181 
Steam Engine, 
from the boiler, to act by its elastic force on one side of 
the smaller piston, while the steam which had last mov- 
ed it has a communication with the larger steam vessel 
or cylinder, where it follows the larger piston, noAV mov- 
ing towards that end of its cylinder which is open to the 
condensing vessel. Let both pistons end their stroke at 
one time, and let us now suppose them both at the top of 
their respective cylinders, ready to descend ; then the 
steam of forty pounds the square inch entering above the 
smaller piston will carry it downwards, Avhile the steam 
beloAV it, instead of being allowed to escape into the at- 
mosphere, or applied to any other purpose, will pass into 
the larger cylinder above its piston, which Avill take its 
downward stroke at the same time that the piston of the 
smaller cylinder is doing the same thing ; and while this 
goes on, the steam Avhich last filled the larger cylinder in 
the upward stroke of the engine vvfli be passed into the 
condenser, to be condensed during the downward stroke. 
When the pistons in the smaller and larger cylinder have 
thus been made to descend to the bottom of their respec- 
tive cylinders, then the steam from the boiler is to be shut 
off from the top, and admitted to the bottom of the small- 
er cylinder, and the communication between the bottom 
of the smaller and the top of the larger cylinder is also to 
be cut off, and the communication to be opened between 
the top of the smaller and the bottom of the larger cylin- 
der; the steam, which in the downward stroke of the en- 
gine filled the larger cylinder, being now open to the con- 
denser, and the communication between the bottom of 
the larger cylinder and the condenser shut off ; and so al- 
ternately admitting the steam to the different sides of the 
smaller piston, while the steam last admitted into the 
smaller cylinder passes alternately to the different sides of 
the larger piston in the larger cylinder, the top and bot- 
tom of which are made to commuiiicate alternately with 
