REPORT. 
CHAPTER I. 
Methods pursued in determining the Data upon which are based the Maps and Reports of 
the Survey. 
To enable the department to judge advisedly of the amount of confidence due to the results 
of an exploration of this character, it would seem proper to set forth the organization of the 
exploring party, and to describe in full the instruments used and the methods pursued in 
determining the data upon which these results are based. 
As the object of this exploration was eminently practical in its character, and had in view 
the investigation of a specific question, I have thought it advisable, in determining upon a plan 
for the report, to give the prominent place to the practical results which have a direct hearing 
upon the construction of the railroad, and to set them forth under proper heads, as briefly as 
is consistent with clearness. For this purpose I have carefully avoided embarrassing the 
subject with a narrative of the daily incidents of the expedition, which must he more or less 
irrelevant, or involving it in obscurity by the introduction of detailed descriptions, under scien¬ 
tific and technical names, of the specimens collected in the various departments of science. I 
have only introduced into the reports such extracts from these subjects as are necessary to 
illustrate some point having an immediate and important hearing upon the question of the 
railroad, and have collected into an appendix the diary of the expedition and the reports upon 
the geology, botany, and natural history of the route. 
Method of determining the geographical position of the route .—Of this duty I took charge 
myself, and the following plan was adopted: Seven principal points were selected along the 
line, as nearly at equal intervals as it was possible to place them, and at each of those points 
the latitude and longitude were carefully and absolutely determined, by a complete series of astro¬ 
nomical observations. The sextant was the only instrument I had for this purpose, and it was 
therefore necessary to determine the longitude by the method of “lunar distances.” At least 
seventy lunar distances of the sun, and of stars east and west of the moon, were observed at 
each principal point; and the latitude was determined in all cases by at least one hundred and 
fifty altitudes of stars north and south of the zenith. At each of these points the chronometer 
was carefully rated by observing equal altitudes of the sun, and altitudes of east and west stars, 
for several successive days. Twenty intermediate points were determined along the line by at 
least sixty altitudes of north and south stars for latitude, and twenty altitudes of east and west 
stars for the error of the chronometer. As the rate of the chronometer was carefully deter¬ 
mined at each principal point, and the chronometric longitudes of intermediate places were 
referred directly and at short intervals to the points thus absolutely determined, the time obser¬ 
vations may be considered as furnishing at least very close approximations. Twenty-seven 
points along the route, at intervals not to exceed twenty-five miles, were thus astronomically 
determined ; and as the observations exhibit no error on tbeir face, and the results determined 
by the computations of several able and experienced computers are in all respects satisfactory, 
the position of the line of survey may be considered fixed with some considerable degree of 
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