44 AX8WEJSS TO PRACTICAL QUESTIONS 



34. Does stirring the ground arotind plants aid in the depo- 

 sition of dew? 



It does, since it facilitates radiation. 



35. Why does the snow at the foot of a tree melt sooner than 

 that in the open field? 



The dark-colored tree absorbs the sun's heat, and then 

 radiates it out in slow, dull waves, which are absorbed by the 

 snow. 



36. Why is the opening in a chimney made to decrease in 

 size from bottom to top ? 



Because as the heated air rises it cools and shrinks. If the 

 chimney did not diminish in size correspondingly, currents of 

 cold air would set down from the top. 



37. Will tea keep hot longer in a bright or in a dull tea-pot * 

 In a bright one, since a polished surface retards radiation. 



39. Why is one's breath visible on a cold day ? 



The vapor in the breath is condensed by the cold air. 



41. Why is light-colored clothing cooler in summer and 

 warmer in winter than dark-colored? 



It does not absorb the heat of the. sun in summer, nor the 

 heat of the body in winter; dark- colored clothing has neither 

 of these desirable properties. 



42. How does the heat at two feet from the fire compare 

 with that at four feet ? 



2 2 : 4 2 : : 1 : 4. 

 Hence it is four times greater. 



43. Why does the frost remain later in the morning upon 

 some objects than upon others ? 



Those objects which are good absorbers of heat soon become 

 warm enough to melt the frost upon them : "poor absorbers 

 heat more slowly, and so retain the frost longer. 



44. Is it economy to use green wood ? 



It is not, since the sap must be changed to vapor, and watei 



