176 EXPLORATIONS ACROSS THE GREAT BASIN OF UTAH. 



time nearer to San Francisco, I preferred to base the corrections throughout on Camp 

 Floyd, because the climate of San Francisco is one of periodical changes, while that 

 of the interior is non-periodic, and because San Francisco is several thousand feet lower 

 than the Basin. The difference of the monthly mean readings of the barometer from 

 the yearly mean has not been found analogous in both districts, although many of the 

 great variations of the atmospheric pressure will undoubtedly be felt simultaneously in 

 the interior of Utah and on the Pacific coast. 



The diagram of the observations at ( 'amp Floyd, corrected for the horary oscilla- 

 tions, showed in general a satisfactory agreement with the corresponding diagrams of 

 the single camps, and even for the most western point reached by us ; for as regards 

 the city of Genoa, in Carson Valley, Utah, these diagrams agree better with each other 

 than those for Genoa and San Francisco. Local storms and rains in the single mount- 

 ain ranges affect the parallelism of the diagrams in some instances ; but the differences 

 produced in that way are probably not considerable, and partly, at least, are counter- 

 balanced bv the corresponding changes in temperature, &c* 



Between the abnormal variations of the barometers at Camp Floyd and Fort 

 Bridger I also found a most remarkable coincidence, and nearly simultaneous changes, 

 when I plotted the diagrams of corresponding observations, made very carefully at 

 these points in September and October, 1858. 



CORRECTION OF THE OBSERVED AIR-TEMPERATURES. 



The method of computation requires the introduction of the mean temperatures 

 of the days, instead of the observed temperatures. To find the mean temperature more 

 accurately, and make the correction more systematic, I have deduced the following 

 tables from observations made in connection with the hourly observations of the ba- 

 rometer for determining the horary oscillations of the mercurial column. These inter- 

 esting tables show the mean difference of the temperature of each hour from the mean 

 temperature of the day for different stations and seasons. The curves on plate B repre- 

 sent these variations graphically. The marks * indicate the times of sunrise and sun- 

 set. 



As no observations had been made during the hours of night, the mean tempera- 

 ture of the twentv-tbur la airs was calculat< d under the supposition that the temperature 

 decreases regularly from b p. m. to near sunrise, which, in the highly elevated re- 



* Long aft.r the c« inputati. n , t the altitudes tad been finished, ] 



[ took up the study of the hygrometrical obser 





f this report. They impressed me still more 





ctually presents the same climatical features as 





that when the local storms occur, the hygro 









; although I still repudiate the introduction of 



the force of vapor into tin is;- nu ih fun ula-. Ii\ them he is also em 





tables of horary ( - ted to the single observations. 





