Page:Popular Science Monthly Volume 78.djvu/452

442 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 common, 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 formation of cloud. Hence the truth of the proverb that tells us:

 When the clouds are upon the hills, They'll come down by the mills."

 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 TyndalTyndall [sic] 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 proverbs of which the following is a good example: