218 SCIENCE OF COMMON THINGS. 



What is smoke ? Open fireplaces 111 adapted for heating rooms. 



1451 Which would prove the warmest upon a bed a blanket, or an 

 oiled silk, or India-rubber air-tight covering f 



The air-tight covering. 



1453 Why do we not use oiled silk or India-rubber bed coverings in 

 the winter ? 



Because they prevent ventilation, and, by shutting 

 in the insensible perspiration, soon produce dampness. 



1453 What is smoke? 



Small particles of carbon separated by combustion 

 from the fuel, but not consumed. 



1454 Is there a circulation of the air through the bed coverings at 

 night? 



Yes ; from every part of the bed-clothes immediately 

 over the person there is a constant outward oozing of 

 warm air, and an oozing inwards of cold air in lower 

 situations around. 



1455 In what two ways is heat communicated to apartments by fires 

 kept in them ? 



By radiation and immediate contact. 



The first portion passes through the air in diverging lines with great 

 velocity. The second penetrates slowly through the substance of the 

 densest bodies. To enjoy the full effect of radiated heat, we mus,t be in 

 the presence or sight of the radiating object. To receive conducted heat, 

 we must be in contact, either directly or through some intervening me- 

 dium, with the body that imparts it. 



1456 Does a person who sits by afire in the open air receive any heat 

 by conduction? 



Very little; for the air which surrounds the fire 

 having nothing to confine it, ascends by its diminished 

 specific gravity as fast as it is warmed, and its place is 

 immediately supplied by strata of cold air from beneath. 



1457 Will a person sitting beside a fire in the open air be exposed, 

 ipon the side of his body removed from the fire, to additional cold? 



He will, because cold currents rush in from every 

 nde towards the fire. 



1458 Why are open fireplaces ill adapted for the economical heating 

 ")f apartments ? 



In an open fireplace the air flows from the room to 

 the fire, becomes heated, and passes off directly into 

 the chimney, without having an opportunity of parting 



