GENERAL NOTES ON THE CLIMATE. 
569 
tions for August give as the mean per-centage a proportion of saturation but 31 for the hour of 
7 a. m., and but 20 for that of 2 p. m. That of 9 p. m. is 48, and the mean 33, against a mean 
of near 75, or an average in the Mississippi valley and the Atlantic States. The calculation in 
detail would give very low proportions of atmospheric moisture in many cases; and though 
this detail is the only accurate mode of obtaining these proportions, the measures here given are 
a near approximation. 
The quantity of rain is quite imperfectly observed in the record at Fort Benton for several 
months. The amount is apparently small for the year, the winter and spring having evidently 
the greatest quantity, and each near five inches. The rains not measured in summer are not 
noted as profuse in any case; and the distribution seems to partake somewhat of that peculiar to 
the Pacific climates, which have least in summer. On the plains, the greatest quantities are in 
spring, and other seasons are often quite without rain. The strong southwest winds, with the 
high temperature and barometric oscillations then noted at Fort Benton in the winter months, 
prove a connexion to exist with the Pacific climates which does not appear at any other point of 
the plains. In these cases the precipitation is doubtless profuse, in rain or snow, on the mount¬ 
ains of this vicinity. 
The barometric oscillations at Fort Benton and St. Mary’s are also quite conformable and 
identical with each other when projected in curves. They exhibit marked movements in some 
instances quite sudden, and of great range in the winter months, and connect the attendant 
storms beyond a doubt, as belonging to sandar climates at this season. 
The record at St. Mary’s valley requires less analysis and comparison, to illustrate its relation 
to known climates. The position is elevated neariy a thousand feet above Fort Benton, (34L2.5 
feet above the sea,) yet its winter climate is equally mild, and the extremes at that season not more 
severe. In summer, however, the low temperatures of the Pacific coast are felt, and extremes 
occur much greater than those at Fort Benton. April has a mean temperature 6.5 degrees lower 
at Cantonment Stevens, and May 2.5 degrees. In May there is snow on the 7th, as at Fort 
Benton; and on the 28th snow again, two inches in depth, and rains; none of which appear at 
Fort Benton. 
In July snow fell on the 6th in small quantity. In the frequent rains of the summer months 
on the mountains of the vicinity, if not at the post, the sudden changes of temperature and of 
wind peculiar to mountain regions appear characteristic, and to distinguish the climate here at 
that season from that of the plains east of the mountains, as well as those towards the Pacific. 
The quantity of rain is not measured at this post for any part of the period of observation. 
Rains are noted frequently in the remarks, and the number of days of rain and snow may be 
given here, and in comparison with Fort Benton : 
Cantonment Stevens, 
St. Mary’s valley. 
Fort Benton. 
Days rain. 
Days snow. 
Days rain. 
Days snow. 
October_1853, (21 days)..... 
4 
4 
1 
3 
November ...do. 
7 
10 
0 
4 
December ...do.. 
3 
8 
0 
1 
January_1854. 
4 
10 
0 
7 
February_do. 
0 
8 
1 
3 
March_... do... 
6 
7 
1 
6 
April...do. 
7 
2 
4 
0 
May.do. 
8 
2 
4 
2 
June.do. 
10 
0 
6 
0 
July.do... 
3 
1 
2 
0 
August.do... 
7 
0 
4 
0 
September_do. ..... 
10 
0 
12/ 
