The governor, or “fly-ball governor,” as it is
often distinctively called, was another of Watt’s minor
but very essential inventions. Two heavy iron or brass balls
(B and B) were suspended from pins (C and Ct') in a little cross-piece
carried on the head of a vertical spindle (A and A') driven by
the engine. The speed of the engine varying, that of the spindle
changed correspondingly, and the faster the balls were swung
the farther they separated. When the engine’s speed decreased,
the period of revolution of the balls was increased, and they
fell back toward the spindle. Whenever the velocity of the engine
was uniform, the balls preserved their distance from the spindle
and remained at the same height, their altitude being determined
by the relation existing between the force of gravity and centrifugal
force in the temporary position of equilibrium. The distance
from the point of suspension down to the level of the balls is
always equal to 9.78 inches divided by the square of the number
of revolutions per second, i.e. h = 9.78N.
The arms carrying the balls, or the balls themselves, are
pinned to rods (M and M') which are connected to a piece (N and
N'), sliding loosely on the spindle. A score cut in this piece
engages a lever (V) and, as the balls rise and fall, a rod is
moved, closing and opening the throttle-valve and thus adjusting
the supply of steam in such a way as to preserve a nearly fixed
speed of engine. The connection with the throttle-valve and with
the cut-off valve-gear is seen not only in the engraving of the
double-acting Watt engine, but also in those of the Greene and
the Corliss engines. This contrivance had previously been used
in regulating waterwheels and windmills. Watt’s invention
consisted in its application to the regulation of the steam-engine...
Source: A History of the Growth of the Steam-Engine, by Robert H. Thurston, A. M., C.
E., Professor of Mechanical Engineering in the Stevens Institute
of Technology, Hoboken, N. J.; Member of the Institution of Engineers
and Shipbuilders of Scotland, Associate British Institution of
Naval Architects, etc., etc.; Published; New York: D. Appleton
and Company, 549 and 551 Broadway. 1878.
