METEOROLOGY OF THE FIELD EXPLORED. 
129 
ever elevation; and none of the elevations are such as to give extreme temperatures, or to break 
the force of the general modifying influences here referred to. 
With but few fesults of recent observation in the shape of mean temperatures, or measures 
of amount of rain and snow, a few statements comprising such stations as have been observed 
are given in a tabular form. Their general significance may here be mentioned. In the first, 
the mean temperatures for the last five years are given at the stations most nearly in a line from 
Fort Snelling westward. In this series Fort Clark and Fort Union, of the Missouri, are given 
as observed at an earlier date, as no recent observations are at hand from these posts, and they 
are much needed to fill up the line. The observations at Fort Benton of December, and 
those of the St. Mary’s valley of January and February, are combined; the remaining obser¬ 
vations, though made and their general character known, not being at hand. 
It wifi be seen that the mean temperatures increase rapidly westward for all parts of the year, 
except the summer months, though the latitude constantly increases, and the elevation also, 
except at the immediate coast of the Pacific. Thus, for the winter months, five years’ observa¬ 
tions at Fort Snelling, one year at Fort Clark, (two months’ observations,) one winter at Fort 
Union, one winter at Fort Benton and St. Mary’s, three winters at Lapwai on the Kooskooskia 
river, we have— 
Fort Snelling, latitude 45°.temperature 13° 3 
Fort Clark, latitude 47°. “ 14°.5 
Fort Union, latitude 48°. “ 23°.8 
Fort Benton, latitude 47° 26'. “ 2G°.l 
St. Mary’s, latitude 4G° 30'. “ 26°.l 
Lapwai, latitude 46° 30'. “ 36°.9 
Fort Benton will be a little colder, and St. Mary’s milder. 
In the second table, extremes of temperature for each month of 1853, and for three months of 
1854, are given. These follow the same law. 
In the third table, winter temperatures are compared for the last three winters. In this table 
Milwaukie, Buffalo, and Boston are added, to extend this comparison through known districts to 
the Atlantic. The lowest winter temperatures are at Fort Snelling; and the line extending west¬ 
ward from this point has higher temperatures than that extending eastward to the Atlantic, and 
this by a large measure of difference. 
Another comparison is made of stations on the meridians of the Rocky Mountains plateau. 
These are detached and few, but they show striking uniformity of winter temperatures over the 
whole plateau, though the extreme points thus compared differ by twelve degrees of latitude. 
In a general table the amount of precipitation in rain and snow is given, for a series of sta¬ 
tions, in the line of the first temperature comparisons. Fewer stations are embraced than in the 
first case, and Fort Laramie, in latitude 42°, is used as a representative of the district of the 
upper Missouri. It differs only in giving a larger precipitation than is found northward in the same 
longitudes. An important point of comparison here is wanting, in measuring the contrasts in 
precipitation of the mountain regions in different latitudes. Observations of a general character 
supply some facts here, but there are no precise measures. The general laws of climatology 
before referred to embrace all that may be properly introduced here. These results have been 
arrived at by combining with the observations of the exploration those of the Smithsonian Institu¬ 
tion, and those of the military posts reported to the Surgeon General’s office. With these general 
observations, I will proceed to give a more particular view of the manner in which the meteoro¬ 
logical field was occupied, and of the results which have been established. 
For these tables, and for valuable suggestions in reference to the climatology of the region tra¬ 
versed, I am indebted to Professor Blodget, of the Smithsonian Institution. 
The observations for altitude, by the barometer, were made throughout the day at each charac- 
VI f 
