36 



■(Implements. 



other plantations may be located by this simple means as 

 correctly as if a compass or transit were used. 



The compass is used for measuring angles. It consists 

 of a horizontal plate with two vertical arms provided with 



V hair-sights, and a circular box 



with a graduated edge and a 



magnetic needle hanging on a 



fine point in the centre. The 



blue end of the needle always 



turns due north, or as nearly so as 



necessary for all practical purposes. 



By means of a capstan screw the varia- 



F1Q. 9.-COMPAS ti()n of tbe Qeedle can be Bet off rpj^ 



instrument is attached to a ball-joint and socket for a sim- 

 ple stake or " Jacob's staff." It can also be used with a 

 tripod for more exact measurements. When in use it is 

 placed above a given station, as A in Fig. 10 ; the joint 

 upon which the needle is hung should be precisely above 

 that station. Adjusting the instrument in a level and ver- 

 tical position, we point the arms in the direction of B, 

 where a flagstaff has been placed previously, and bring 

 the hair-sights to bear on the staff. Now it is easy to 

 count the number of degrees between the blue point of 

 the needle and the line indicated by the direction of the 

 two arms of the compass. The angle is noted in the field- 

 book, we measure the distance from A to B with a tape-line, 

 and shift the instrument to B and proceed in the same 

 manner there. More often the instrument is placed only 

 on every other station, and the length and degree of the two 

 lines are taken from that point, as B and E in Fig. 10. A 



