PLANE TABLE SURVEYING. 
97 
The following symbols are recommended for adoption: — 
Z *s signifies angles. 
A ^ station in the triangulation. 
© 
33 
fixed by latitude. 
33 
S3 
longitude. 
© 
33 
33 
lat. and long. 
>3 
33 
true bearing. 
>i 
33 
33 
right tangent. 
K 
3’ 
33 
left 
Surveying with the Plane Table. 
(For a description of this instrument , see p. 40.) 
The first thing for the traveller to decide on, in commencing a survey, 
is the direction and extent of his base; and, as no special instructions 
can be given for a base suitable for all surveys, it is a matter in which 
he must exercise his own discretion, bearing in mind the following 
points: that the length of the base line should not be out of proportion 
to the distance of the points to be fixed, and that the first points to be 
fixed must be visible from both ends of the base line. The length of the 
base should be accurately measured, or determined by observation. The 
direction of the base line must depend on the positions of the points 
to be fixed, as, when the angles subtended are either too obtuse or too 
acute, a small error in the alignment will produce a large one in the 
survey. 
Having decided on a base line, call it A B (Fig. 1, p. 98), set up the 
plane table over A, and arrange the board so that the direction of a b will suit 
the position of the first portion of the survey. Level it by moving the legs 
of the tripod, and using the circular level on the ruler. Clamp the table, 
and mark a point on the paper in any convenient position, to represent 
A on the ground, call this a. Stick a pin in at a, and, placing the 
fiducial edge of the ruler against this pin, turn the ruler about until Urn 
other end of the base, B, can be seen through the slit on one of the alidade 
sights, on the wire of the other sight, then draw a line along the fiducial edge 
VOL. I. H 
