SEXTANT AND PRISMATIC COMPASS SURVEY. 
95 
Any object whose true bearing is east or west must be in the same 
latitude as the place of the observer. 
Any object whose true bearing is north or south must be in the same 
longitude as the observer. 
3. Special survey of a small tract of country, with compass and tape 
only.—Eirst walk over the ground and examine it, with a view to the 
selection of prominent points for stations, and of a level space for the 
E 
AB --Mainline. 
^ ^ ^ j- —Principal triangles. 
C c— 1 Tie line. 
measurement of a base. Having fixed upon a base, A B, set the compass 
up at A, and take a round of bearings to B and other selected stations, 
C, D, E, &c.; then mark A on the field-sheet, in such a position as will 
enable the whole sketch to go on the sheet, and protract the several 
bearings from it. Mark A on the ground with a pile of stones or staff, 
measure the base A B with the tape or by pacing, lay the distance down 
on the field-sheet to the adopted scale, set the compass up at B, and take 
