60 
RESULTS OF THE COMPUTATION. 
an oversight, due to the hasty manner in which the reductions were made, were not brought to 
that standard ; but, in the first computations, the corrections for that element were based upon 
the observed reading, without regard to the hour of observation. Mr. Blodget soon saw that 
the effect was to introduce an error into the results, and therefore he assumed a table of modifi¬ 
cations, by which each of the high temperatures was reduced, and the low temperatures were 
increased, by a quantity depending upon the observed reading. This was a wise precaution, 
serving to diminish the inaccuracies that were introduced into the first results, and leaving but 
small residual errors. The necessity of reducing the temperatures to their mean determinations 
was not understood until too late to apply the rule to the computations. It is believed, however, 
that the errors resulting from this neglect will not be found of much magnitude, and they are 
probably all upon the safe side, viz : they have increased the elevations of those points where 
observations were made during the middle portion of the day ; rendering the grades too abrupt 
and the profile too broken to represent the natural slope of the ground. 
In concluding the remarks with regard to this subject, it may not be deemed improper to 
mention that our operations have excited a spirit of inquiry after facts, and an inves¬ 
tigation of the laws that govern the fluctuations of the barometric column. Parties that 
have succeeded ours in the field have thus been enabled to profit by our experience, and obtain 
results which prove that the general method of determining differences of altitude by measure¬ 
ments of atmospheric pressure is susceptible of a closer degree of accuracy than its advocates 
have heretofore claimed. The importance of such a determination will be appreciated by those 
who reflect upon the vast expense and labor which would be required to obtain profiles of the 
interior portion of our territory by any other process. Excepting the small errors that have 
been referred to, this portion of our work is believed to possess a satisfactory degree of accuracy. 
Each camp having been referred directly to the sea-level, the minor discrepancies, which in such 
a reconnoissance cannot easily be avoided, have not been suffered to accumulate. The camps, 
therefore, may be considered as the standard points of reference for the profile line. The con¬ 
tour of the ground between them was determined by an independent system ; aneroid or mer¬ 
curial barometers having been observed at the most important stations upon each day’s march, 
and topographical sketches made of the whole belt of country within the field of view. The 
data thus gathered forms material for a series of maps upon a scale of to-otto with curved lines, 
fine and coarse, to represent the sections of horizontal planes, ten and fifty feet apart. Although 
founded upon rapid examinations—strict accuracy not being claimed for all of the details—a 
delineation upon this scale was necessary, in order to exhibit the character of the country in 
accordance with our field-notes. Upon the topography of these maps we may trace the line 
most favorable for a railroad, and measure the curves and grades which the contour would- 
require. A profile of this route has also been made upon the same large scale, showing approx¬ 
imately the cutting and filling necessary to produce the grades which are given. This differs 
materially, both as regards length and elevation, from the one previously submitted to the 
department, the latter exhibiting merely the wagon trail with the altitudes uncorrected for 
abnormal error. 
In order to avoid the great expense of publishing the detailed maps and profiles previously 
alluded to, the greater part of the results which they have enabled us to arrive at, relating to 
distances and grades, as well as excavation and embankment, is condensed; and the former is 
presented in the accompanying table, marked Appendix N. In that may be found one of 
the most serious objections to which this route is liable, viz: a long succession of heavy grades 
through the mountainous regions of the interior. Future examinations over sections already 
referred to in the preceding pages, or through passes not yet discovered, will undoubtedly 
enable the engineer to modify and greatly improve the location of the line. The steep declivity 
and expensive rock-cutting in the San Antonio canon, may be rendered unnecessary by following 
the Galisteo river. The elevated and somewhat broken region, between San Francisco Springs 
and Aztec Pass, may probably be avoided by pursuing a more southerly course, as indicated by 
