INSTRUMENTS USED. 7 



The method to be employed depends upon the purpose 

 of the survey, but no matter what method is used, the 

 survey will fail in its primary purpose if it does not 

 show the location, position, form, and size of the tract 



surveyed. 



INSTRUMENTS USED. 



Three kinds of instruments are used in surveying, 

 viz: For determining azimuth or horizontal angles; for 

 determining grade or vertical angles; for determining 

 distances. The horizontal deflection of a line is always 

 expressed in degrees. The vertical deflection of a line 

 is generally expressed in per cent. The length of a line 

 in Government land surveying is always expressed in 

 chains (66 feet). The altitude above sea level is 

 expressed mfeet. 



The principal instrument for determining azimuth is 

 the magnetic compass, which, although of very simple 

 construction, will be absolutely misleading to anyone 

 who uses it without understanding. Suppose, for 

 instance, a good compass, manufactured and adjusted 

 in some eastern factory or in Europe, should be taken 

 to the Pacific coast. It would undoubtedly indicate 

 the direction of the magnetic currents at any time and 

 place that it might be used, but its needle would not 

 point north and south and probably would not hang 

 level on the center pivot. The latter defect is quickly 

 remedied by moving a little sliding weight, which 

 should be on the south end. of the needle. 



Sight compasses are constructed so that they may 

 be sighted upon a distant object and the magnetic di- 

 rection is determined .by reading the degree indicated 

 on the ring dial by the north end of the needle. 



