444 TRANS. ST. LOUIS ACAD. SCIENCE. 



represent brake horse-power as a function of boiler pressure. 

 The discussion then becomes more complex, although it can be 

 made on the lines here laid down. It is better to avoid this 

 discussion by refraining from building such engines. 



The experience of the writer with condensing-engines has been 

 very limited, but it would appear that the equations here given 

 will apply also to them. 



The four surfaces here discussed may all be constructed by 

 means of threads to represent the two sets of rectilinear elements 

 in each. These are constant speed, and constant load. Such 

 models represent the working conditions of an engine in a most 

 interesting way. 



