But we must observe that even according to such a hypothesis,
the point, f, would not be entirely stationary, because the point
of articulation, a, upon the piston rod being obliged to follow an
invariably straight line, the slots, d, will have to undergo an
alternate sliding motion on the slides, e, save, be it understood,
when the latter are brought to coincide exactly with the center of
articulation, a. Now we shall, in fact, see that the point, f, can move
forward in following the slots, d, and that it may even reach the point
of articulation, a, of the beam, F, on the rod, E, that is to say,
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.
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