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Surveys with Sextant and Prismatic Compass.* 
By General Sir C. W. Wilson, r.e., k.c.b. 
A traveller who intends to devote a portion of his time to the survey 
of the country he is about to visit, should consider before leaving home 
what he is going to do, and how he will do it. The character of the 
proposed survey, the projection to which it is to be referred, the scale or 
scales to be adopted, the instruments to be used, should be carefully thought 
over before commencing work, and there should be no hesitation when 
once upon the ground. A decision on these points depends on various 
con siderations—such as the time and means at the disposal of the traveller, 
the object in view, the nature and geographical position of the country, 
Ac.; and the following notes are confined to a few hints which may be 
useful in the field. 
Projection *—'When the extent of country to be laid down is small, it 
may be treated as a plane-surface; but when it is considerable, allowance 
must be made for curvature, and some projection of a portion of the 
sphere, adopted. The projection should be selected with reference to 
the latitude and local peculiarities of the country to be surveyed; the 
sheet should be prepared before leaving home by a competent draughts¬ 
man, and two or more copies of each taken, packed in a round tin 
plan-case. It may happen, however, that a projection has to be made in 
the field, instruction for which will be found, p. 58 et seq. 
Scale.—Pox the fair plan, a scale of 10 miles to an inch is recommended, 
for the field sketch or outdoor-work, a scale of 2 miles to the inch; or, if 
much detail is required, of 1 mile to the inch. The scale of 2 miles to 
the inch has this advantage—that the ordinary sketching-card 12" x 15" 
will contain sufficient ground—24 miles x 30 miles—for the day’s work 
and most of the points to which bearings are taken. 
The classes of Survey to which attention may be directed are—1. A 
* It will be understood, that if a small theodolite can be carried, the work of 
surveying will be greatly facilitated. 
