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. The mirror is mounted on a
metal plate, which is shaped to a peculiar curve. A clamp and slow
motion provide for rapid and for fine adjustment. The eye piece is set
at an angle, and contains a half silvered mirror, the upper portion
being transparent. This allows direct vision along the axis of the eye
piece, and at the same time vision in another direction, after two
reflections, one in the eye piece and the other at the adjustable
mirror. Fig. 2 is an outline plan of the instrument when closed. In
the first form of the instrument only one mirror was provided, but by
the double reflection in the improved pattern, any accidental twisting
of the rod or handle produces no displacement of the images, since the
inclination of one mirror neutralizes the equal and opposite
inclination of the other. No cross line is required with the new
arrangement, since it is only necessary that the two images should
coincide.