334 
Steafn Engine. 
steam below the piston, Mr. W. introduces below it, and 
into the receiver, such a quantity of oil. See. as shall, when 
the piston is at its greatest height, in the working cylin= 
der, fill all the space below it, and fill also the receiver up 
to the height of a few inches above the lower rim of the 
working cylmder. If the engine is to be worked by the 
pressure of the atmosphere, the receiver has a communi- 
cation with the boiler, which communication being open- 
ed, steam is admitted into, and fills the receiver above the 
oil. If the communication between the receiver and the 
boiler be now shut olF, and a communication be opened 
from the receiver to the condenser, a vacuum will be 
formed in the receiver, and then the pressure of the at- 
mosphere, acting upon the piston, will cause it to descend 
in the working cylinder, pressing the oil, or other fluid 
body, before it, and causing the fluid to ascend into the 
receiver ; after which the steam is again admitted for the 
next stroke* If the engine is to be worked by the action 
of the steam upon the piston, then the working cylinder 
must, as is usual in steam engines so worked, be furnish- 
ed with a cover. In this case, instead of the communica- 
tion usual in the engines in common use, for the alternate 
admission and condensation of steam above and below 
the -piston, the communications in this engine are to the 
upper part of the working cylinder, and to the upper part 
of the receivers, the receiver in the engine answering to j 
the space below the piston in other steam engines ; so 
that, v/hen the receiver is open to the condenser, and 
the upper part of the working cylinder open to the boiler, 
the piston ascends, and vice versa* To prevent waste of ' 
steam, and to keep up the temperature of the oil, the re- 
ceiver may be enclosed in a steam case, or heat may be ! 
applied externally. There should always be some oil 
above the piston to the height of a few inches, to prevent 
the passage of the atmospheric air, or of the ^steam, down ^ j : 
