116 
Steam Engine* 
ton e arrives at the bottom of the cylinder, a valve which 
is in the piston, is opened by its pressing against the bot- 
tom, and opens a communication with the condenser, 
whilst the spring k, fixed to the rod of the piston, shuts 
the valve which admits the steam from the boiler. The 
steam, therefore, being thus condensed, runs into the 
lower pipe f. The piston e, arriving at the bottom of the 
pipe in which it works at the same time with c, presses 
upon the condensed water, shuts the valve f, and forces 
the water up the pipe g, into the box h. The air which 
is disengaged from the water, rises to the top of the box, 
and, by its elasticity, forces the water through the pipe i, 
which carries it back again into the boiler. When the 
air accumulates in the box to such a degree as to depress 
the water, the ball-cock falls with it, and opens a valve 
in the top of the box, which suffers some of the air to es- 
cape. 
When all the steam is condensed, the motion of the fly 
attached to the machine brings the piston up again, its 
valve now remaining shut by its weight. On arriving at 
the top, it presses up the steam-valve, which admits the 
steam from the boiler to force it down as before. 
1 and m are two cranks, upon whose axis are two equal 
wheels working in each other, for the purpose of convert- 
ing the perpendicular motion of the piston-rod into a rota- 
tory motion, for working the machinery attached to it. 
But the most valuable part of this engine is in the con- 
struction of the piston, 'which Mr. Cartwright made whol- 
ly of metal, and so as by means of springs, to fit the cy- 
linder very exactly. This not only saves the expence 
and trouble of packing, which they are obliged frequent- 
ly to renew in all other engines, but also saves a great deal 
of steam, on account of the more accurate fitting of the 
piston. 
