th
the spindle of the governor, as the rotation of the balls is less or more
rapid, the eccentricity of the cam determining the amount of steam admitted
to the working cylinder of the engine. To produce this effect the cam is
made as follows:

_C_ is a hollow cylinder or shell, with a part of one end formed into a cam
proper. Throughout the whole length of this piece, upon the inside, there
is a spiral groove cut to receive one end of a feather, by which its pitch
or eccentricity is regulated. _C'_ is also a hollow cylinder or shell, of
the same length and diameter as _C_, with a similar spiral groove cut on
the inside, the outside being perfectly smooth and plain, upon which the
toe (_t_) for closing the valves is fastened. The inside piece consists of
two hubs _D, D'_, eccentric with each other, and made in one piece, _D_
being turned to exactly fit the inside of the shell _C_, and _D'_ to fit
the shell _C'_, the hub _D'_ having a socket (_c_) into which the spindle
(_s_) of the governor is screwed; the end (_d_) of the hub _D_ forming a
journal or bearing, with a bevel wheel on its extremity to convey motion
from the crank-shaft gearing to the governor and cut-off. There is a hole
throughout the length of the inside hubs _D_ and _D'_, which is continued
through the spindle of the governor, and contains the rod (_r_) that
connects the cam with the governor. This hole is eccentric to the outside
surface of the hub _D_, as well as to the shell _C_, and concentric with
the hub _D'_ and shell _C'_, and with the governor rod (_r_).

The shell _C_ and hub _D_, and shell _C'_ and hub _D'_, are connected
together by feathers; one piece of each feather is of a spiral form, and
the other a straight or rectangular piece, the two being connected together
by a stub on the rectangular piece, which fits into a hole or bearing in
the other or spiral piece, so that the latter can turn on the stub and
accommodate itself to the groove in which it has to work. The spiral part
of each feather works in the spiral groove on the inside of its
corresponding shell _C_ and _C'_ respectively, and the rectangular pieces
work in a straight groove cut in the hubs _D_ and _D'_, the inner parts of
the rectangular pieces being fastened to the governor rod (_r_), so that
the feathers are permanently connected with the governor.

The shell _C'_ revolves inside of two yokes (_y_) and (_y'_), one attached
to each steam-valve toe, (_a_) and (_a'_) respect