SURVEYING 53 



and fractions of degrees, which enable the angle between 

 lines of sight in different directions to be measured. This 

 device is especially useful in laying off right angles, as well as 

 in obtaining the angle between two sides of a tract of land, 

 and between lines of drains in laying out drainage systems. 



The Compass. A level may be provided with a compass 

 box containing a magnetic needle, which will enable the angle 

 to be measured between any line of sight and the north and 

 south as indicated by the needle. In construction, the mag- 

 netic needle is a fine hardened piece of steel carefully balanced 

 and hung on a delicate pivot and so arranged as to swing 

 within a graduated circle. In order to protect the pivot 

 while the instrument is being carried about, a little device 

 is provided to lift the needle from the pivot. In most 

 localities the needle does not point truly north and south, 

 inasmuch as the magnetic pole does not always lie due north; 

 and furthermore, the location of the magnetic pole varies 

 from time to time. If the true north is desired, it is neces- 

 sary to make the corrections for the location of the magnetic 

 pole. This variance from the true north, or meridian, is 

 called the declination of the needle. In reading the needle, 

 if no correction is made, it is customary to indicate that the 

 reading is magnetic (Mag.). 



The Bearing of a Line. The direction of a line is called 

 its bearing; in other words, the bearing is the angle that a line 

 makes with the direction of the magnetic needle. If the 

 direction of a line, beginning with the instrument, lies within 

 90 degrees to the right or the left of the needle, it is said to 

 have a north bearing, or a northing; and likewise, if it lies 

 within 90 degrees of the true south, either east or west, it is 

 said to have the south bearing, or a southing. If the line 

 lies to the east of north, it is also said to be east, and if to the 

 west, it is said to be west, and is so designated following the 



