EFFECTS OF HEAT 71 



To mark the scale, the bulb is put into ice, and the point to 

 which the mercury rises is marked ; the bulb is then put into 

 steam or boiling water, and the point to which the mercury rises is 

 marked 100. The space between is then divided into equal parts, 

 and the marks may be continued above 100 and below 0. This 

 gives a Centigrade scale. How would the marking of a Fahrenheit 

 scale differ from this? 



QUESTIONS 



1. State the theory of heat. Give examples which seem to 

 show the truth of this. 



2. What is the great source of heat upon earth? Can you 

 show how the heat from coal once came from the sun ? 



3. What is meant by cold? Is any body absolutely cold? If 

 a body were entirely cold, what would be the condition of its 

 molecules ? 



4. Define temperature. Carefully explain the difference between 

 temperature and quantity of heat. 



5. For what is a thermometer used? Explain how the ther- 

 mometer is made and how it acts. 



6. What two thermometers are in common use ? Which one 

 do we use daily? What is the standard in each? On which 

 scale are the degrees the shorter? 



7. Name and describe the more common sources of heat. 



SECTION II 

 EFFECTS OF HEAT 



80. The Effects named. In general, the effects of 

 applying heat to bodies are four in number, chemical 

 effects, electrical effects, changes of volume, arid changes 

 of state. The first two of these effects will be treated in 

 later chapters ; we shall now consider only changes of vol- 

 ume and of state which are caused by the action of heat. 



