Fire and Heat 



93 



higher in summer or in winter? Of a suspension bridge? Explain. 

 5. A party is being equipped for Arctic exploration. What kind of 

 a thermometer and barometer should be taken? Explain. 6. Men- 

 tion several practical uses of our ability to obtain unusually high and 

 low temperatures. 7. Mention several industries in which exact meas- 

 urement of temperature is indispensable. Give reasons. 8. Would ex- 

 act measurement and control of temperature in baking or roasting 

 foods be advantageous? In what ways? 



IV. How HEAT Is TRANSFERRED 



Heat produced by burning fuel in a range is transferred to 

 other bodies in several ways (Fig. 27). The range and cooking 

 utensils placed upon it are heated in one way. The water in 

 the teakettle or the hot-water tank is 

 heated in another way, as is also the air 

 of the room. Objects which are exposed 

 to, but not in contact with, the range 

 are heated in a third way, as may be 

 seen when some article is injured by 

 being left too near the fire. The three 

 ways in which heat is transferred from 

 its source to other objects are now to be 

 studied in some detail. 



41. Conduction. First of all, heat, FlG 27 ._ Three ways 

 as you know, is transferred from the fire of transfer of heat. Con- 



duction 



convection 



or range to objects in contact with it. > . radiation 



What happens to an iron poker when it Explain how each is 

 is held with one end in the fire? Will it brou s ht about - 

 finally become too hot to hold in the bare hand? Does the 

 heat travel visibly from one end to the other? You know 

 that the poker is heated throughout its length, or, as it is 

 commonly described, the heat is conducted by the metal. So 

 with the utensils on the top of the range. Heat is conducted 

 from the fire by the range and by the utensils. As all substances 

 are composed of countless minute particles, it is assumed that 

 each particle transmits to its neighbor the heat it receives, 



