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 ...

SAVERY AND NEWCOMEN 59
of the atmosphere, will vaporize at a very low temperature,
(17); and it was found that a vapour possessing a considerable elasticity would, notwithstanding the condensation,
remain in the vessels v v' and the pipe s, and would oppose
the ascent of the water. In consequence of this, it was
found that the engine could never be placed with practical
advantage at a greater height than 26 feet above the level of
the water to be raised.
(34.) When the water is elevated to the engine, and the
steam vessels filled, if steam be introduced above the water
in v, it must first balance the atmospheric pressure, before
it can force the water through the valve B. Here, then,
is a mechanical pressure of 15lbs. per square inch expended, without any water being raised by it. If steam
of twice that elastic force be used, it will elevate a column
in F of 34 feet in height; and if steam of triple the force
be used, it will raise a column of 68 feet high, which, added
to 26 feet raised by the atmosphere, gives a total lift of 94
feet.
In effecting this, steam of a pressure equal to three times
that of the atmosphere acts on the inner surface of the
vessels v v'. One third of this bursting of the pressure is
balanced by the pressure of the atmosphere on the external
surface of the vessels; but an effective pressure of 301bs. per
square inch still remains, tending to burst the vessels. It
was found that the apparatus could not be constructed to
bear more than this with safety; and, therefore, in practice,
the lift of such an engine was limited to about 90 perpendicular feet. In order to raise the water from the bottom of
the mine by these engines, therefore, it was necessary to
place one at every 90 feet of the depth; so that the water
raised by one through the first 90 feet should be received in
a reservoir, from which it was to be elevated the next 90 feet
by another, and so on.
Besides this, it was found that sufficient strength could
not be given to those engines, if constructed upon a large