ery's ideas, Thomas Newcomen, with his assistant,
John Cawley, put into practical form Papin's suggestion of 1690. Steam
admitted from the boiler to a cylinder raised a piston by its expansion,
assisted by a counter-weight on the other end of a beam actuated by the
piston. The steam valve was then shut and the steam condensed by a jet
of cold water. The piston was then forced downward by atmospheric
pressure and did work on the pump. The condensed water in the cylinder
was expelled through an escapement valve by the next entry of steam.
This engine used steam having pressure but little, if any, above that of
the atmosphere.

[Illustration: Two Units of 8128 Horse Power of Babcock & Wilcox Boilers
and Superheaters at the Fisk Street Station of the Commonwealth Edison
Co., Chicago, Ill., 50,400 Horse Power being Installed in this Station.
The Commonwealth Edison Co. Operates in its Various Stations a Total of
86,000 Horse Power of Babcock & Wilcox Boilers, all Fitted with Babcock
& Wilcox Superheaters and Equipped with Babcock & Wilcox Chain Grate
Stokers]

In 1711, this engine was introduced into mines for pumping purposes.
Whether its action was originally automatic or whether dependent upon
the hand operation of the valves is a question of doubt. The story
commonly believed is that a boy, Humphrey Potter, in 1713, whose duty it
was to open and shut such valves of an engine he attended, by suitable
cords and catches attached to the beam, caused the engine to
automatically manipulate these valves. This device was simplified in
1718 by Henry Beighton, who suspended from the bottom, a rod called the
plug-tree, which actuated the valve by tappets. By 1725, this engine was
in common use in the collieries and was changed but little for a matter
of sixty or seventy years. Compared with Savery's engine, from the
aspect of a pumping engine, Newcomen's was a distinct advance, in that
the pressure in the pumps was in no manner dependent upon the steam
pressure. In common with Savery's engine, the losses from the alternate
heating and cooling of the steam cylinder were enormous. Though
obviously this engine might have been modified to serve many purposes,
its use seems to have been limited almost entirely to the pumping of
water.

The rivalry between Savery and Papin appears to have stimulated
attention to the question of fuel saving. Dr. John Allen, in 1730,
called attention to the fact that owing to the short length of time of