202 EXPLORATIONS ACROSS THE GREAT BASIN OF UTAH. 



uration before it has carried off the surplus moisture of the air from that point; there- 

 fore the common saying that a wind is too cold to bring on rain. The average amount 

 of vapor in 1 cubic foot of air at Camp Floyd, in September, was 1.16 grains, and the 

 amplitude 1.44 grains. 



At Camp Floyd, in August, the conditions were similar. The maximum took 

 place from 8 to 9 a. m; then followed a gradual decrease till 6 a.m., when the humid- 

 ity increased again steadily, as in Woodruff Valley, to the time of the maximum at 9 

 a. m. Only a slight check was felt at the time of sunrise, but no perceptible depres- 

 sion. The average quantity was 2.59 grains, the amplitude 1.72 grains— more than I 

 have observed at any other point. 



At Camp Floyd, in April, the whole conditions were different, as I have stated 

 before, in connection with Table C; and, therefore, the variations were also entirely 

 different. There was a sunrise minimum at 5 a. m, a maximum at 10 a. m., a mini- 

 mum at 7 p. m., as low as the first one, and a second but lower maximum at 11 p. m. 

 These variations are unlike those at Philadelphia, but similar to those observed in 

 Western Europe. The average amount of vapor was 1.68 grains, the amplitude only 

 0.49 grains. 



The oscillations at Fort Kearney in June were somewhat similar, but the average 

 amount of moisture there was 6.75 grains, much more than I have observed in any 

 month in Utah, and even more than at Philadelphia in June, with, however, a lower 

 mean temperature, and, consequently, more complete saturation at the latter place. 

 The amplitude amounted to 1.10, while at Philadelphia only to 0.65 grains. 



The oscillations at Fort Laramie in the first days of August were not so charac- 

 teristic, but more influenced by contending agencies. Those at Genoa in June are, 

 of course, more similar to the other from Utah, but they exhibit some peculiarities. 

 The maximum took place at 9 a. m., but the minimum as early as 1 p. m., when the 

 same causes mentioned in connection with the relative humidity and the declining 

 temperature caused an increase of the quantity of vapor, which culminated at 4 p. m. 

 The rapid decrease of temperature caused a second minimum at 8 p. m., not quite as 

 low as the first one. The upward currents of air had then subsided, while the evapor- 

 ation continued in the damp valley. The humidity, therefore, increased again, suffered 

 a slight check shortly after sunrise, the same as at Woodruff Valley, when, as there, 

 it soon continued increasing to the maximum. The mean amount was 2.67 grains, the 

 difference between the largest and smallest quantity 1.62 grains. 



The hourly variations of the force of vapor and its absolute quantity are not less 

 abnormal in the region covered by our explorations; but, as they depend upon the 

 weight of vapor and the degree of temperature, and indirectly upon the relative 

 humidity, and are determined by their relative quantity and changes, I may be shorter 

 in my remarks. 



Table F shows that at Philadelphia one minimum and one maximum takes place 

 every day, the former about the time of sunrise, when the temperature is lowest and 

 the quantity of vapor smallest, the latter in the afternoon, when the temperature is 

 highest and the quantity of vapor largest, while the relative humidity is not too low. 

 In January the minimum takes place between 6 and 8 a. m., and the maximum lasts, 



