182 EXPLORATIONS ACROSS THE GREAT BASIN OF UTAH. 



The heaviest precipitation of rain takes place during the fall and winter, but gen- 

 erally every month has some rain, and the climate of Utah does in that respect by no 

 means exhibit the periodicity of the climate of California, and of more southern lati- 

 tudes. 



During the summer months the showers seldom continued any length of time?, 

 and frequently only a few drops fell. The precipitation i s m0 st copious near high 

 mountains, not only for the same causes which in all countries favor the precipitation 

 of moisture on high mountains, but also, it appears, because the clouds and drops of 

 rain, while sinking through the parched lower strata of the atmosphere, are partly again 

 dissolved into vapor, and thus become less before reaching the bottom of the valleys, 

 unless the rain should happen to be heavy. This is the contrary of what takes place 

 in moister climates, where the quantity of rain frequently increases with every foot of 

 its descent through the air, which is saturated with moisture. 



In June we had no rain in the field, but in July numerous short showers occurred, 

 which, in the aggregate, amounted, however, only to 2 inches of rain. At Camp Floyd 

 2.28 inches were measured in July. I am unableto determine whether the difference in 

 the amount of precipitation between Camp Floyd and Salt Lake City, as exhibited by 

 the above table, is mainly due to the irregularity of the distribution of rain and snow 

 in the different years, or to other causes, although I have no doubt but that the fall of 

 rain and snow is more abundant at Salt Lake City, which is situated at the very foot 

 of the high and wide range of the Wahsatch Mountains, near the most elevated sum- 

 mits of which considerable banks of snow remain unmelted all the year round, although 

 they cannot be said to reach the limit of perpetual snow, and the moister atmosphere 

 of which is indicated by a different vegetation than farther off these mountains near 

 Camp Floyd, and in the other open valleys. In 1857, six feet of snow fell near Salt 

 Lake City; certainly much more than is likely ever to fall at Camp Floyd during a 

 single winter. 



Dew falls very rarely in the vast desert valleys and on most of the mountain 

 ranges of Western Utah, in the so-called Great Basin. The scarcity of grass in the 

 valleys, which are mostly covered with a thin growth of Artemisia and other desert 

 plants, combined with the great dryness of the atmosphere, which is indicated by the 

 small amount of rain, is not favorable to its formation. On our whole. march from 

 Camp Floyd to the Sierra Nevada and back, during May, June, July, and part of 

 August, that is, from the time when it was still snowing occasionally to the time when 

 the greatest heat of the summer was over, we observed dew only on three mornings, 

 and then it was confined to a border of grass of only a few feet in width along the banks 

 of creeks. In Section V of the Geological Report, I have shown that the cause of this 

 great deficiency of moisture is a consequence of the geographical situation and hypso- 

 graphical character of the country. 



The remarkable dryness of the atmosphere influences also its electric condition. 

 We know that dry air is a non-conductor of electricity, while moist air is a conductor. 

 The electricity which is constantly developed in various ways, is, under ordinary cir- 

 cumstances, mostly at once conducted to the earth or diffused in the moist air. In the 

 comparatively moist climate of Western Europe, in Germain", for example, electricity 



