96 Introduction to the Study of Science 



imprison the air which immediately envelops the body and has the 

 same temperature as the body. They prevent the escape, except in 

 small measure, of bodily heat and keep the body comfortable in ex- 

 tremely cold or windy weather. Which will be safer, clothing of 

 cotton or of woolen goods, if soaked with water? Explain your 

 answer. Why do explorers in the Arctic regions use tents of silk? 

 Why do many persons place folded paper under their clothing in cold 

 or windy weather? 



The substances of which buildings are constructed are selected partly for 

 their poor conductivity of heat. Stone, brick, cement, glass, and wood 

 are poor conductors and make it practicable to maintain a very dif- 

 ferent temperature within a building than without. What is their 

 use in this respect in hot weather? In cold weather? 



Would a house built with double walls holding between them a 

 blanket of " dead " air be warmer in winter and cooler in summer than 

 if it were constructed with a single wall ? Explain. Would the double- 

 walled house be more rapidly heated in cold weather? What is the 

 advantage of wrapping steam or hot pipes with asbestos paper, or 

 painting them with asbestos paint? 



How are substances that are bad conductors of heat useful in 

 refrigeration ? How is ice kept in the ice house, or when being shipped ? 

 How may it be prevented from melting quickly in an ice chest? Ex- 

 amine a " fireless cooker." What is it that keeps the contents of the 

 cooker at a cooking temperature for a considerable period of time? 



Exercise : Sensations of temperature. Touch with the hand in 

 close succession several different kinds of substances in the same room 

 and apparently having the same temperature, such as woolen goods, 

 cotton, fur, wood, iron, oilcloth, tile, and marble. Are the sensations 

 of temperature the same? Fur and woolen goods feel warmer to the 

 touch than iron and marble. The explanation is based on their con- 

 ductivity of heat. Woolen goods either take no heat from the hand, 

 or give more heat to the hand than they receive ; consequently they 

 cause a sensation of warmth. Tile, oilcloth, marble, and the like 

 take up more heat than they give, with the result that one receives 

 from them a sensation of cold. Suppose now that the iron, marble, 

 and such substances have a temperature higher than that of the body. 

 Will they feel cold or warm ? Will they feel warmer than wood at 

 the same temperature? Explain this fact. 



42. Convection. -- The comforting fact is that air, which is 

 one of the poorest conductors of heat, can be heated by fire. 

 The water in the teakettle boils, and the water in the tank 



