ddle of the picture, from the forcing-pump to the great
cylinders on the right hand. Here the water presses upward upon the
under surfaces of pistons working within the great cylinders, with a
force proportioned to the ratio of the area of those pistons compared
with that of one of the pistons in the pump. Now the piston in the
force-pump is about one inch in diameter. Those in the great cylinders
are about twelve inches in diameter, and as there are four of the great
cylinders the ratio is as 1 to 576.[5] This is a great multiplication,
and it is found that the force which the men can exert upon the piston
within the small cylinder, by the aid of the long lever with which they
work it, is so great, that when multiplied by 576, as it is by being
expanded over the surface of the large pistons, an upward pressure
results of about eight hundred tons. This is a force ten times as great
in _intensity_ as that exerted by steam in the most powerful sea-going
engines. It would be sufficient to lift a block of granite five or six
feet square at the base, and as high as the Bunker Hill Monument.

Superior, however, as this force is, in one point of view, to that of
steam, it is very inferior to it in other respects. It is great, so to
speak, in _intensity_, but it is very small in _extent_ and _amount_. It
is capable indeed of lifting a very great weight, but it can raise it
only an exceedingly little way. Were the force of such an engine to be
brought into action beneath such a block of granite as we have
described, the enormous burden would rise, but it would rise by a motion
almost inconceivably slow, and after going up perhaps as high as the
thickness of a sheet of paper, the force would be spent, and no further
effect would be produced without a new exertion of the motive power. In
other words, the whole amount of the force of a hydraulic engine, vastly
concentrated as it is, and irresistible, within the narrow limits within
which it works, is but the force of four or five men after all; while
the power of the engines of a Collins' steamer is equal to that of four
or five thousand men. The steam-engine can do an _abundance_ of _great_
work; while, on the other hand, what the hydraulic press can do is very
little in _amount_, and only great in view of its extremely concentrated
intensity.

Hydraulic presses are consequently very often used, in such cases and
for such purposes as require a great force within very narrow limits