The steam engine familiarly explained and illustrated; with an historical sketch of its invention and progressive improvement; its applications to navigation and railways; with plain maxims for railway speculators. By the Rev. Dionysius Lardner ... With additions and notes by James Renwick ...

DOUBLE-ACTING- STEAM ENGINE. 107
consists its whole efficacy as a regulator. Its regulating
power is limited, and it is only small changes of velocity
that it will correct. It is evident that such a velocity as, on
the one hand, would cause the balls to fly to the extremity
of their play, or, on the other, would cause them to fall down
on their rests, would not be influenced by the governor.
We have thus described the principal parts of the doubleacting steam engine. The valves and the methods of working them have been reserved for the next chapter, as they
admit of considerable variety, and will be better treated of
separately. We have also reserved the consideration of the
boiler, which is far from being the least interesting part of
the modern steam engine, for a future chapter.
arcs be unequal, are equal in time, provided those arcs be small, so also is the
periodic time of the revolving ball invariable. These observations, however,
only apply when the balls settle themselves steadily into a circular motion; for
while they are ascending they describe a spiral curve with double curvature,
and the period will vary. This takes place during the momentary changes in
the velocity of the engine.