REPORT OP CAPTAIN HUMPHREYS TO THE SECRETARY OF WAR, 1855. 13 



of many species, useful in an economical point of view, or interesting to science, have beep 

 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, but 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 be 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 bo 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 means 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 but 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 be 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 be 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 be 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 



