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 results 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 band 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, (hough made and their general character known, not being at hand. 



It will 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 &quot; 23.8 



Fort Benton, latitude 47 26 2G.l 



St. Mary s, .latitude 46 30 &quot; 26.l 



Lapwai, latitude 46 30 &quot; 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 ihose 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- 

 IT/ 



