order that by this movement the dust, fine and coarse sand, small stones, and
fine broken rock may fall through the bottom. Others do not use a sieve, but
an open box, whose bottom is hkewise covered with wire netting ; this they
fix on a small cross-beam fastened to two upright beams and tilt it backward
and forward.
Some use a sieve made of copper, having square copper handles on both
sides, and through these handles runs a pole, of which one end projects threequarters of a foot beyond one handle ; the workman then places that end in
a rope which is suspended from a beam, and rapidly shakes the pole alter-
