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 ...

70 THE STaIM ENGINE.
resistance of this vapour, and lib. per square inch for friction
&c.; so that the effective force will be found by subtracting
these 4lbs. per square inch from the atmospheric pressure;
which, if estimated at 15lbs., leaves an effective working
power of about llbs. per square inch. This, however, is
rather above what is commonly obtained.
Another advantage which this engine has over those of
Savery, is the facility with which it might be applied to
drive machinery by means of the working beam.
The merit of this engine as an invention must be ascribed
principally to its mechanism and combinations. We find in
it no new principle; the agency of atmospheric pressure
acting against a vacuum, or a partial vacuum, was long known.
The formation of a vacuum by the condensation of steam had
been suggested by Papin and Savery, and carried into practical effect by the latter. The mechanical power derivable
from the direct pressure of the elastic force of steam was
distinctly pointed out by Lord Worcester, and even prior
to his time; the boiler, gauge pipes, and regulator of the
atmospheric engine, were evidently borrowed from Savery's
engine. The idea of working a piston in a cylinder by
the atmospheric pressure against a vacuum below, was suggested by Otto Guericke, an ingenious German philosopher,
the inventor of the air-pump, and subsequently by Papin;
and the use of a working beam could not have been unknown.
Nevertheless, considerable credit must be acknowledged to
be due to Newcomen for the judicious combination of those
scattered principles. "The mechanism contrived by him,"
says Tredgold, "produces all the difference between an
efficient and inefficient engine, and should be more highly
valued than the fortuitous discovery of a new principle."
The rapid condensation of steam by the injection of water,
the method of clearing the cylinder of air and water after the
stroke, are,wo contrivances not before in use, and which are
quite essential to the effective operation of the engine: these
ge whtollv due to Newcomen and his associates.
(44.) The patent of Newecomen was granted in 1705; and