254 MOISTURE OE THE AIR; ITS FALL. 



clouds floating in the higher atmosphere, which 

 are only its first sources, but also from the lower 

 regions between them and the earth, the whole of 

 which contribute to its increase. A great differ- 

 ence may therefore be found between the amount 

 of rain which falls on the top of a mountain, or 

 even of a high tower, and that which is caught 

 during the same time at the foot of either. Thus 

 Dove tells us that the yearly rain-fall on the roof 

 of the Royal Palace at Berlin is eighteen inches 

 in depth, while that on the pavement of the 

 Palace-Place amounts to twenty inches. 



When the moist air in the upper regions is 

 cooled down below the freezing-point, the water 

 that it lets fall solidifies, and comes down as 

 Snow. It is often remarked that it rains on the 

 low-lying lands, while it is snowing on the moun- 

 tains. In such case, the rain was withdrawn from 

 the moist air as snow, which was melted during its 

 fall through the lower and warmer regions. This 

 thawing is often imperfect ; it then rains and 

 snows at once, or the snow-flakes, only softening, 

 cling together, and come down as Sleet, which 

 falls so often when the winter is passing into 

 spring. .Sleet is remarked in summer only on 

 high mountains. It is probable that Hail con- 

 sists of flakes of snow or sleet, which have been 

 formed in the upper regions, and round which, as, 

 in their fall, they passed through other mists 



