312 METEOROLOGY. 
mountains. The difference which would be expected from this rate of decrease of temperature 
is 9°.3, showing that, even when the wind blew from the coldest quarter, less cold was 
produced than is usual in places having the same relative altitude above the sea. And as the 
westerly winds are most prevalent, the difference between the climate of the pass and Bitter 
Root valley must usually be even much less. 
It has been found that some snow usually exists in the Nachess Pass from November to May; 
but that being 1,424 feet higher thau the Snoqualmoo, a month may safely be allowed as the 
difference іп the Snoqualmoo Pass, while the period during which more than five feet lies in the 
highest part of it (ten miles, over 2,000 feet) may be reduced to a month. 
In calculating the probable amount of snow which fell in the Snoqualmoo Pass in the winter 
of 1853-54, the mean temperature of that winter should be used instead of the mean of four 
winters, since there is a marked difference between them—that of 1853—54 being 19.2 colder 
than the average, and 4°.4 colder than two winters out of six since 1849, and only 1°.2 warmer 
than the coldest. 
Using the recorded temperature at Fort Steilacoom for 1853— 54, we find that of November, 
1853, was only 09.5 higher than that of December; therefore, if snow fell in December it 
must also have fallen in November. And in this month there was 18.41 inches of rain at 
Steilacoom, while only 20.68 fell in the three following months. This would give for three 
months preceding Mr. Tinkham's journey across the pass in January 26.15, (adding November 
to Captain Humphrey's estimate,) and 12.96 afterwards. By the rule of allowing twelve times 
the bulk of the rain for snow, Mr. Tinkham should have found twenty-six feet, whereas he 
found only six; showing that either 7.2 inches only of moisture had fallen, or that most of it 
(over three-fourths) fell as rain. Admitting that the whole which fell after his crossing was in 
the form of snow, there would be 12.96 feet more; but this would be absurd, since February 
was nearly 10? warmer than January, and there was 1.12 less rain at Steilacoom; taking the 
same proportion as for the preceding months, viz: 1%, making three feet to be added—in all, 
nine feet for the winter. But as the temperature of March was 09,7 colder than December, 
we must admit that three-thirteenths of the moisture of that month was also deposited as snow; 
and then 2.89 inches of rain at Steilacoom would give us + .66 feet more of snow to be added, 
making 9.66 feet from November 1 to April 1. қ 
If November is omitted, so must be December ; and then the moisture which fell before the 
21st of January at Steilacoom, 3.32 inches x 12, would give 3.32 feet of snow, while Mr. 
Tinkham found six feet. Therefore, November and December raust be included. Besides, 
Lieutenant Mowry states that snow falls in these mountains in November, and Lieutenant 
Hodges actually met with a slight fall in the Nachess Pass in September. 
Here we see, too, the necessity of taking into the account the loss by evaporation, thawing, 
and condensation, which goes on even in the coldest weather of the arctic winter. 
Supposing this to account for the difference of the calculated and observed fall from Novem- 
ber 1 to January 21, and admitting the fall from January 21 to April 1 to be three feet, added 
to the six feet found by Mr. Tinkham, there would remain on the ground at the latter date only 
two feet. This would be much further decreased by the greater amount of thawing in the two 
warmer months following January. 4 | 
Or, by another process, we find that the difference between 39 feet, (26 + 13,) the amount 
calculated by the rains of Steilacoom and the true amount, would be in the same proportion as 
that between the amount predicated on the rains previous to January 21 and the actual depth 
