VARIOUS MECHANICAL APPLIANCES.
derricks are used in hydraulic mines to facilitate the removal of large
boulders and rocks, which are of frequent occurrence. The present style
of bed-rock derrick has a mast ioo feet high, and a boom 92 feet long,
which is set in a cast-iron box placed on sills. The mast is held in
position by six guys of galvanized iron wire rope one inch in diameter.
A whip block, with three-quarter inch diameter steel rope, is used for
the hoisting tackle. A twelve-feet diameter Hurdy-gurdy wheel is
attached, and, using 30 inches of water under 275 feet head, it lifts
stones weighing eleven tons. The guys are held by double capstans.
This derrick can be readily moved 100 feet in ten hours without being taken down.
and electric-light machines necessitate the employment of a motor,
particularly one driven by water, and capable of utilizing high heads.
Hence the use of water-wheels of the class known as "Impact* Wheels,"
locally called " Hurdy-gurdys."
are wheels moved by a stream or jet of water issuing under pressure
from a conical nozzle and striking open buckets on the circumference of
the wheel. The buckets, originally flat, have been modified in shape,
and thereby the efficiency of the wheel greatly increased.
Experiments at North Bloomfleld.—The first
* See comment on the use of this term, p. 194. 185