SIGNS OF RAIK. 173 



direction, and soon melt into the air, it is a sure sign 

 that the lower stratum of the air is dry, and will 

 resist the descent of rain, even though the upper 

 part of the sky may be cloudy. But when, without 

 any high objects in their vicinity, some are inclined 

 one way and some another, there is disturbance in 

 the lower part of the air, and the probability is that 

 it will soon rain, even though at the time there be 

 not a single cloud to be seen. Clear skies are, 

 indeed, at some seasons, and in some places, often 

 more treacherous than cloudy ones : because, espe- 

 cially in places near the sea, or high mountains, 

 there are clouds of day and clouds of night, which 

 are regularly formed in the atmosphere, and again 

 dissolve there, even in the finest weather. When 

 the air is still, and the smokes ascend in tall col- 

 umns withoutblending much with the air, it is a sign of 

 rain, because it shows that the air near the earth is 

 in a state in which it will absorb or dissolve no more 

 moisture ; and it is the under stratum of the air that 

 keeps up the clouds ; so that when these are formed 

 and again absorbed, the absorption takes place at 

 their under sides, and not at their upper, just as the 

 snow showers that fall upon the hot and dry fields 

 in the spring melt below by the heat of the earth 

 sooner than above by the heat of the sun. Some- 

 times the smoke, when abundant, and when the air 

 does not evaporate the water, and allow the soot to 

 fall to the ground, forms a long flat stratum like a 

 thunder-cloud ; and that, like the thunder-cloud, 

 shows that there will be showers, or rain falling 

 from a considerable height, and therefore in large 

 drops. The reason is, that a portion of the lower 

 air resists the descent of the cloud, while the upper air 

 is parting rapidly with the moisture that it contains. 

 In these cases the evaporative, or drying power of the 

 lower air, is often wholly occupied in resisting the 

 descent of the cloud, so that the surface of the earth 

 in many places, and especially that of the green 

 P2 



