come and go, look a little mysterious. Each truck
as it climbs the hill to the washing machine is
seized upon and emptied into a trough, and as its
contents are poured out, -coolies in savage-looking
rain-coats bear down on them with swift jets o f
water. Under this vigorous solvent, clay and gravel
immediately part company ; the clay to descend with
the water into a pool, whence it is hoisted away to
the river.
The gravel is now rapidly classified -by means of a
moving cylinder of graduated mesh. Through the
mesh it falls into the hands of the sorters waiting below.
But to lessen their labours, there is now in use an-
intermediate machine, the most interesting of those at
work, and known as the pulsator. It offers a simple
but interesting illustration of the 'application of fundamental
laws of nature to human use. Of all the stones
that enter the cylinder of mesh, the ruby is of the
greatest specific gravity, and all light stones can be
safely ignored. The pulsator separates the light stones
from the heavy ones. It is an iron bucket, with a
small aperture at the bottom, in which a piston moves
up and down. Water pours into the bucket, and as the
valve of the piston lifts, it rushes through this aperture,,
taking with it the heavier stones which by the constant
churning of the piston and the sucking action of the
water have gradually sunk to the bottom. The piston
is hidden from sight in the mass of gravel, and its
movement makes thej gravel pulse as if it were alive
The sucking of the water can be felt by placing one’s
806 I
From a painting by J. B. Middleton..