CHAPTER VIII 



WEATHEK AND CLIMATE 



The Warming of the Atmosphere. The sun trans- 

 mits both light and heat to the surface of the earth through 

 the atmosphere. On the top of a high mountain the tem- 

 perature is found to be colder than on the lower levels. 

 The amount of sun radiation, technically called insolation, 

 that falls upon a given surface on the mountain is about 

 the same as that which falls upon an equal surface in the 

 valley. If the heating effect is 

 less it must be due to something 

 besides the number of heat rays 

 intercepted. FIGURE 83 



In the spring when gardeners 



wish to hurry the growth of their plants, they cover them 

 with boxes, the tops of which are made of glass (Figure 83). 

 It is found that the temperature within the boxes is higher 

 than that outside. 



The high temperature heat rays coming from the sun 

 pass readily through the glass and are absorbed by the 

 ground within the box, raising its temperature. The ground 

 continues to keep warm after the sun ceases to shine because 

 the heat given off by the soil under the box cannot readily 

 pass out through the glass. Thus the heat of the sun is in 

 a certain sense entrapped in the box or cold frame. 



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