194 
GEOLOGY. 
perature of the water, which is fully exposed in the shallow lakes to the rays of an unclouded 
sun, and becomes much heated. 
The parching effect produced by these winds, and the evident rapidity of evaporation of any 
water exposed to their action, induced me to make an experiment to determine, if possible, the 
amount of water taken up each day. This experiment was made at the depot camp, on Ocoya 
Creek, in the following manner: A large sheet-iron pan, such as is used by the miners for 
“prospecting,” and which corresponds very nearly in size and shape with an ordinary milk-pan, 
was placed upon a firm stand about two feet above the surface of the ground. This pan was 
nearly filled with water and a thermometer and small ivory scale were immersed in it. The 
whole was in a situation favorably exposed to the action of the winds, and was protected from 
the direct rays of the sun by a shed, covered with brush and leaves. The shade prevented the 
sun from unduly heating the water by acting on the bottom and sides of the pan. The amount 
of evaporation was noted from time to time by the height of the water on the scale. The results 
are given in the annexed table. 
TABLE SHOWING THE AMOUNT OF DAILY EVAPORATION AT OCOYA CREEK, CALIFORNIA. 
Date. 
Time. 
Ther. 
air. 
Ther. 
water. 
Quantity 
evaporated. 
Daily 
evaporation. 
Kemarks—winds, &c. 
1853. 
Inches. 
August 26 
Sunrise_ 
650 
62° 
12 m. 
2 p. m- 
100° 
80° 
fa 
6 d. m_ 
78° 
fa 
l 4 ff 
Wind NW. and Steady from 11 a. m. till sunset. 
“ 27 
r‘ 
Sunrise- 
600 
580 
9 a. m_ 
85° 
70° 
fa 
Wind rising, and from the SW. 
12 m. 
96° 
78° 
2 p. m_ 
100° 
820 
fa 
Wind strong, and from NW. 
4 p. m_ 
100° 
80° 
fa 
5. 30 p. m.. 
96° 
78° 
fa 
fa 
“ 28 
6 a. m_ 
60° 
56° . 
12. 30. 
95° 
78° 
fa 
Wind strong since 11 a. m. 
4. 30 p. m.. 
fa 
6 p. m_ 
fa 
4 
Wind ceased at 6. 
“ 29 
6 a. m_ 
52° 
60° 
1 b 
12. 30 p. m.. 
86° 
74° 
fa 
Wind rising at 9 a. m. 
4 p. m_ 
900 
750 
fa 
fa 
From this table it will he seen that the observations were continued for four days, and that 
the mean daily evaporation was one-quarter of an inch. This was shown not only by the sum 
of the daily or hourly results, hut by the total loss in the four days as indicated on the scale at 
the close of the experiment. This result was below my anticipations, and yet when the depth 
of evaporation is multiplied by the superficial area, the quantity appears enormous. The 
rapidity of the evaporation was doubtless retarded by impurities in the water, which was taken 
from the creek, and soon deposited a slight sediment, and on the third day was covered with a 
thin film or pellicle, probably of light dust, which must have greatly protected the water from 
the action of the air. 
