180 EXPLORATIONS ACROSS THE GREAT BASIN OF UTAH. 



tude from those which shall be determined, namely, that extremes of error are thus 

 avoided, although in single instances other methods may give better results. In cal- 

 culating the profile of a country, quite different rules must be followed from those best 

 answering for the computation of the altitude of a single mountain. 



The altitudes of points on the roads between Camp Floyd and Fort Bridger, Utah, 

 were computed before the yearly mean readings at Camp Floyd had been determined. 

 I had, therefore, to make use of the corresponding readings of the barometer at 

 both stations, which answers the same purpose, and of the mean temperature of the 

 days. But as the temperature, during the season of these surveys, was generally 

 moderate, and the difference of the altitude of the upper and lower stations mostly 

 not very considerable, the obtained values must be nearly correct. The altitude of 

 Fort Bridger, determined in that way, agrees perfectly with that obtained from a large 

 mean. Some of these observations could not be referred to simultaneous observations 

 at Camp Floyd or Fort Bridger, and I had to compare them with such obtained on 

 the same days at other camps, the altitudes of which had been determined before, or 

 even with camps of the preceding and following days. Although this method is very 

 objectionable as a general thing, I consider the results in this case as more reliable 

 because the circumstances were uncommonly favorable; and especially the corrections 

 for the daily variations of the barometer gave such complete compensation that the 

 plot of the barometric readings of the single stations could be filled up satisfactorily 

 for the intervening hours. Of the different values thus obtained for a point, the means 

 were taken, which probably give a close approximation to the real altitudes. 



ALTITUDE OF CAMP FLOYD. 



The determination of the mean reading of the barometer and thermometer at 

 Camp Floyd was a matter of considerable importance to me, because I wanted to 

 make use of them, and the altitude of the station computed from them, as a basis for 

 most of the other computations, as I have stated above. At our station observations 

 had been regularly taken during the 6 months from November, 1858, to April, 1859 ; 

 partly hourly, 16 a day; partly 6 every day, and partly at the hours of 7 a. m., 2 p. 

 m., and 9 p. m., every day. The mean of these was calculated with due reference to 

 the different number of observations, and the necessary corrections were applied. 

 This mean was found to be 25.129 inches at 32° of the mercury. The results of 

 observations during the next 6 months, from May to October, 1859, regularly taken 

 at the hospital at Camp Floyd, at the hours of 7 a. m., 2 p. m., and 9 p. m., were 

 kindly furnished by the medical department. Their mean, reduced to our standard 

 and station, is 25.150 inches. The mean for the whole year is, therefore, 25.140 inches, 

 English, at 32° of the mercury. 



The mean temperature of the year was deduced from 6 months' .observations at 

 our station ; 3 months' observations by Asst. Surg. Thomas H. Williams, medical 

 director of the Department of Utah, and 3 months' observations at the hospital, under 

 direction of Asst. Surg. J. Moore, U. S. A. It is 47° Fahrenheit. 



I assumed 30.050 inches as the mean reading of the barometer, the mercury re- 

 duced to 32° Fahrenheit, and 54° as mean air temperature at the level of the sea, best 



