The principle is
one which is occasionally employed for setting out circles with a
pocket sextant, viz., the property of a circle that the angle in a
segment is constant. The leading feature of the invention is the
arrangement of scales, which enables the operation of setting put
large curves for railway or other work to be carried out without
requiring any calculations, thereby enabling any intelligent man to
execute work which would otherwise call for a knowledge of the use of
a theodolite and the tables of tangential angles.
[Illustration: FIG. 1--PERSPECTIVE VIEW OF INSTRUMENT MOUNTED ON A
STAFF.]
The instrument is intended to be thoroughly portable; so much so,
indeed, that it is not necessary or even desirable to use a tripod. It
may be held in the hand like a sextant, or may be carried on a light
staff. The general appearance is shown in Fig. 1. It will be seen that
a metal plate, on which two scales are engraved, carries a mirror at
one end and an eye piece at the other.
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