VARIOUS MECHANICAL APPLIANCES. 203
being turned conical 12 degrees, will have a depth of 1-7/8 inches from centre to surface. The thickness may be 3/8 of an inch. The outer edge, perpendicular to axis, will require wood 2-1/4, inches thick for its construction. The best wood is Honduras mahogany." *
THE ROCKER.
The
rocker is a box 40 inches long, 16 inches wide on the bottom, 1 foot
high, with sides sloped like a cradle, and with rockers at the middle
and back end.
The
upper end is a hopper, 20 inches square, 4 inches deep, with a
perforated iron bottom with half-inch-diameter holes. This top hopper
is removable. Under the perforated plate there is a light frame,
placed on an incline, upon which a canvas apron is stretched, forming a
riffle.
In washing with the rocker the material is thrown into the hopper and water is poured on with a dipper held in
