GENERAL SCIENCE 



CHAPTER I 



HEAT 



1. Value of Fire. Every day, uncontrolled fire wipes out 

 human lives and destroys vast amounts of property ; every 

 day, fire, controlled and regulated in stove and furnace, cooks 

 our food and warms our houses. Fire melts ore and allows 

 of the forging of iron, as in the blacksmith's shop, and of the 

 fashioning of innumerable objects serviceable to man. Heated 

 boilers change water into the steam which drives our engines 

 on land and sea. Heat causes rain and wind, fog and cloud; 

 heat enables vegetation to grow and thus indirectly provides 

 our food. Whether heat comes directly from the sun or from 

 artificial sources such as coal, wood, oil, or electricity, it is 

 vitally connected with our daily life, and for this reason the 

 facts and theories relative to it are among the most important 

 that can be studied. Heat, if properly regulated and con- 

 trolled, would never be injurious to man ; hence in the follow- 

 ing paragraphs heat will be considered merely in its helpful 

 capacity. 



2. General Effect of Heat. Expansion and Contraction. 

 One of the best-known effects of heat is the change which 

 it causes in the size of a substance. Every housewife knows 

 that if a kettle is filled with cold water to begin with, there 

 will be an overflow as soon as the water becomes heated. 

 Heat causes not only water, but all other liquids, to occupy 



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