occupy the position shown in Fig. 18, where the oscillation of the beam,
F, being effected according to the point, a, the stroke of the piston
has become absolutely null.

The position of the piece, H, is, in effect, variable with the pressures
that are manifested in the pump. It will be seen that the latter has a
tubular appendage, g, in whose interior there plays what is called
a "starting rod," h, which is constantly submitted to the pressures
existing in the interior of the pump, and which rests against the lower
arm, H, of the piece, H. But this latter is also loaded at the opposite
side with heavy counterpoises, i, which counterbalance, within a
determinate limit, the action of the rod, h, that tends constantly to
cause the lever, H, to oscillate around its pivot, in the brackets, c.

To sum up, then, as long as the pressure in the pump has not reached a
determinate limit, the lever, H, held by its counterpoises, _i_,
will keep the position shown in Fig. 16, and for which the center of
oscillation, f, corresponds with the maximum stroke of the pump piston.
But as soon as such limit is exceeded, the equilibrium being broken, the
action of the rod, h, predominates, the piece, H, reverses from right to
left, the point of oscillation, f, moves forward in the slots, d, and
the stroke of the piston is reduced just so much. If, finally, the
pressure continues to increase, the motion of the piece, H, will
continue, and the point of oscillation, f, will reach the position for
which the motion of the piston ceases completely (Fig. 18).

But it results further, therefrom, that if when such position is
reached, the pressure diminishes, the lever, H, will, under the
influence of its counterpoise, tend to return to its first position and
thus set the piston in motion. As we remarked in the beginning, the