xxii 
BOTANY. 
The degree of dryness of the air is also shown by the results of a series 
of careful measurements of the actual amount of eYaporation taking place in 
vessels of water exposed to the full hifluence of sun and wind. The portion 
of these measurements made during fifteen days in June, fifteen days in July, 
and fourteen days in August, 1868, give very closely approximating means, 
and a general average daily evaporation of .5107 inches. Of this amount 
.4019 inches, or very nearly four-fifths, were evaporated between 6.00 a. m. 
and 6.00 p. m. The maximum evaporation for any hour observed was .0607 
inches, and the largest amount recorded during any six hours is .3333 inches 
between 10 a. m. and 4 p. m., as shown in the following readings for July 23d, 
at Camp Ruby. 
Record of Evaporator ; Camp Ruby, July 23, 1868. 
read- 
.pora- 
Thermometer. 
Hour. 
Evaporator 
ing. 
Amount eva 
ted. 
Dry bulb. 
Wet bulb. 
Difference. 
Black bulb. 
Clouds. 
Wind. 
Notes. 
In. 
In. 
°F. 
°F. 
°F. 
°F, 
6.20 a. m. 
.2690 
65-4 
59-3 
6.1 
Clear. 
East, light. 
8.03 
.2963 
.0273 
77.0 
61 .2 
15-8 
146.6 
Clear. 
East, light. 
9.00 
• 3203 
.0240 
80.4 
61.7 
18.7 
155-2 
Clear. 
East, light. 
10.00 
.3604 
.0401 
82.0 
58.9 
23.1 
165.2 
Clear. 
North, light. 
11.00 
.4182 
.4746 
.0578 
.0564 
85.3 
85.6 
5S-2 
30.1 
167.0 
Clear. 
Clear. 
North, light. 
East, moderate. 
X2.00 m. 
SS.6 
30.0 
167.0 
1. 00 p. m. 
.5326 
.0580 
87.0 
55-3 
31.7 
168.8 
Clear. 
East, fresh. 
2.00 
.5876 
.0550 
84.8 
54-6 
30.2 
169.0 
Clear. 
Northeast, light. 
3.00 
;6426 
•0550 
84.2 
5S-0 
29.2 
IS5-0 
Clear. 
Northeast, moderate. 
Maximum, 89.2°. 
4.00 
•6937 
• 051 1 
82.8 
54-7 
28.1 
156.2 
Clear. 
Northeast, light. 
S'OO 
•7257 
.0320 
81.7 
55-8 
25-9 
146.0 
Clear. 
East, light. 
6.00 
.7440 
.0183 
78.0 
76.4 
52-4 
25.6 
Clear. 
West, fresh. 
7-03 
.7644 
.0204 
Clear. 
North, moderate. 
8.18 
•7915 
.0271 
.0106 
75-0 
6g.o 
69.3 
67.6 
67.2 
Clear. 
West, fresh. 
West, light. 
West, light. 
West, light. 
East, very light. 
9.00 
.8021 
51. s 
5I-0 
So-4 
58.3 
17.2 
Clear. 
10.03 
• 8183 
.0162 
18.3 
17.2 
8.9 
Clear. 
11 .00 
.8327 
.0144 
.0496 
Clear. 
6.3s a. m. 
.8823 
Clear. 
Minimum, 45.4°. 
General Character of the Vegetation. The following statements 
are based upon the results of field-work in Nevada in 1867 and 1868 and in 
Utah in 18f)0. Entering Nevada from Cahfornia, collection was commenced 
on the 16th of July, 1867, in the valley of the Truckee River by Mr. W. W. 
Bailey, botanist of the expedition, and was continued through the season but 
confined wholly to the district between the Virginia and Pah-Ute Mountains. 
The summer was already so far advanced that the earlier vegetation had dis- 
