General Description. 135
attendant can at any time regulate the speed ofthe engine.
The governor or double pendulum, is also em-ployed for this purpose. This consists of twoballs, suspended by joints projecting from a ver-tical axis, which being caused to revolve by themachine to which it is connected, will increasethe diameter of the path described by the ballswith the increasing speed of the machine ; or, inother words, their centrifugal force will causethem to fly off from the arbor in a degree pro-portionate to the velocity of the machine; andthis motion is made to actuate the lever con-nected with the valve, which admits the steamfrom the boiler to the cylinder.
Another method, is to have the small pumpworked by the engine, and raising up water intoa cistern, from which it runs out again in a con-stant stream. By this means the water will ac-cumulate, and rise in the cistern, if the enginewofk rapidly, so as to pump more water into thecistern than will flow out of it in the same time;and, on the contrary, the surface of the water willsink in the cistern, if the engine work slowly,and a float being in the cistern, and connectedwith a wire to the throttle-valve, a proportionateeffect will be produced on the engine.*