GENERAL NOTES ON THE CLIMATE. 567 



Mowry gives some valuable temperature observations on this eastern base of the Cascades, and 

 his condensed notes of results are very well sustained by all the observations. A continuous record 

 at. Fort Okinakane or Fort Colville would, apparently, have many features in common with one 

 at St. Mary s valley for the colder months ; yet, for the summer, there must be some prominent 

 points of difference. Each of these districts is decidedly separable from the immediate coast of 

 the Pacific west of the mountains, and has little in common with it at any season. 



The comparisons which would illustrate the relation of the climate on the western border of the 

 plains of the Missouri to those of the east, or of known points on the Mississippi valley, are first 

 necessary, and they may now be made directly with these points for the same months. The 

 record at Fort Pierre unfortunately does not commence until nearly the last of the months observed 

 at Fort Benton, and it cannot, therefore, be introduced at the point where it is most desirable. 

 The elevation of Fort Benton above the sea is 2,GG2.9 feet by the mean of all the barometric 

 observations taken there.* The most conspicuous feature of the temperature of the post is its 

 near agreement with that of posts on the eastern border of the plains even in lower latitudes, 

 as Forts Snelling and Leaveriworth from the commencement of the record to the close of Octo 

 ber. For the portion of September observed, and for the whole of October, it was warmer than 

 Fort Snelling, and but little cooler than Fort Leavenworth. The extremes of 80 for the highest, 

 and 10 for the lowest degree, are nearly the same as at Fort Snelling, where the lowest degree 

 in October is 8 the lowest at Fort Leavenworth being 22. The lowest at Fort Laramie for 

 October is 20. At the close of the month there were severe storms, with but little rain or snow, 

 however. 



For November the range of temperature was low, and on six days at or below zero. The 

 monthly mean was ten degrees less than at Fort Snelling, and 24.5 less than Fort Leavenworth. 

 It is also 14.5 less than that of Cantonment Stevens, on the west of the mountains. The fall of 

 the temperature as winter approaches appears to be much more abrupt east of the mountains in 

 his latitude than at the west, or in the vicinity of the great lakes. There were few storms and 

 very little snow. 



The record for December is quite anomalous, and, if not affected by position of the thermome 

 ter, gives an extraordinarily high temperature. At all other posts of the Northwest Forts Snel 

 ling, Kearney, Laramie, &c., east of the mountains, and at Cantonment Stevens and Olympia on 

 the west the temperatures of December are several degrees below those of November, while, as 

 recorded here, December is 13.5 warmer than November. The record is very nearly the same 

 as that at Fort Laramie for the same month, though colder than this post in November by 22 in 

 the mean temperature. A peculiarity so remarkable should be verified in the most complete 

 manner, as it would go far to prove the distinctive features of the climate of the northern portion 

 of the plains east of the mountains, to be quite separable from those farther south and east. The 

 changes occurring at every point from the longitude of Fort Kearney eastward are so far asso 

 ciated as to produce marked correspondence among all the stations of a very large area. The 

 ordinary relation of ihe temperatures of the winter months is sometimes reversed, but in every 

 case the whole country participates in some measure in the change. 



At Great Salt lake, as observed by the Central Survey, the temperature of December is much 

 above that of January following, and also apparently much above the average, though there 

 are but few observations in the same month in previous years with which to compare it. In 

 1854 the mean of December at Great Salt lake was 31.3 against 41.5 in 1853. These facts 

 favor the view that the temperature changes of this meridian may not necessarily be associated 

 with those of either side of the mountains at great distances. 



* The comparison of the barometer used with a standard is not given in connexion with the observations. It was a syphon, 

 by Green, No. 769, and it is only known that it is reported as in good order by Mr. Doty. 



The determination of altitude is made by assuming a mean barometric reading of 30.000 inches at sea-level, the reading reduced 

 to freezing point, and a mean air temperature of 50. 



