Reports of explorations and surveys, to ascertain the most practicable and economical route for a railroad from the Mississippi River to the Pacific Ocean: Vol. 1, Pt. 2

METEOROLOGY OF ROUTE FROM FORT BENTON TO WALLAH-WALLAH.
The general profile, it will be observed, terminates at Fort Colville. Unfortunately for its continuance, the barometer (the last and best of the four) was accidentally broken soon after leaving
Fort Okinakane. This occurred on the 7th of October, and from that time the observations were
taken with an aneroid. A short experience convinced me that the aneroid, however useful for
other purposes, is nearly valueless in establishing the profile of an extended line of march.
The aneroidal observations, therefore, have been used only to connect the profile of our route
with that of Lieutenant Arnold's party. They occupy only a period of ten days, and that portion
of the route between the Okinakane river and the Columbia at Fort Colville, following in the
Hudson's Bay Company's trail.
The observations for the passes were taken by yourself, with the same barometer as was used
in the observations for the general profile. In calculating the differences of level, I used the tables
calculated from Laplace's formula, published by the Smithsonian Institution.
The point of reference for the maps of the Snoqualme and Nahchess Passes is the mouth of
the Yakima river. In the observations to establish this point, I am indebted to Lieutenant R.
Arnold, third artillery. In the Methow river profile, including the Twitsp and Nahaieelixon, the
point of reference is the mouth of the Methow; and in the general profile the starting-point of the
expedition is Fort Vancouver.
I should have used the level of the sea as given by Nicollet, thirty inches in this latitude, as the
point of reference for the general profile, had it not been for the fact that a series of observations
made at Fort Vancouver, with a standard barometer, under my direction, and which extended
through a period of several months, gave a mean slightly over thirty inches. Fort Vancouver is
one hundred and ten miles from the sea, and, being above the level of the Columbia river, is of
course above the sea level.
By consulting the observations made at Vancouver for Wilkes's exploring expedition, I found
they also averaged over thirty inches.
For this reason, and the additional one that no observations have been made by either branch
of the expedition to establish the usual point of reference, I have taken Fort Vancouver for that
point; it being the lowest and nearest the level of the sea.
I am, Captain, very respectfully, your obedient servant,
SYLVESTER MOWRY,
Second Lieut. Third Artillery, in Charge of Meteorological Report.
Capt. GEO. B. MCCLELLAN,
Corps of Engineers, Chief of Exploring Expedition, Sc. Sac.
36. REPORT OF THE METEOROLOGY OF THE ROUTE TAKEN BY LIEUTENANT C. GROVER, U.S. A.,
FROM FORT BENTON TO WALLAH-WALLAH.
[Extracts of data from journal.]
SIR: After returning from the survey of that portion of the Missouri river intrusted to my
charge, I remained at Fort Benton, on the Missouri, until the 2d day of January, 1854. Up to
this date but very little snow had fallen in this section of the country, and what had fallen covered
the ground but a few days at a time. The weather, as a general thing, had been mild and even,
and the stock of the Fur Company, as well as that of the expedition left here, though depending
solely upon the range for subsistence, and without shelter or care, was in fine condition. The
Missouri had for a short time during the month of December been closed with ice, but on New
Year's day was entirely open, My instructions contemplating the use of dog trains as transportation, every preparation had been completed with the view-dogs purchased, trains prepared,
&c., &c.; but the season had thus far advanced without a sufficient fall of snow to enable me to
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