IMPORTANCE OF SUMMER RAINS. 213 



form, during the season in which the atmosphere fm*nishes a 

 slender supply of the beneficent fluid so indispensable to vegetable 

 and animal life.* 



Irriportance of Summer Rains. 



Babinet quotes a French proverb : " Summer rain wets nothing," 

 and exj^lains it by saying that at that season the rain-water is 

 "almost entu'ely carried off by evaporation." "The rains of 

 summer," he adds, " however abundant they may be, do not pene- 

 trate the soil beyond the depth of six or eight inches. In sum- 

 mer the evaporating power of the heat is five or six times greater 

 than in winter, and this force is exerted by an atmosphere capable 

 of containing five or six times as much vapor as in winter." " A 

 stratum of snow which prevents evaporation [from the ground], 

 causes almost aU the water that composes it to filter into the 

 earth, and forms a provision for fountains, weUs and streams 

 which could not be furnished by any quantity whatever of sum- 

 mer rain. This latter, useful to vegetation like the dew, neither 

 penetrates the soil nor accumulates a store to supply the springs 

 and to be given out again, into the open air." f 



* The accumulation of enow and ice upon the Alps and other mountains — 

 which often fills up valleys to the height of hundreds of feet — is due not only 

 to the fall of congealed and crystallized vapor in the form of snow, to the con- 

 densation of atmospheric vapor on the surface of snow-fields and glaciers, and 

 to a temperature which prevents the rapid melting of snow, but also to the 

 well-known fact that, at least up to the height of 10,000 feet, rain and snow are 

 more abundant on the mountains than at lower levels. 



But another reason may be suggested for the increase of atmospheric hu- 

 midity, and consequently of the precipitation of aqueous vapor on mountaia 

 chains. In discussing the influence of mountains on precipitation, meteorolo- 

 gists have generally treated the popular belief, that mountains "attract" to 

 them clouds floating within a certain distance from them, as an ignorant preju- 

 dice, and they ascribe the appearance of clouds about high peaks solely to the 

 condensation of the humidity of the air carried by atmospheric currents up the 

 slopes of the mountain to a colder temperature. But if mountains do not 

 really draw clouds and invisible vapors to them, they are an exception to the 

 universal law of attraction. The attraction of the small Mount Shehallien was 

 found sufficient to deflect from the perpendicular, by a measurable quantity, a 

 plummet weighing but a few ounces. Why, then, should not greater masses 

 attract to them volumes of vapor weighing many tons, and floating freely in 

 the atmosphere within moderate distances of the mountains ? 



f Mudes et Lectures, vol. vi., p. 118. The experiments of Johnstrup in tht 



