METEOROLOGICAL EFFECTS OF DRAINING. 441 
as well as the refrigeration which attends all evaporation.* On 
the other hand, if the volume of water abstracted is great, its 
removal deprives its basin of an equalizing and moderating in- 
fluence; for large bodies of water take very slowly the tem- 
perature of the air in contact with their surface, and are 
almost constantly either sending off heat into the atmosphere 
or absorbing heat from it. Besides, as we have seen, lakes in 
elevated positions discharge more or less water by infiltration, 
and contribute it by the same process to other lakes, to springs, 
and to rivulets, at lower levels. Hence the draining of lakes, 
on a considerable scale, must modify both the humidity and 
the temperature of the atmosphere of the neighboring regions, 
and the permanent supply of ground-water for the lands lying 
below them. 
Meteorological Action of Marshes. 
The shallow water of marshes, indeed, performs this latter 
function, but, under ordinary circumstances, marshes exercise 
* The relative evaporating action of earth and water is a very complicated 
problem, and the results of observation on the subject are conflicting. 
Schiibler found that at Geneva the evaporation from bare loose earth, in the 
months of December, January, and February, was from two and a half to 
nearly six times as great as from a like surface of water in the other 
months, The evaporation from water was from about once and a half to six 
times as great as from earth. Taking the whole year together, the evapora- 
tion from the two surfaces was 199;°; limes from earth and 536;'; lines from 
water. Experiments by Van der Steer, at the Helder, in the years 1861 and 
1862, showed, for the former year, an evaporation of 602.9 millimetres from 
water, 1399.6 millimétres from ground covered with clover and other grasses ; 
in 1862, the evaporation from water was 584.5 millimétres, from grass- 
ground, 875.5.—WILHELM, Der Boden und das Wasser, p. 57; KREcCKE, 
Tet Ktimaat van Nedertand, ii., p. 111. 
On the other hand, the evaporation from the Nile in Egypt and Nubia is 
stated to be three times as great as that from an equal surface of the soil 
which borders it.—LOMBARDINI, Saggio Idrologico sul Nilo, Milano, 1864, 
and Appendiz. The relative thermometrical conditions of land and water in 
the same vicinity are constantly varying, and the hygrometrical state of both 
is equally unstable. Consequently there is no general formula to express the 
proportionate evaporation from fluid and solid geographical surfaces. 
