128 Common Science 



radiating away until the sun brings us more heat the 

 next day, it is colder just before dawn than at midnight, 

 more heat having radiated into space. 



For the same reason it is colder in January and Febru- 

 ary than in December. It is in December that the days 

 are shortest and the sun shines on us at the greatest 

 slant, so that we get the least heat from it ; but we still 

 have left some of the heat that was absorbed in the 

 summer. And we keep losing this heat by radiation 

 faster than we get heat from the sun, until almost spring. 



Application 33. Distinguish between radiant and con- 

 ducted heat in each of the following examples : 



(a) The sun warms a room through the window, (b) A 

 room is cooler with the shades down than up, when the sun 

 shines on the window, (c) But even with the shades down 

 a room on the sunny side of the house is warmer than a room 

 on the shady side, (d) When a mirror is facing the sun, the 

 back gets hot. (e) If you put your hand in front of a mirror 

 held in the sun, the mirror reflects heat to your hand. (/) If 

 you put a plate on a steam radiator, the top of the plate 

 gradually becomes hot. (g) If anything very hot or cold 

 touches a gold or amalgam filling of a sensitive tooth, you 

 feel it decidedly, (h) The handle of your soup spoon be- 

 comes hot when the bowl of it is in the hot soup, (f) The 

 moon is now very cold, although it probably was once very 

 hot. 



Inference Exercise 

 Explain the following : 



181. Trees bend in the wind, then straighten up again. Why do 



they straighten up ? 



182. A cloth saturated with kerosene and placed in the bottom of 



a clock will oil the clockworks above it. 



183. In cold weather the doorknob inside the front door is cold. 



184. It is cool in the shade. 



