314 ` METEOROLOGY. 
estimate from the amount of moisture in winter as we have done there, especially since we find 
that at Fort Benton, with a winter 5° colder than on the Great Plain, the proportion of snow 
to moisture was only 18.5 to 5 inches, while at Fort Snelling we allow 50 to 5 inches. 
The register of rain and snow at Fort Benton for one year, although imperfect, still shows 
that less moisture is there deposited than at Fort Laramie; and although the amount is much 
greater west of the Rocky Mountain divide, as shown by the comparison of the number of days 
in which rain or snow fell at Cantonment Stevens, yet none of the parties who traversed that 
part of the route in any winter month found snow enough to interfere with a railroad. 
OBSERVATIONS ON THE ISOTHERMAL CHART. 
The isothermal lines east of the Mississippi are copied from Blodgett’s Climatology of the 
United States, published in 1857. These do not differ much at the sea level from those deter- 
mined by the Smithsonian, and published in the Patent Office Agricultural Report for 1856, but 
are curved on the land to conform generally with the undulations of the surface, their correct- 
ness being tested by numerous and long-continued observations at fixed points, by which the 
local influences, independent of latitude and altitude, may be considered pretty well established. 
The direction of these lines west of the Mississippi and north of latitude 50° have been deter- 
mined partly from the same and partly from data additional to those used by Mr. Blodgett, and 
they are found to vary so much from his conclusions that a statement and discussion of them is 
rendered necessary. 
1. Red River of the North.—Mr. Blodgett gives in his table of statistics only seven months’ 
observations at Pembina, latitude 49°, and at such irregular intervals that only part of them 
сап be used for computing the means for spring and summer. А year’s observations at Fort 
Garry, latitude 50° 15’, near the mouth of the river, are used in this computation, showing a 
difference of about four degrees for the two places at corresponding seasons, which, being about 
that due to latitude in this region, makes the mean for winter reliable as the true winter climate 
of the place. The following table shows the comparative results thus obtained : 
5 " E : 
E £ E sb - E S d 
чә aD 2 Я з = ы @ 
Е E = E g E B B 5 
1 d 4 E E < Е > ж 
o Oo x Feet. о о о эл 
Fort Snelling ..-............... 44 53 | 93 10 820 | 45.6 70. 6 45.9 16.1 | 44.6 | 354 years. 
Fort Ripley...- 46 19 | 94 19 | 1,130! 39.3 64. 9 42.9 10. 0 39.3 | 6 years. 
Pembina 49 00| 97 001 900| 343 | 71.7 --| 7 months. 
Fort Garry 50 15 | 97 00 860 | 35.8 67.8 | 40.8 6.9 37.8 | 1855-'56. 
8 The lower altitude would account for the mean annual difference being in favor of Fort Garry 
over Fort Ripley, even supposing that the summer temperature is not too great, which it may 
very possibly be from local circumstances. 
The table for Fort Garry is copied from the “ Report of the Exploration of the country 
between Lake Superior and the Red River Settlement,’’ Toronto, 1858. 
The next points in the lines in which alteration was found necessary are those where the 
isotherms for winter (isochimenes) strike the Missouri between the mouth of the Platte and 
Fort Union. The materials at Mr. Blodgett’s command were very imperfect for this portion, 
