CHAPTER IX. 
Discussion of Barometric Observations, and Tables of Altitudes and Distances, of the line 
explored from Westport, Mo., to Great Salt Lake City, Utah Territory ; also Tables of 
Simultaneous Observations in, and Data for Profiles of, the mountain passes of the line. 
1853. 
I.—Introduction to, and corrections applied in, barometric computations.—Table for horary corrections of observations.— 
Corrections for extreme air temperatures.—Comparison of field barometers with Dr. Engelmann’s barometer at St. 
Louis, Missouri, both before and subsequent to the surveys.—Table of monthly mean observations at St. Louis, by Dr. 
Engelmann. 
II.—Barometric and meteorological observations, and table of altitudes and distances, for the profile of the line of survey from 
Westport to Great Salt Lake City. 
HI.—Data for profile of Roubideau’s Pass. 
IV.—Simultaneous meteorological observations at Coochetopa Pass. 
V.—Observations for a tunnel or deep cut in the Coochetopa Pass, allowing fifty yards as the width of the ridge at top. 
IV.—Table IV resumed. 
VI.—Data for the profile of the Coochetopa Pass, and declivities near its summit. 
VII.—Simultaneous meteorological observations at the pass and on the route followed across the Wahsatch range. 
VIII.—Data for the profile of the route followed across the Wahsatch mountains. 
I .—Introduction to, and corrections applied in, barometric computations .— Table for horary corrections 
of observations.—Corrections for extreme air temperatures .— Comparison of field barometers with Dr. 
Engelmann's barometer at St. Louis, Mo., both before and subsequent to the surveys .— Table of monthly 
mean observations at St. Louis, by Dr. Engelmann. 
The Bunten barometers (Nos. 496 and 551) are exclusively relied upon for the determinatio 
of altitudes of the entire line. The readings of the aneroid barometers exhibit variable errors; 
and as the mercurial barometers retain their reliable and uniform character throughout, no neces¬ 
sity exists for the use of the aneroids, the records of which are, therefore, not given. 
The zero errors found by Doctor Engelmann, in his comparison at St. Louis, to apply to the 
Bunten barometers before the commencement of the work, did not remain as between the two 
instruments, even at the first considerable camps of the survey. They were, therefore, rejected 
in all the computations, and no zero error was at any time applied. For mean readings the 
two barometers ^usually agreed very nearly—the difference between them being that No. 496 
was too slow in its movement when considerable changes of altitude occurred, and required 
correction or the substitution of the other in such cases. 
For mean readings at stations where several observations were taken, the results of both are 
believed to be a very near approximation to standard accuracy, and the instruments appear 
to have been but slightly deranged at the termination of the survey. The zero errors found in 
them by Doctor Engelmann, on their return, were obviously introduced after the close of the 
work, and do not require to be applied to it. 
In the discussion of the observations, the readings were first corrected for temperature to the 
height of the mercurial column at 32° Fahrenheit. A minor error of non-adaptation of the 
common formula, to the temperature expansion determined by Shumacher for barometers ot 
this construction, is thus avoided, and the greater advantage gained of combining all the obser¬ 
vations at a station in a correct mean reading, to be used in a single computation of the altitude* 
12 g 
