METEOROLOGY. 311 
From these data a good estimate may by formed of the temperatures of the mountain passes 
between each set of posts of observation, by allowing 3° decrease of temperature for each 
1,000 feet elevation, as estimated by Professor Henry, of the Smithsonian Institution. From 
this calculation the following table is constructed: 
" e 
© = 
: E 5 
ғ 3 i ot 
3 E. Е Comparison оп route by Cadotte’s and 3 5 3 3 
S $ © 4 8 5 $ 
ilf: ЕЕ Sé e bti 77 
& a E = н 4 E & д 
t 12 р $9..1 ^ 3 E: - "EB 
& LB 1-451184 08 JURE M 
Feet. | Miles. | Feet. | Miles Feet. Feet, | Miles. | Ғе, | Miles | Feet. 
2,780 95 6,044! 95 3, 284 | Altitude 4,519 | 330 | 8,000 | 95 | 4,500 
о о о о о о 
2600 уде T1704... 27.0 | Winter temperatures of 1853 and 1854..| 30.2 |...... ТТБ {а-а 23.0 
In the latter case the interval between the two posts, which exceeds 6,000 feet in altitude, 
is over two hundred miles, all of which would have a winter temperature ranging between 
159.1 and 239.5. 
On the other hand, only 165 miles on the northern route exceed 3,000 feet in altitude, having 
a winter temperature between 17°.0 and 26°.0, and only six miles exceed 5,000 feet. 
The two coldest days in January, 1854, furnish a good evidence of the general correctness of 
the rule followed, as here shown: 
CADOTTE'S PASS. FORT BENTON. 
Date. ; Difference. Wind. 
Sunrise, noon, and | Та. m., 2 and 9 
p. m. 
o о о 
January 12,1854... —8 —10.3 7.1 NE.NW. 
January 13,1854... —22 —13.3 8.7 NE. 
SNOW AS AN OBSTRUCTION TO THE RAILROAD ROUTE. 
Details of the information in regard to snows in the Cascade mountains are given in Volume I, 
and more recent observations do not show any probability of their being under-estimated. The 
winters must affect the temperature of the passes sufficiently to prevent 
great mildness of the 
s frequently take 
the constant accumulation of snow for more than one winter month, while rain 
their place. Compared with Steilacoom, where the mean winter temperature is 399.5, that of 
ould be at least 29°, while for much of the time it would rise above the 
freezing point and cause thaws or rain. It has already been shown that the difference of 3° 
for each 1,000 feet was too great, as determined by actual observation of the coldest days of 
t Fort Benton and Cadotte’s Pass; and the great rarity of cold northeast winds, 
ence there still less than in the Rocky 
Snoqualmoo Pass sh 
January, 1854, a 4 
as we approach the Pacific coast, must make the differ 
