Against the wall of a room, near the ceiling, fix a wheel of twelve or
eighteen inches diameter; on the rim of which place a number of bells
in tune, and, if you please, of different sizes. To the axis of this
wheel there should be fixed a fly to regulate its motion; and round
the circumference there must be wound a rope, to the end of which is
hung a weight.
Near to the wheel let a stand be fixed, on whi
h is an upright piece
that holds a balance or moveable lever, on one end of which rests the
weight just mentioned; and to the other end must hang an inverted
hollow cone, or funnel, the aperture of which is very small. This cone
must be graduated on the inside, that the sand put in may answer to
the number of hours it is to run. Against the upright piece, on the
side next the cone, there must be fixed a check, to prevent it from
descending. This stand, together with the wheel, may be enclosed in a
case, and so contrived, as to be moved from one room to another with
very little trouble.
It is evident, from the construction of this machine, that when a
certain quantity of the sand is run out, the weight will descend, and
put the wheel in motion, which motion will continue till the weight
comes to the ground. If the wheel be required to continue longer in
motion, two or more pulleys may be added, over which the rope may run.