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Mechanical Theory of Heat to the Steam Engine. 188 
nally filled with liquid ether and is then completely pumped _ 
back into the boiler. In like manner the ether vapor is con- 
to keep up a uniform action, therefore, it is only necessary to 
add as much water or ether as escapes through the joints from 
imperfections in the construction 
6. In a machine of this kind in which the same mass is always 
This is the case with steam engines with condensers, in which 
the water is thrown out from the condenser in the liquid state, 
and with the same temperature with which it passed from the 
condenser into the boiler.* 
_ In other machines the condition at the exit is different from 
that at the entrance. The caloric air machines, for instance, even 
when they are provided with regenerators, force the air into the 
atmosphere with a. higher temperature than it previously had, 
and the steam engines without condensers take up the water asa 
be completed for the purpose of investigation, we aa apply to 
all thermo-dynamic machines the theorems which hol 
* The cooling water which passes into the condenser cold and out of it warm, 
is not hove: takes into consideration, since it does not belong to the heat-utilizing 
substance, but serves only as a negative source of heat. 
