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. 55
together with the elastic force of the air above it, balances
the atmospheric pressure on L, (7.) When this has taken
place, the water will cease to ascend.
Let us now suppose that, by shifting the regulator, the
communication is opened between T and the boiler, so that
steam flows again into v. The condensing cock G being
removed, the vessel will be again heated as before, the air
expelled, and its place filled by the steam. The condensing
pipe being again allowed to play upon the vessel v, and the
further supply of steam being stopped, a vacuum will be
produced in v, and the atmospheric pressure on L will force
the water through the valve A into the vessel v, which it
will nearly fill, a small quantity of air, however, remaining
above it.
Thus far the mechanical agency employed in elevating the
water is the atmospheric pressure; and the power of steam
is no further employed than in the production of a vacuum.
But, in order to continue the elevation of the water through
the force-pipe F, above the level of the steam vessel, it will
be necessary to use the elastic pressure of the steam. The
vessel v is now nearly filled by the water which has been
forced into it by the atmosphere. Let us suppose that, the
regulator being shifted again, the communication between
the tube T and the boiler is opened, the condensing cock
removed, and that steam flows into v. At first coming in
contact with the cold surface of the water and that of the
vessel, it is condensed; but the vessel is soon heated, and
the water formed by the condensed steam collects in a sheet
or film on the surface of the water in v, so as to form a
surface as hot as boiling water.* The steam then, being no
longer condensed, presses on the surface of the water with
its elastic force; and when that pressure becomes greater
than the atmospheric pressure, the valve B is forced open,
and the water, issuing through it, passes through E into the
e Hot water being lighter than cold, it floats on the surface.