112 
Steam JEngine, 
and water from the condenser : it is worked by the great 
beam or lever ; and the water brought by it from the con- 
denser, after being brought into the hot-well g, is pumped 
up again by the pump h, and is brought back again into 
the boiler by the pipe i. k is another pump, also worked 
by the engine itself, which supplies the cistern in which 
the condenser is placed, with cold water. 
In the old engines, where the working stroke was only 
downwards, the piston-rod was attached to the beam by 
chains, which bent round an arch on the end of the beam, 
in order to make the piston-rod move always in a perpen- 
dicular direction. This may be seen in the plate of New- 
comen’s engine. But in Mr. Watt’s engines, where the 
working-stroke is doubled, that is, both upwards and 
downwards, chains could not answer this purpose, as, 
when the piston was forced upwards, they would slacken, 
and would not communicate the motion to the beam. It 
was necessary, therefore, that the piston-rod should be fas- 
tened to the beam by inflexible bars ; but that the stroke 
might be perpendicular, a particular contrivance was 
invented by Mr. Watt, which is exhibited in the plate, 
and which answers the intended purpose admirably. It 
is usually called the parallel joint, and its nature and con- 
struction will be easily understood from the figure. In 
order to make the engine itself open and shut the steam 
and eduction- valves, long levers are attached to them, 
which are moved by the piston-rod of the air-pump E F. 
This part of the apparatus is called the working-geer, and 
is so contrived, that the valves may be worked either by 
hand or by the perpendicular rod. By shutting these 
valves, the engine may be stopped in an instant. 
In order to communicate a rotatory motion to any ma- 
chinery by the motion of the beam of the steam-engine, 
Mr. Watt makes use of a very large fly-vrheel G; on the 
axis of which is a small concentric toothed wheel, H, A 
