REPORT OF CAPTAIN HUMPHREYS TO THE SECRETARY OF WAR, 1855. 
13 
of many species, useful in au economical point of view, or interesting to science, have been 
determined. 
The precise range of the buffalo, the antelope, the prairie dog, the various species of deer, and 
of other animals, with that of numerous valuable trees and herbaceous plants, has been satis¬ 
factorily ascertained. Several forms of animal and vegetable life, noticed by earlier travellers, 
especially by Lewis and Clark, hut unknown since their time, have been re-discovered. 
The labors of the naturalists and the collectors attached to the several parties have resulted in 
a collection illustrating the natural resources of our country west of the Mississippi, more com¬ 
plete than will he found in all the museums of the United States and Europe combined. 
Lieutenant Williamson’s report shows a remarkable coincidence of the elevations deduced 
from barometrical observations with those obtained at the same time by the spirit level. The 
profiles of the Tejon pass and the Canada de las Uvas, delineated from the spirit level altitudes, 
differ so slightly from the barometrical profiles, that the barometer may be regarded as suffi¬ 
ciently accurate for the purpose of railroad reconnaissance in that climate. 
The report of Captain Whipple, topographical engineers, upon the manner in which the 
elevations for the elaborated profile of his route have been deduced, indicates moans by which 
great accuracy can be obtained in barometrical levelling over extensive regions, without the 
delay consequent upon the mode of eliminating those errors arising from irregular changes of 
atmospheric pressure, by simultaneous observations at near points. Between the Mississippi 
and the Pacific, these errors are in some instances equal to 1,000 feet. The investigation made 
by Captain Whipple leads to the following conclusions, regarding these irregular movements 
of the barometer : 
1st. They are of great magnitude, and if not taken into account may produce an error in 
the deduced altitude of many hundreds of feet. 
2d. They are hut slightly affected by local storms. 
3d. They may occur almost simultaneously over the whole interior portion of the continent. 
4th. They are actually identical within certain areas of great extent. 
These conclusions will he regarded with great interest by scientific explorers and those 
engaged in studying and observing meteorological phenomena. 
It has been suggested, in connexion with this, to make series of barometrical observations at 
military posts on lines crossing our territories from east to west, in order to determine the 
areas over which these irregular (abnormal) movements occur simultaneously. These having 
been ascertained, it will he merely necessary, in future explorations, to have corresponding 
observations made at one point in each of the barometrical areas, or regions, traversed by an 
expedition. The plan of observations proposed could be carried into effect at the cost of a few 
thousand dollars ; and, incidentally, would make important additions to meteorological 
knowledge. 
As a kindred subject, I beg leave to ask your attention to a proposed arrangement for im¬ 
proving the means of computing the observations for longitude of exploring parties. The best 
mode of determining longitudes by these parties, is that of observations upon moon culmi¬ 
nating stars. One night’s observations by a good observer will give a resulting longitude— 
the error of which will not exceed two miles, provided there are corresponding observations at 
some well determined point; but without these corresponding observations, errors, three or four 
times as great, may he introduced by the use of tables of the computed positions of the moon. 
Thus it appears that the field observations are more accurate than the means of computing used 
