LESSON 8 
UsE oF Compass 
N the simplest paced surveys no compass is used, 
the cardinal directions being known with suffi- 
cient exactness. However, as paced or taped 
surveys become more elaborate the point is soon 
reached where directions have to be determined 
more carefully and horizontal angles read. The 
use of a hand compass is then the next step. 
The present lesson takes up the construction and use of the compass 
in its simpler forms. 
Compass Construction 
The essential part of a compass is a magnetized needle balanced 
on a vertical pivot. This needle when given its freedom will swing 
horizontally till one end points toward the magnetic but not the 
true north. 
The ends of the needle are marked in some way to distinguish 
them; sometimes one end, — usually the north, — is colored blue, 
sometimes a short transverse bar is placed in the north end, some- 
times the south end has a small coil of wire wound around it to 
balance the dip of the needle. Usually the needle is deeper than 
wide so as to balance better. 
The needle swings within or over a circular dial which is divided 
into 360 degrees. The unit of graduation is usually one degree, 
sometimes one-half degree or on small instruments two or five de- 
grees. 
The needle oscillates a good deal and comes to rest slowly. 
In order to check its motion and bring it to rest more quickly a 
small clamp is usually provided by which the needle may be raised 
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