, average thickness 13 ft., was embedded in the
ground to a depth of about 7 ft. A single hole 8 ft. deep was charged
with 20 oz. 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.
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