THE FORMATION OF CLOUDS. 



499 



found at the ground in the polar regions during the coldest days of 

 winter^ The obvious correction for the suffering of humanity due to 

 the oppressive hot waves of summer is to bring down this upper air, or 

 else arrange to visit it in floating houses. 



The reader may have noticed that hail falls usually in the summer 

 instead of in the winter, and have wondered what is the reason for it. 

 The answer is simple. If we arrange a diagram so that freezing tem- 

 perature is on the left and 100 degrees Fahrenheit on the right, and 

 plot the limits of the rain, hail and snow regions in altitude, the result 

 is shown in a set of curves which indicate the height at which it is 

 possible for them to form respectively. In the summer when the 



Chart 3. Distribution of rain, hail and snow in the atmosphere according to the tempera- 

 ture and height of formation. The curves mark the average boundaries of the several stages of 

 the moisture in the atmosphere. 



weather is warm there is more moisture in the air, it rises higher, till 

 in extreme cases it may reach about seven or eight miles. The stages 

 each become wider, though the hail is always confined to a narrow wedge- 

 shaped region whose highest place is about four miles. Now in thunder- 

 storms when there is powerful congestion and stratification of air cur- 

 rents in a vertical direction, the conditions are favorable for the form- 

 ing of snow balls first by congealing the flakes in the lower parts of the 

 upper stage; these fall slowly through the freezing stage and are 

 coated with a layer of ice; they drop through the rain stage and col- 

 lect a thicker covering of ice till they arrive at the ground as hail- 

 stones. Such strata may be intermixed and arranged in alternate 

 layers so that a nucleus of snow may fall through more than one pair 

 of snow and freezing regions in succession, and thus cover itself with 

 several layers of snow and ice, like an onion. Such stratified hail- 

 stones are often found when they are cut open. This theory seems to 



