106 METHOD OF COMPILING THE MAP. 
in from my map from the mouth of the Big Muddy to the Big Nemeha.* Below that it is 
taken from the Land Office surveys. From the Big Muddy to Fort Benton it is from reconnais- 
sances made under Governor Stevens. | 
On Governor Stevens’ explorations in 1853, no observations were made for longitude. The 
route was determined by compass courses and odometer distances, checked by observations for 
latitude between the mouth of the St. Peter's river and Fort Walla-Walla. The longitude of 
Fort Walla-Walla, according to Colonel Frémont, is 118? 32', but he made no astronomical 
observations at this point. According to Captain Wilkes it is 118° 47’ 45". The means by 
which this was obtained will be found in the following letter, which Captain Wilkes was 
kind enough to send me in answer to certain inquiries. His determination, as "AB in his 
letter to me, was X dus 
WASHINGTON CITY, July 5, 1854. 
Dear Sir: Your letter of June 29 would have been answered sooner if I could have found 
the observation by which the position of Walla-Walla was determined. 
The position I assign to it is, latitude 46? 02' 48" north; longitude 118? av 45" west. 
The result of three days' observation deduced from ان فة‎ ; these were made by Lieu- 
tenant Johnson, of the expedition, who had charge of the party, and were calculated out 
under my own examination of the notes. The position was also determined by bearing or 
angles on three mountain peaks,t which gave a very near accordance in the result. I have 
always felt great confidence in the result. I gave them at the time a very careful examination, 
and think Lieutenant Johnson made them under favorable circumstances. Mr. Drayton, who 
also visited Walla-Walla on the survey of the river up to that point, agrees in his determina- 
tion with Lieutenant Johnson at this p their observations were intended to serve as 
checks upon each other. 
I am, very respectfully, your obedient servant, 
CHARLES WILKES. 
Lieutenant G. K. ee 
l Engineers, Washington. 
The و ن را‎ of Captain Wilkes was also adopted by Mr. Lambert, (Governor Stevens’ 
topographer,) who constructed his map in this office. He says of the route of the main line of 
Governor Stevens’ survey, in his report on topography, (Pacific Railroad Surveys, quarto 
edition, 1st volume, page 176, Governor Steven’s Report): ‘‘It is satisfactory to know that 
the survey, as it was first plotted, independent of correction by astronomical points, but con- 
nected by those of Captain Wilkes and Professor Nicollet, was only ten miles in error, being 
in excess." As far west as Walla-Walla, Governor Stevens' route, as mapped, is, therefore, 
copied on the general map; but west of this, along the Columbia, it has been subjected to 
some modifications by the Land Office surveys and the reconnaissance by Lieutenants Williamson 
and Abbot, in 1855. 
The Yellowstone river, as far up as the mouth of "Powder river, was token from my recon- 
naissance in 1856. Powder river is the same as the Warharsa on Lewis and Clarke's map. 
Any one will, I think, be convinced, who examines the maps. and reads Lieutenant Mullan’ s 
* My transit observations at Fort Sandali in 1857, show the position of the fort, as ۰ thus laid down, (longitude 98° 
36’,) to be nearly correct. €— 
+ This required Captain Frémont's reconnaissance along Snake eer to be elongated to the amount of 16/ between Fort 
Walla-Walla and Fort Hall. 
———Ó‏ زو سوبس کے 
