W. P. Blake on Evaporation on the Tulare Lakes. 365 
Arr. XX XVIII.—On the rate of Evaporation on the Tulare 
Lakes of California ; By Wm. P. Buaxe, Washington, D. C. 
Read before the National Institute, Washington, D. C., March 4th, 1856. 
Tse Tulare plains of California wear a most desert-like and 
barren aspect during the summer and autumn. ‘Treeless and 
without green vegetation, the surface becomes parched by the 
rays of an unclouded sun, and gives unobstructed passage to 
steady currents of air which pass inland from the ocean towards 
the Sierra Nevada. ‘These winds, after passing the ranges of the 
Coast Mountains and becoming partially desiccated in their tran- 
sit, impinge upon and traverse the plain, and reach the foot-hills 
f its eastern margin with a high temperature and apparently 
little moisture. 
In the month of August, 1853, while with the U. S. Pacific 
R. R. survey, commanded by Lieut. R. 8. Williamson, we en- 
camped on the banks of Ocoya Creek, among the foot-hills of 
the Sierra, and every day felt the hot wind blowing inland to- 
ward the mountains. T'he parching effect produced by these 
winds, and the fact that after leaving the Coast Mountains they 
Sweep over the broad and shallow Tulare lakes, induced me to 
desire to ascertain the rapidity of evaporation of water when 
fairly exposed to their action, and if possible to arrive at an ap- 
proximate estimate of the amount of water removed daily from 
these lakes. For this purpose, I made the experiment of expos- 
ing water in a pan to the action of the wind, and noting the 
amonnt removed each day. 
The valley of Ocoya Creek, in which our camp was located, 
has been formed by the erosion of the creek in a plateau of soft 
tertiary strata. It is thus bounded on each side by hills of hori- 
zontal stratification, and these were from 300 to 900 feet in 
ight. They were perfectly barren and parched, and the only 
Breen vegetation visible was confined to the immediate banks of 
the creek. The altitude of the camp was 738 feet above mean- 
tide, and its distance from the open plain of the Tulares, two 
miles, from the lakes 25 miles, and from the sea in a direct east 
and west line 120 miles. The width of the valley was about 
ove quarter of a mile, and its direction was nearly east and west, 
So that the breeze from the plain followed its course without de- 
ton, 
The wind usually blew gently from the mountains during the 
night and early in the moruing, but after the sun had risen, and 
about 10 o’clock its direction was reversed and it blew steadily 
and often strongly from the west or northwest until sunset, when 
it generally ceased. 
