open the upper exhausting
valve E, and the lower steam valve V', and close the upper steam valve V
and the lower exhausting valve E'. On the other hand, when the handle H is
pressed up it opens the upper steam valve V and the lower exhausting valve
E', and at the same time closes the upper exhausting valve E, and the lower
steam valve V'.

99. _Q._--Where is the condenser situated?

_A._--The condenser K is immerged in a cistern of cold water. At its side
there is a tube I, for the admission of water to condense the steam, and
which is governed by a cock, by opening which to any required extent, a jet
of cold water may be made to play in the condenser. From the bottom of the
condenser a short pipe leads to the air pump J, and in this pipe there is a
flap valve, called the foot valve, opening towards the air pump. The air
pump is a pump set in the same cistern of cold water that holds the
condenser, and it is fitted with a piston or bucket worked by the rod L,
attached to the great beam, and fitted with a valve opening upwards in the
manner of a common sucking pump. The upper part of the air pump
communicates with a small cistern S, called the hot well, through a valve
opening outwards and called the delivery valve. A pump M, called the hot
water pump, lifts hot water out of the hot well to feed the boiler, and
another pump N lifts cold water from a well or other source of supply, to
maintain the supply of water to the cold water cistern, in which the
condenser and air pump are placed.

100. Q.--Will you explain now the manner in which the engine acts?

A.--The piston being supposed to be at the top of the cylinder, the handle
H will be raised by the lower pin or tappet on the air pump rod, and the
valves V and E' will be opened, and at the same time the other pair of
valves V' and E will be closed. Steam will therefore be admitted above the
piston and the steam or air which had previously filled the cylinder below
the piston will be drawn off to the condenser. It will there encounter the
jet of cold water, which is kept constantly playing there by keeping the
cock I sufficiently open. It will thus be immediately condensed or reduced
to water, and the cylinder below the piston will have a vacuum in it. The
steam therefore admitted from the steam pipe through the open valve V to
the top of the cylinder, not being resisted by pressure below, will press
the piston to the bottom of the cylinder. As it approaches that posi