[Illustration: Fig 1.]

I would propose the construction given in the subjoined sketch, viz.: The
drum, A (Figs. 1 and 3), is mounted in a yoke suspended in such a manner
as to bring no unnecessary, but still sufficient, pressure on the friction
roller, B, to cause it to revolve the friction cone, C (both cone and
roller being of wood and, say, well rubbed with resin so as to increase
adhesion).

[Illustration: Fig 2.]

The friction roller should be movable (on a screw thread), but so arranged
that it can be fixed at any point, say by a lock nut, screw, clamp, or
other simple means. It will be evident that, by shifting the roller, a
greater or less speed of the cone can be effected, and as to the end of
the cone's axis an index hand sweeping an ordinary clock face is attached,
the speed of this index hand can be regulated to a nicety, in proportion
to that of the drum. Of course, before fixing the size and proportion of
the disk and cone, the number of revolutions of the drum in a given time
must be ascertained by experiment. For instance, the drum being found to
make 15 revolutions in 12 hours, the proportions would be:

Circumference of roller = 12 units.
Circumference of middle part of cone = 15 units.

Or, the drum making 2½ revolutions in 3 hours, equal to 9 revolutions in
12 hours:

Circumference of roller = 12 units.
Circumference of middle part of cone = 9 units.