METEOROLOGY OF 1 897 
61 
AN ILLUSTRATION OF THE INFLUENCE OF IRRIGATION 
ON SOIL TEMPERATURE. 
§61. The control which irrigation gives of soil con- 
ditions is well known by students of irrigation and is more 
or less realized by farmers in the arid regions. The extent 
of this influence is, however, not often recognized, and it is 
rarely that an illustration as clear as was shown by the soil 
temperature observations during August, 1897, to be ob- 
tained. In this case our soil thermometers being placed in 
the grass plat were so situated, that the irrigation of the 
lawn flooded, to a depth of some inches, the ground where 
the instruments were placed, and the irrigation was con- 
tinued long enough to saturate the ground underneath. 
The temperature at a depth of six feet had been nearly uni- 
form at 62° for a number of weeks before the date of irriga- 
tion on August i2th. 
§62. With the application of the water it is noticed 
that the temperature immediately rises, reaching a temper- 
ature of 71° almost immediately after, d'he temperature 
fell almost immediately after the irrigation, so that during 
the next three days it had fallen to 64>^°. On August i6th 
the irrigation was repeated, and this time the effect of this 
added to the effect of the first was to increase the tempera- 
ture to 75 / 4 °. The temperature dropped rapidly to 69°, 
and then dropped gradually, not again reaching 62° until 
October, d'he effect of irrigation on the plat of ground and 
its vicinity, was felt for more than a month. 
§63. d'he effect on the temperature at two feet and at 
at three feet in depth was much the same. At the first irri' 
gation the temperature at two feet was increased over that 
at the lower depths. At the second irrigation the effect on 
the deep thermometer was almost as great as upon the two 
foot thermometer. 
For the depths less than two feet, the diurnal fluctuation 
is marked, and as the corresponding curves confuse the dia- 
gram, they are omitted. The shallower thermometers also 
show the cooling effect from evaporation so much that their 
temperatures fell below the deeper ones. 
§64. In view of the influence which temperature has 
upon the growth of plants, the importance of the fact shown 
in the diagram is api)arent. Evidently the irrigator can in- 
crease the temperature of the soil by application of water of 
proper temperature. It is also evident from corresponding 
observations at the shallower depths, that the cooling ef- 
ect on the soil from evaporation may be considerable. 
§65. But as tl.e application of water warmer than the 
