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 ...

56 THE STEAM ENGINE.
force-pipe F; and this is continued until the steam has forced
all the water from v, and occupies its place.
The further admission of steam through T is once more
stopped by moving the regulator; and the condensing pipe
being again allowed to play on v, so as to condense the steam
which fills it, produces a vacuum. Into this vacuum, as
before, the atmospheric pressure on L will force the water,
and fill the vessel v. The condensing pipe being then closed
and steam admitted through T, the water in v will be forced
by its pressure through the valve B and tube E into r, and so
the process is continued.
We have not yet noticed the other steam vessel v', which,
as far as we have described, would have remained filled with
common atmospheric air, the pressure of which on the valve
A' would have prevented the water raised in the suction
pipe s from passing through it. However, this is not the
case; for, during the entire process which has been described
in v, similar effects have been produced in v', which we have
only omitted to notice, to avoid the confusion lwhDich the
two processes might produce. It will be rememberedl that
after the steam, in the first instance, having flowed from the
boiler through T, has blown the air out of v through a, the
communication between T and the boiler is closed. Now
the same motion of the regulator which closes this opens the
communication between T' and the boiler; for the slidin~g
plate n (fig. 7) is moved from the one tube to the other,
and at the same time, as we have already stated, the condensing pipe is brought to play on v. While, therefore, a
vacuum is being formed in v by condensation, the steam,
flowing through T', blows out the air through n, as already
described in the other vessel v; and, while the air in s is
rushing up through A into v, followed by the water raised
in s by the atmospheric pressure on L, the vessel v' is
being filled with steam, and the air is completely expelled
from it.
The communication between T and the boiler is now