916 IMPORTANCE OF SUMMER RAINS. 
water is “almost entirely carried off by evaporation.” “The 
rains of summer,” he adds, “however abundant they may be, 
do not penetrate the soil beyond the depth of six or eight 
inches. In summer 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 all the water 
that composes it to filter into the earth, and forms a provision 
for fountains, wells, and streams which could not be furnished 
by any quantity whatever of summer 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.” * 
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 mountain 
chains. In discussing the influence of mountains on precipitation, meteorologists 
have generally treated the popular belief, that mountains “ attract” to them 
clouds floating within a certain distance from them, as an ignorant prejudice, 
and they ascribe the appearance of clouds about high peaks solely to the cou- 
densation 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 ? 
* Etudes et Lectures, vol. vi., p. 118. The experiments of Johnstrup in 
the vicinity of Copenhagen, where the mean annual precipitation is 234 
inches, and where the evaporation must be less than in the warmer and drier 
atmosphere of France, form the most careful series of observations on this 
subject which I have met with. Johnstrup found that at the depth of a 
metre and a half (59 inches) the effects of rain and evaporation were almost 
imperceptible, and became completely so at a depth of from two to three 
metres (64 to 10 feet). During the summer half of the year the evaporation 
rather exceeded the rainfall ; during the winter half the entire precipitation 
was absorbed by the soil and transmitted to lower strata by infiltration, The 
