ATMOSPHERIC DISTURBANCES. 
57 
territory, the maximum amplitude of these tides, as measured by the barometer, is about one 
inch—corresponding to 1,000 feet of elevation; though in latitude 35° it is somewhat less. 
Hence the necessity for simultaneous observations at those points whose differences of altitude are 
to be determined by the barometer ; or, what is equivalent to it, corresponding observations at 
some fixed station, within the same barometric region, in order to mark the period and measure 
the amplitude of the oscillations for the determination of the correction due to them. 
The latter plan has been adopted in our reconnoissance. For its execution, we have been 
furnished by the Surgeon General’s Department whth unpublished records kept by officers of the 
medical corps at various military posts in the vicinity of our route, and use has been made also 
of corresponding observations upon Governor Stevens’ and Captain Beckwith’s lines of survey. 
On account of the slight knowledge heretofore existing with regard to the climatolog'cal 
character of the region between the Mississippi valley and the Pacific ocean, it could not be 
determined, in advance, between what limits the rnrial tides could be considered sufficiently 
coincident to render barometric observations, taken at different points, comparable. This ques¬ 
tion was elucidated by the construction of diagrams, which exhibit the curves of unequal pres¬ 
sure, observed upon our line, and the corresponding oscillations obtained from the various records 
previously referred to. The diagrams are appended to this report, and probably will be exam¬ 
ined with considerable interest. In noticing some of the ideas which they have suggested, it is 
not proposed to enter into a general discussion of the problem of variable atmospheric pressure : 
the data before us are too meagre. Until governments, or individuals, interested in scientific 
researches, choose to unite in an extensive system of atmospheric observations, we must continue 
to be dependent upon theories, more or less vague and unsatisfactory. Were America and 
Europe to combine in the undertaking, it would not be difficult nor expensive to arrange and 
carry out a plan of operations, whereby light-houses upon the coasts, and military posts in the 
interior, might be provided with instruments and observers ; and a comparison of the records 
thus obtained would lead to a solution of most of the laws of the so-called meteorological phe¬ 
nomena. This is one of the great desiderata of science at the present day. Our own govern¬ 
ment, by the co-operation of its officers of the army and navy, and by the voluntary contribu¬ 
tions of its citizens at home and abroad, might well take the initiative in the determination of 
the causes of winds, clouds, and rain ; of variations of heat and atmospheric pressure ; and thus 
add to the sum of human knowledge that which would be of incalculable value to man in every 
branch of practical industry. 
From a comparison of the observations appended to this report, it appears that in the Missis¬ 
sippi valley currents of moist heated air from the Gulf of Mexico create a disturbance of the 
atmosphere, and produce local storms. To what distance westward their effects are communi¬ 
cated to the barometer can scarcely be deduced from the limited data examined. Our observa¬ 
tions, however, at Napoleon, June 24, 1853, and those taken simultaneously at Memphis, 
marked a period of great atmospheric pressure. This same phenomenon was noted at all the 
barometric stations of the Mississippi valley, and at Fort-cribson in the Creek territory. 
The Llano Estacado and great western prairies, being heated by the sun’s rays, rarify the 
superincumbent atmosphere, modifying the climate, and doubtless also the series of barometric 
waves of the Mississippi valley; yet, from the diagram it appears that all the oscillations noticed 
at Fort Gibson, between July and September, inclusive, were felt almost simultaneously upon 
our line from Fort Smith to New Mexico. In October, the curves of variable pressure at Albu¬ 
querque still correspond to those observed at Fort Gibson, except as regards some of the periods 
of maxima and minima ; and in December, even as far westward as the Colorado Chiquito— 
Flax river—a striking similarity continues for a considerable period. 
The few observations collected for the month of December illustrate one important fact—the 
widely-spread influence of a single barometric wave. Between the 4th and 10th, a remarkably 
uniform rise and fall of the barometer is indicated at Fort Benton, near the eastern base of the 
Bocky mountains ; opposite, at St. Mary’s, on the head-waters of Clark’s Fork of the Colum- 
8 n 
