396 METEOROLOGY OF ROUTE FROM FORT BENTON TO WALLAH-WALLAH. 



The general profile, it will be observed, terminates at Fort Colville. Unfortunately for its con 

 tinuance, 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 often 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, fyc. fyc. 



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 transport 

 ation, 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 



