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 ...

'76 THE STEAM ENGINE.
municated it to Dr. Black, who then explained to Watt his
doctrine of latent iheat, which he had been teaching for a
short time before that, but of which Watt had not previously
heard; and thus, says Watt, 1" I stumbled upon one of the
material facts on which that theory is founded."
(47.) Watt now gave his whole mind to the discovery of
a method of "' condensing the steam without cooling the
cylinder." The idea occurred to him of providing a vessel
separate from the cylinder, in which a constant vacuum
might be sustained. If a communication could be opened
between the cylinder and this vessel, the steam, by its
expansive property, would rush from the cylinder to this
vessel, where, being exposed to cold, it would be immediately condensed, the cylinder meanwhile being sustained at
the temperature of 2120~.
This happy conception formed the first step of that brilliant career which has immortalized the name of Watt, and
which has spread his fame to the very skirts of civilization.
He states, that the moment the notion of " separate condensation" struck him, all the other details of his improved
engine followed in rapid and immediate succession, so that
in the course of a day his invention was so complete that he
proceeded to submit it to experiment.
His first notion was, as we have stated, to provide a
separate vessel, called a condenser, having a pipe or tube
communicating with the cylinder. This condenser he proposed to keep cold by being immersed in a cistern of cold
water, and by providing a jet of cold water to play within
it. When the communication with the cylinder is opened,
the steam, rushing into the condenser, is immediately condensed by the jet and the cold surface. But here a difficulty
presented itself, viz. how to dispose of the condensing water,
and condensed steam, which would collect in the bottom
of the condenser. But besides this, a quantity of air or
permanent uncondensible gas would collect from various
sources. Water in its ordinary state always holds more o