Part II. Forest Maps 
SECTION i 
THE TRANSIT 
The transit in general engineering work is the most 
useful and most frequently employed of surveying instru¬ 
ments. It is commonly used to measure horizontal and 
vertical angles, but, having a magnetic needle, it may be 
used to take bearings, and, when provided with stadia 
wires, to measure distances. It may also be used as a 
levelling instrument. A cut of a transit is shown here¬ 
with, also a sectional view through the axis of the same 
instrument. 
The essential parts of an engineer’s transit are described 
below. The telescope is attached by means of a hori¬ 
zontal axis and standards to the upper of two circular 
plates. The two plates move freely on one another, the 
lower being graduated, while the upper has a vernier 
which allows readings to be made with accuracy. A 
compass circle is also attached to the upper plate. A 
clamp fixes the upper to the lower plate, and a tangent 
screw secures a slow adjusting movement between the 
two. A similar arrangement is placed between the lower 
plate and the head of the instrument. 
The whole instrument is supported on a tripod ; levelling 
screws serve with the aid of cross levels to fix the plates in 
a horizontal position; and a finely turned spindle and socket 
arrangement guides the plates in their movement on one 
another. By means of a plumb line attached to the lower 
end of the spindle the instrument may be set with its axis 
exactly over any desired point. 
1. Adjustments of the Transit 
The object of these adjustments is to cause (1) the 
instrument to revolve in a horizontal plane; (2) the line 
of sight to generate a vertical plane when the telescope is 
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