WEATHER AND CLIMATE n 



Standing also on the top of our hill we remember that there 

 are hills even higher than Mt. Blanc, and that the highest of 

 these have not yet been climbed, because it gets colder and colder 

 and more and more difficult to breathe as the climber ascends, 

 until he finds it impossible to go farther. We conclude then that 

 if the air gets thinner and thinner as we ascend, there probably 

 comes a time when there is no more air, and if it gets colder and 

 colder as we go up it will be probably very cold in the region 

 where the air disappears. Thus we reach the provisional conclusion 

 that the air has something to do with making the earth warm. 



In going farther one must be careful not to attempt too much, 

 for the problems involved are of course highly complex. A few 

 simple points should, however, be emphasised. It is so cold on 

 the top of high hills, in spite of the strong sun, that the snow never 

 completely melts. It is cold also when people ascend in balloons, 

 and colder still when they send kites up to heights they cannot 

 reach. Therefore, though the sun sends his rays through space, 

 those rays are not warm till they reach the earth, and it is the warm 

 earth, not directly the sun, which warms the air. But the air 

 acts like a blanket and prevents the loss of the warmth which the 

 earth is always radiating into it. One of the reasons why it is cold 

 on the mountain tops is that there the blanket of air is thin. Air, 

 especially if it is dry, allows the rays which make the earth warm 

 to pass through it easily, but, as we have already seen, damp air 

 stops some of the rays, and therefore, other things being equal, 

 damp days feel colder than dry ones. 



When the sun shines then we have to think of the rays pouring 

 through space, pouring through our thick blanket of air, and 

 warming the upper surfaces of the soil. The warm soil again 

 throws back its heat into the air, and warms its lower layers. If 

 the soil is dry it warms the air much more than if it is moist, for then, 

 as we shall see, some of the heat is used for another purpose. 



On our excursions an opportunity should be taken to read the 

 thermometer first in the shade on the bank of a pool or stream, 

 and then when its bulb is plunged beneath the surface of the water. 

 We shall of course find by the thermometer what we already know 

 by our own feelings, that the water is colder than the ground or the 

 air, though the same sun is shining on both. We notice, then, that 



