RATE OF THE EVAPORATION OF WATER FROM THE TULARE LAKES. 195 
It will be observed that the evaporation ceased at night. The temperature of the air was 
always rapidly reduced after sunset, but there was no dew. As these low, night temperatures 
did not influence the result, we may take the mean of the day temperatures both for the air and 
the water at the time of observation, subject to the slight error caused by the deficiency of obser- 
vations on the 26th and 28th, and obtain approximately the temperature conditions of the air 
and water for that amount of evaporation. These results are, for the air 83°.9, for the water 
119.5; time, 46 hours. Height of barometer 29.30. 
Although at the time of these experiments I regarded the air as exceedingly dry, I have since 
been forced to the conclusion that its condition was not the most favorable to great and rapid 
absorption of water. The crests of the ranges of the Coast Mountains are not greatly elevated 
in that region, being, probably, less than four thousand feet, and during the day they are much 
heated by the sun ; they do not, therefore, cause the precipitation of all the moisture which the 
air brings with it from the sea, and its thorough desiccation is not accomplished. A great part 
of its moisture is necessarily retained, and a capacity for the absorption of more is given by the 
elevation of temperature which it suffers among the interior ranges and valleys of the coast, and 
finally upon the broad and heated plain. Tt is well to consider these conditions in connexion 
with the experimental results, and if the air is thus highly charged with moisture, the quantity 
taken up must be regarded as very large. At the rate of one-quarter of an inch a day, seven 
inches and a half in depth would be removed in thirty days, or seven feet, seven and a quarter 
inches in one year. According to Dr. G. Buist, the amount of evaporation from the surface of 
water at Aden, on the Indian Ocean, ‘‘is about eight feet for the year.’’! The basis of this state- 
ment is not given, but it is interesting to notice that the amount agrees with my experimental 
result. 
If we regard the experimental result as a fair measure of the evaporation from the lakes, we 
may readily calculate the amount of water taken from them during a month or year. We 
have 36 cubic inches of water for the daily evaporation from one square foot of surface, and 
consequently 522929.5 cubic feet from every square mile. This equals 16210.8 tons, or 
4,052,703 gallons—a quantity of which we can scarcely form an adequate conception, and yet 
it is for one day only. If we measure the amount of evaporation in depth, and assume that 
the quantity evaporated is equal during each month in the year, we have, as before observed, 
Seven feet seven inches and one-quarter for the yearly evaporation. The conditions which I 
have detailed do not, however, exist throughout the year. In the rainy months the evaporation 
is much reduced, or perhaps it almost ceases. It is almost certain, however, that the experi- 
ment does not show the full amount of evaporation for the summer ; it is undoubtedly much 
greater, and the results can only be regarded as approximate. They ar», however, important, 
and derive greater interest from the fact that few experiments of the kind have been made, and 
because the climatic conditions of that region are so peculiar.* 
Resemblance between the Tulare Valley and the Colorado Desert.—It will be seen, by comparing 
this description of the Tulare Valley with that given of the Colorado Desert, that the valleys re- 
semble each other in their important characteristics. It is probable that their geological history is 
Similar ; but, although of the same age geologically, the changes in the Desert Valley have 
been most rapid, and its complete dessication has long since been accomplished. This difference 
' Trans, Bombay Geographical Society, vol. ix, 1849-50, p. 39. TER" 
* The results of the experiment upon the amount of evaporation were communicated in a paper n dure rn 
Institute, at Washington, March 4, 1856, and subsequently published in the American Journal of Science, May, 1856. 
