LXVIII
dering that by cooling this vapour may be condensed Papin
succeeded in raising and lowering a piston in a vertical cylinder.
350. This led to the invention of the Steam-Engines. 351.
352. 354. The force of such engines depending upon the elas
tic force of the steam and the surface of the piston. 351.
Newcomen's and Cawley's engine, in which the pressure of
the atmosphere causes the piston to descend. 351, 1.
How James Watt improved it a) by the Condenser, 351,
2, a cylinder, in which the steam is cooled to prevent the cooling
of that cylinder in which the piston moves.
b) The valve-chest, an arrangement, by which the steam
is caused to pass alternately above and below the piston.
(See No. 72.) 351, 3.
c) By means of the connecting rod and crank the
(rectilinear motion is changed into a continuous circular motion
(see No. 73) and by the Fly-wheel the dead points are over
come and regular motion is kept up. 351, 4.
d) Watt added three pumps worked by the engine itself:
the cold water pump, which replaces the heated water in the
condenser, the air (or warm-water) pump, which withdraws
from the condenser the air and water accumulating there and
the feed-pump, which forces the same water (withdrawn by the
air-pump from the condenser) to enter the boiler. 351, 5.
e) The Regulator, by which the engine itself regulates
the quantity of steam entering the valve-chest, thus keeping up
a uniform motion. 351, 6.
An application of this engine we see in the Steamers.
(Robert Fulton, Ericson and Smith 1807-1839.) 351, 7.
The Locomotive wants neither cold water-pump and air-
pump, nor the fly-wheel, being a high pressure-engine and
