SURVEYING WITH THE THEODOLITE. 
117 
The following is an example of the first method, traversing from 
A to D. 
Fig. 1 . 
Set the theodolite up at A (Fig. 1), level it, and adjust it for parallax in 
the manner described, p. 26. Set one of the verniers of the vernier plate 
to 360° and clamp it. Loose the clamp of the lower plate, direct the 
telescope on the point Y chosen for zero, and, using the lower set of 
screws, bisect it with the cross threads in the diaphragm of the telescope 
and clamp it firmly. Release the compass needle and note the bearing. 
Now, keeping the lower clamp fast, release the clamp of the vernier plate 
and take a round of angles to all objects the positions of which it is 
desired to fix, only using the upper set of screws; then turn the telescope 
on the next forward station, B, bisect it with the cross threads of the 
diaphragm, using only the upper set of screws. Note the reading of 
the same vernier which was set to zero, and keeping the plates clamped 
at this reading carry the theodolite to the next forward station, B, where 
it must be set up, the lower clamp being loosened for levelling it. 
With the two plates still clamped together, turn the telescope back on A, 
using only the lower set of screws. When this is done, release the clamp 
of the vernier plate, and take a round of angles as before, finishing with 
