USE OF COMPASS 
from its pivot and clamped against the cover glass. This clamp is 
usually so arranged as to be brought into action as the case is closed 
and so lift the needle from its pivot when the instrument is not in 
use, thus saving the pivot from unnecessary wear and keeping the 
needle in better condition. 
Hand compasses are made in a variety of forms and sizes. 
The larger ones with longer needles are more carefully made and 
much better. There are two general kinds: 
1. The Plain, Box or Pocket Compass in which the needle moves 
within or above a fixed dial all parts of which are open to view. 
Such instruments are often of watch form and not necessarily 
shaped like a box. They often have folding sight vanes on the 
N.-S. line; that at the south end with a narrow vertical slit; that 
at the north end with a vertical hair, thread or wire. 
Fig. 14. Types or Compasses— Box Compass; Prismatic Compass; Brunron’s 
Pocket TRANSIT 
2. The Prismatic Compass in which the dial is attached to and 
floats with the needle and often only a small part of it is exposed to 
view. There are usually sight vanes, and on the south one there 
is a prism so placed as to refract the dial to the eye and make it 
possible to sight the direction and read the dial at the same time. 
In another form a mirror in the cover serves the purpose of the 
prism. 
35 
