12 
MAPS ACCOMPANYING THE REPORT. 
travelled were measured by an odometer, until tlie wheels were necessarily abandoned among 
the Cascade mountains ; and then carefully estimated from the time and supposed rate of travel. 
The courses were determined by prismatic compasses. The latitudes of a large majority of the 
camps were fixed with considerable accuracy by astronomical observations. Several camps 
before camp 17 were connected with San Francisco by chronometric differences, and the longi¬ 
tude thus approximately determined. An unfortunate accident, in Canoe Creek valley, however, 
rendered the chronometers worthless for this purpose during the remainder of the survey, and 
compelled us to depend upon our courses and distances, checked by the latitudes of the camps, 
and by a system of triangulation among the prominent mountain peaks near the trail. The 
assumed longitudes of a few important points upon the route seem to require particular ex¬ 
planation. 
As Fort Reading was the point from which we started to leave the settlements, great care 
has been taken to determine its longitude as correctly as possible. Col. J. C. Fremont, on his 
map of California and Oregon, places the point of Cow Creek, upon which the fort is now 
situated, in Long. 122° 6' 50" west from Greenwich. On the Land Office map of 1855, it is 
placed in Long. 122° 11' 9". On the map of Lieut. E. G. Beckwith, 3d artillery, illustrating 
his exploration for a Pacific railroad route near the 41s.t parallel of north latitude, it is placed 
in Long. 122° 5' 8". The four chronometers used on our survey apparently preserved their 
rates unchanged during our march up the Sacramento valley, as they all agreed very well with 
each other. The longitude of the fort, determined by their mean corrected difference from local 
time, was 122° 10' 50". As this differs only three-tentlis of a mile from that given by the Land 
Office map, it has been adojffed as correct. It places the fort 3.5 miles west of Col. Fremont’s 
location, and 5 miles west of that of Lieut. Beckwith. 
The following method has been adopted to fix the longitude near the northern terminus of the 
survey. The longitude of Salem has been determined with considerable care, under the direc¬ 
tion of the surveyor general of the Territory, both by astronomical observations and by 
measuring a line to the coast, and thus comparing the result with the work of the United States 
Coast Survey. It is 122° 53' 43" west from Greenwich, as I was informed, when at Salem, by 
Mr. Hervey Gordon, deputy surveyor. He also told me that Mount Hood and Mount Jefferson 
had been carefully located by bearings taken from well determined points with the solar compass. 
I therefore made a preliminary plot of the northern portion of our survey, based upon the Land 
Office positions of these peaks as fixed points. As over fifty bearings had been taken to each 
mountain, many of which were from points where the latitude was astronomically determined, 
I was enabled to slightly correct the relative position of the two peaks. The map was next 
replotted with respect to these new positions. The result was highly satisfactory, as the compass 
work fitted admirably, and the longitudes of two points in Des Chutes valley, determined by 
Col. Fremont in 1843, by observing the occultations of Jupiter’s satellites, were almost precisely 
the same as those of the corresponding points on the plot. It is thought that this coincidence 
renders it very improbable that any important error in longitude has been made. 
The latitude of Fort Dalles was astronomically determined, and numerous bearings upon 
Mount Hood and the neighboring peaks enabled me to fix its longitude very closely. It was 120° 
58' 30". This location is about three miles west of that found by Col. Fremont, by observing 
an emersion of Jupiter’s second satellite, on November 5, 1843. He afterwards observed the 
emersion of Jupiter’s third satellite, on November 20, 1843, at the same spot, and published 
the data obtained, without, however, giving the deduced longitude. I find, by computation, 
