196 R. Clausius on the Application of the 
stant temperature of the condenser be called 7,. During the con- 
nection of the cylinder with the condenser, the piston goes back 
again through the whole space which it previously passed over, 
and thereby all the steam which did not of itself pass directl 
into the condenser is driven into this and is here condensed. It 
only remains in order to complete the cyclus of operations, to 
bring back into the boiler the liquid which has arisen from the 
condensation of the steam. ‘This purpose is served by the small 
ump D, whose action is so regulated that during the ascent of 
the piston, it draws up exactly as much liquid from the conden- 
ser as has been brought into this last by the condensation of the 
steam; and this quantity of liquid is then forced into the boiler 
by the descent of the piston. When this has here become heated 
again to the temperature 7',, everything is again in the initial 
condition, and the same series of processes can begin anew. We 
have here then to deal with a complete circular process. 
n common steam engines, the steam passes into the cylinder 
not only from one side, but alternately from both. This however 
produces only the difference that during an ascent and descent 
of the piston, two circular processes take place instead of one, 
and it is sufficient in this case also to determine the work for one 
of them in order to be able to deduce the whole work which is 
done during any time. 
19, In this determination we will, as is customary, consider the 
cylinder as a shell which is impenetrable to heat, neglecting the 
exchange of heat which takes place during one stroke between 
the walls of the cylinder and the steam. The mass in the cylin- 
not pass into the overheated condition during the expansion 
in fine drops, and sare ae can rapidly participate in the — 
Ww 
changes of bie i pea ich the steam undergoes during the 
expansion, we shall make no sensible error if we consider in cal- 
culation the temperature of the whole mass in the cylinder as _ 
he same for every determined instant of time. 
Furthermore, not to make the formulas too complicated at th 
outset, we will in the first place determine the whole work which 
is done by the pressure of the steam without taking into account 
