Any slight inaccuracy can be compensated by the cone and disk device.

The drum, or cylinder, is caused to gradually revolve by a weight attached
to an endless cord passing once around the drum. The latter might be
varnished to prevent slipping. The weight should be provided with an
automatic wedge, allowing it to be slipped along the cord in an upward
direction, but preventing its descent. The weight is represented partly in
section in the engraving. This weight should not be quite sufficient to
revolve the drum, it being counterbalanced by the liquid raised in the
chambers of the drum. The liquid, however, following its tendency to seek
the lowest level, gradually runs back through the small hole, D, in the
partitions, but is continually raised again, with the chamber it has just
entered, by the weight slightly turning the cylinder as it (the weight)
gradually gains advantage over the as gradually diminishing weight of each
chamber raised.

As to the drum, the same might be constructed as follows, viz.: First
solder the partitions into the cylinder, making them slanting or having
the direction of chords of a circle (see Fig. 2). The end disks should be
dish shaped, as shown. Place them on a level surface, apply heat, and melt
some mastic or good sealing wax in the same. Then adjust the cylinder
part, with its partitions, allowing it to sink into the slight depth of
molten matter. In this way, or perhaps by employing a solution of rubber
instead of the sealing wax, the chambers will be well isolated and not
liable to leak. The water is then introduced through the center openings
of the disks before hermetically sealing the drum to its axis.

[Illustration: Fig. 3.]