APPENDIX K. 
TABLES OF INSTRUMENTAL ERRORS AND HORARY CORRECTIONS 
to be applied to the Barometric Observations; with Climatological Remarks, and Chart. 
PREPARED BY Mr. LORIN BLODGET. 
[Norr.— This appendix exhibits the plan pursued in the first reduction of the barometric observations, when it was 
necessary to present, without delay, a profile to accompany the preliminary report. Since then, this subject has under- 
gone revision ; and the system followed by Mr. Blodget has been replaced by another, which will be found described in the 
topographical report. The elements for horary variation remain unchanged.] 
Determination of elements for the reduction of barometric observations for heights.— Remarks upon 
the value of the observations.—Curves of daily oscillation of barometric column in New Mexico.— 
Report and chart of climatological investigations. 
The direction given to the barometric reductions of the survey, (made by Lieutenant Whipple, 
topographical engineers, for a railroad route near the 35th parallel,) differs somewhat from that 
usual to these observations, and the following notes and explanations of the processes may be 
necessary. The large number of barometric observations made, and the general accuracy and 
uniform comparison retained throughout the survey, by the instruments employed, render the 
observations of this extended line unusually important and valuable. Determinations made by 
them are almost the best possible by this mode of survey, and for this reason | great care was 
required, and was given, to their reduction.* 
The first series of observations made with the barometers at Cincinnati, Little Rock, and Fort 
Smith, were employed to determine positive comparisons of the instruments among themselves, 
those given by the maker not being found correct after transportation. The best results that 
could then be determined for zero error were obtained from these, and from comparisons with 
other barometers. The relative position of the instruments, as thus determined, was found to 
be the same at Albuquerque and atthe termination of the survey ; and the slight zero error 
possibly remaining, in the absence of opportunity to compare anew with an absolute standard, 
would be unimportant. 
The observations at Cincinnati, Napoleon, Little Rock, and Fort Smith, are given in full, to 
show the comparison of the instruments. The column headed di Yferente, gives the measure of 
variations of each instrument from the cistern barometer, No. 790. By full comparison, this 
last was considered too low by .019 of an inch, and the differences here given should be diminished 
by this quantity, to be regarded as comparisons with the standard ultimately assumed. The 
original comparisons of the maker, and the corrections as finally determined and applied, follow : 
9 The barometric observations of the Pacific railroad route near the 35th parallel, under the direction of Lieutenant 
Whipple, were reduced in a manner somewhat different from the usual course, and the following notes and explanations 
of the processes may be nec^ssary. The number of these observations was unusually great at each of the camps and im- 
portant points, and the instruments proved to be of the best character, and to have retained a uniform comparison among 
themselves throughout. Determinations from so large a number of good observations are almost the best possible in 
barometric survey, and for this reason great care was given to their reduction. 
