442 TEE POPULAR SCIENCE MONTHLY 



center of a storm rises to great heights where, in middle latitudes, it 

 gets into the swiftly eastward moving layers that carry it and its ice 

 particles far ahead of the rains. There are other ways by which such 

 clouds can be formed, but that just explained is one of the most com- 

 mon, and as, in this case, they are only the overrunning portion of a 

 storm that is coming on in the same general direction, the proverb just 

 quoted evidently is well founded. 



When the air is rather damp and the day is warm great cumulus or 

 thunderhead clouds are apt to form, as a result of strong convection, 

 and produce frequent local showers. Hence the following proverb : 



"When clouds appear like rocks and towers, 

 The earth's refreshed by frequent showers." 



Another interesting phenomenon, familiar to all who live among 

 the mountains, is the formation of a cloud along the highest ridges, 

 due, of course, to the upward deflection of the wind as it blows against 

 their sloping sides. This mechanical, or forced, convection produces 

 the usual cooling, which, when the air is damp, results in the forma- 

 tion of cloud. Hence the truth of the proverb that tells u& : 



"When the clouds are upon the hills, 

 They'll come down by the mills." 



Sound 



"There is a sound of abundance of rain." 



— Elijah. 



When the air is full of moisture its temperature tends rapidly to 

 become equalized — the colder places are warmed by condensation and 

 the warmer cooled by evaporation. In this way the atmosphere is 

 freed from the innumerable temperature irregularities that prevail 

 during dry weather, irregularities that, as Tyndal showed many years 

 ago, strongly reflect and dissipate sound. We see, then, that when the 

 air is homogeneous, which it is far more likely to be when damp, it will 

 convey sound much better than it will when filled with inequalities, and 

 hence there is good reason to accept the proverb, and other similar ones, 

 that says : 



"Sound traveling far and wide 

 A stormy day will betide." 



Not only the hearing, but the seeing as well, is improved by the 

 homogeneity of the atmosphere, and this, too, has its appropriate prov- 

 erbs of which the following is a good example: 



"The farther the sight, the nearer the r&in." 



