eam, cold water
was poured over its outside surface, creating a vacuum through
condensation and causing it to fill again while the water in the other
reservoir was being forced out. A number of machines were built on this
principle and placed in actual use as mine pumps.

The serious difficulty encountered in the use of Savery's engine was the
fact that the height to which it could lift water was limited by the
pressure the boiler and vessels could bear. Before Savery's engine was
entirely displaced by its successor, Newcomen's, it was considerably
improved by Desaguliers, who applied the Papin safety valve to the
boiler and substituted condensation by a jet within the vessel for
Savery's surface condensation.

In 1690, Papin suggested that the condensation of steam should be
employed to make a vacuum beneath a cylinder which had previously been
raised by the expansion of steam. This was the earliest cylinder and
piston steam engine and his plan took practical shape in Newcomen's
atmospheric engine. Papin's first engine was unworkable owing to the
fact that he used the same vessel for both boiler and cylinder. A small
quantity of water was placed in the bottom of the vessel and heat was
applied. When steam formed and raised the piston, the heat was withdrawn
and the piston did work on its down stroke under pressure of the
atmosphere. After hearing of Savery's engine, Papin developed an
improved form. Papin's engine of 1705 consisted of a displacement
chamber in which a floating diaphragm or piston on top of the water kept
the steam and water from direct contact. The water delivered by the
downward movement of the piston under pressure, to a closed tank, flowed
in a continuous stream against the vanes of a water wheel. When the
steam in the displacement chamber had expanded, it was exhausted to the
atmosphere through a valve instead of being condensed. The engine was,
in fact, a non-condensing, single action steam pump with the steam and
pump cylinders in one. A curious feature of this engine was a heater
placed in the diaphragm. This was a mass of heated metal for the purpose
of keeping the steam dry or preventing condensation during expansion.
This device might be called the first superheater.

Among the various inventions attributed to Papin was a boiler with an
internal fire box, the earliest record of such construction.

While Papin had neglected his earlier suggestion of a steam and piston
engine to work on Sav