110 
KIRTLEY F. MATHER 
pivot point on an arrow and the sun- time point’’ on a latitude 
arc are on a line parallel to the shadow cast by a plumb-line 
upon a level table the arrow points true north. A copy of this 
chart and full directions for its use may be found in Topographic 
Instructions of the United States Geological Survey, pp. 136 to 
141.8 
Lining in the station. After the table has been properly 
oriented at a station, the location of which has been plotted on 
the map, the bearing of any visible object may be drawn directly. 
The alidade is moved until the straight edge touches the side of 
the needle-hole or pencil dot representing the occupied station 
and the vertical cross-hair in the telescope bisects the distant 
object, the bearing of which is desired; a line drawn along the 
straight edge will then represent the compass-bearing plotted to 
position on the map under construction. 
The best method to pursue in lining-in a distant station is to 
grasp the ends of the alidade base with either hand; shift the 
instrument until the line of sight through the telescope falls upon 
the desired objective and the fiducial edge rests within an inch or 
two of the dot locating the occupied station; then move the 
alidade diagonally forward and to the right, keeping the vertical 
cross-hair on the distant object, until the ruler edge touches the 
proper point. If the alidade is equipped with a parallel-edge 
ruler, it is only necessary to place the instrument somewhere 
near and to the left of the plotted point in such a position that 
the vertical cross-hair cuts the distant station; then push the 
parallel straight-edge outward until it touches the proper point. 
Some surveyors make it a practice to stick a. needle vertically 
into the plane table at the point representing the occupied 
station, and to pivot the alidade on the needle when lining-in a 
station. This practice is not recommended. Although it is an 
easy way for the novice to increase his speed, it involves inaccu- 
racies of considerable import. If the needle is inserted far 
enough to hold its upright position, it makes a hole several 
times as large as necessary; the point becomes a space which on 
® Government Printing Office, Washington, D. C., 1918; price 35 cents. 
