82 A MANUAL FOR NORTHERN WOODSMEN 
and read the final angle. If the instrument has two ver¬ 
niers both should be read. It is customary to record the 
reading after turning the angle once, as a check on 
the repeated reading. The true reading is the average of 
the values obtained for the angle with telescope direct 
and telescope inverted. 
To Prolong a Straight Line. Set up the instrument over 
the forward point and sight the telescope on the rear one. 
Set both clamps, revolve the telescope on its axis, and set a 
new point as far ahead as convenient or desired. 
More Accurately. With the telescope in its natural 
position, turn on the rear point, clamp, revolve the tele¬ 
scope as above, and set a stake and tack at the forward 
pointing. Then, leaving the telescope inverted as it is, 
swing tjie plates around half a circle and set on the rear 
point again. Revolve the telescope, and again sight at 
the forward point. If the two pointings ahead do not 
coincide, set a tack half-way between the two and it will 
be in the line desired. 
To Measure a Vertical Angle. For this purpose the ver¬ 
tical circle must be adjusted so as to read zero when the 
telescope is level, or, if it is not adjustable, the error of its 
reading must be obtained, as explained under adjustments 
of the transit. Then the angle of elevation or depression 
to any point may be measured by sighting the telescope 
upon it and reading the vertical angle by means of the 
vertical circle and its vernier. 
To Survey a Piece of Ground with the Transit. Set 
up on the initial point of the survey, turn to the second 
point, read the bearing of the line, recording it for a check 
on later angles, and measure the line. Set up over the 
second point, set the two plates to read zero, and clamp 
them together; then turn the telescope at a rod held ver¬ 
tical and carefully centered over the first point. Set the 
lower clamp and loosen the upper one, swing the tele¬ 
scope with the upper plate around until the third point is 
sighted, and read the angle so turned. Read the bearing 
for a check, and measure the line. Proceed in this way 
until all the angles have been turned and all the sides 
measured. Interior angles should always be read, though 
