of powder and the rock was split in a straight line from
end to end and entirely to the bottom. A ledge of sandstone open on
its face and two ends, 110 x 13 x 8 ft., was moved by a blast about 3
in. without wasting a particle of rock, 8 holes being used, drilled by
three men in just one day, and 15 oz. of powder being used in each
hole. A sandstone ledge, open on the face and end only, 200 x 28 x 15
ft., containing 84,000 cu. ft. stone, was moved 1/2 in. by 25 holes,
each containing 1 lb. of powder.

* * * * *

THE TROTTER CURVE RANGER.

This little instrument was exhibited in a somewhat crude state at the
meeting of the British Association at Newcastle in 1889. It has since
been modified in several respects, and improvements suggested by
practical use have been introduced, bringing it into a practical form,
and enabling a much greater accuracy to be attained. 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. 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 m