 to object, and tends to diffuse, or spread out, until the places and 

 objects where heat is present have the same temperature. You 

 have undoubtedly noticed that when your hand is cold it becomes 

 warmer by taking hold of an object which is warm. The heat 

 moves from the object into your hand. If matter having a low 

 temperature is placed in warm surroundings, it will absorb heat 

 until it becomes as warm as the other objects around it. 



Ways in Which Heat Moves. Heat moves or is trans- 

 ferred from object to object in three ways : by radiation, that is, 

 by passing in straight lines through space from one object to 



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