SECT. I.] 



THE STEAM ENGINE. 



35 



of metal, and expansive : by this method he further expected some advantage from 

 saving of time and expense in the packing, and from the piston fitting more accu- 

 rately, if possible, the more it was worked. (See Sect, vn.) Cartwright was very 

 desirous of simplifying all the other parts of his engine, having only two valves, 

 and those are as nearly self-acting as may be. Cartwright's engine is represented 

 in the annexed figure. It is a single acting engine, and A is the cylinder ; B, the 

 piston ; I, the pipe which conducts the steam to C, the condenser, which is a 

 double cylinder ; the steam passes between the inner and outer one into the pump 

 D, which returns the condensed fluid back into the boiler, through E, the air box, 

 with e its valve. 



As the pipe from the pump, through which the condensed fluid is returned into 

 the boiler, passes through the air box, what air or elastic vapour may be mixed 

 with the fluid rises in the box, till the ball which keeps the valve e shut, falls and 

 suffers it to escape. 



FIG. 9. 



F is the steam valve ; a the piston valve ; H, H, two cranks, upon whose axles 

 are two equal wheels working in each other, for the purpose of giving a rectilinear 

 direction to the piston rod ; and M is the cistern that contains the condensing 

 water. The metallic pistons he formed of metal rings, as shown by the section of 



