THE SURVEYOR S COMPASS 3 



the compass to any given object referred to the meridian. 

 It is read as so many degrees from the N or S direction, 

 up to 90; as, N 10 W, S 88 15' E. The graduations on 

 a surveyor's compass are commonly in half degrees, but it 

 is usual, if necessary, to set by estimation quarter degree, 

 or 15', courses. A bearing can be set, however, with a 

 surveyor's compass in first-class order, to about 5'. 



A compass needle that is in good working order 

 takes some little time to settle, and its condition may be 

 told by the freedom and activity with which it moves. 

 Time can be saved in setting it by checking its motion 

 with the lifting screw. In its final settlement, however, 

 it must be left free. For important bearings, it is well to 

 let it settle two or more times independently. 



A glass plate covers the compass box and two small 

 levels placed at right angles to each other are used to set 

 the instrument in the horizontal plane. It is very de- 

 sirable that the box of a compass employed for woods 

 work should be as nearly watertight as possible. In 

 general make-up, the instrument is subject to considerable 

 variation. 



The plate of the Plain Surveyor's Compass is prolonged 

 in the north and south direction into arms on which the 

 sights are supported at a distance of twelve to sixteen 

 inches apart. The actual sighting is done through fine 

 vertical slits, and round apertures placed at intervals along 

 these are convenient for finding objects and for getting the 

 instrument approximately in line. 



The Vernier Compass has the circle and the sights 

 upon separate plates which may be turned on one another 

 for 20 or more. Its advantage consists in the fact that 

 declination, or a change in declination, may be set off, 

 and the courses of an old survey set directly, or lines re- 

 ferred to the true rather than the magnetic meridian. 



The Folding-Sight Compass possesses the advan- 

 tages of light weight and the utmost compactness, and is 

 therefore popular among woodsmen. The sights are set 

 upon the edge of the compass box, and fold down across 

 its face when not in use, the whole instrument with its 

 ' mountings slipping into a leather case which may readily 



