186 OF THE CONSTRUCTION OF [SECT. vi. 



it is never less than the force of the steam on the smaller piston. This arrange- 

 ment was devised by Hornblower. (Art. 32.)' The engines may be of either single 

 or double power ; but whether the engine has double or single power, it is, in the 

 usual construction, a complex piece of machinery. 



391. We may now proceed to arrange the different species, and show the 

 proportions adapted to particular cases. 



CONDENSING STEAM ENGINES. 



fl. Atmospheric pressure Newcomen, 1705. 



I. By condensation ( 2 . Steam pressure (Single Watt, 1769. 



I Double Watt, 1782. 



{1. Atmospheric pressure 



f Single Watt, 1782. 



2. Steam pressure < Double Watt, 1782. 



Combined cylinder Hornblower, 1781. 



III. By generation and condensation. 



Cornish engines on Watt's construction, 

 omgie i 

 insion, J 



and condensation 



IV. By generation, expansion, f Dg " I Woolf, 1804. 



I D hi / Cornish engines on Watt's construction. 

 ' I Woolf, 1804. 



OF THE CONSTRUCTION OF ENGINES WORKING BY CONDENSATION. 



392. Of the engines working by condensation alone, two kinds may be 

 distinguished ; in the one kind the moving force is the pressure of the atmosphere, 

 in the other it is the pressure of steam : the former may be further divided into 

 those which condense in the cylinder, and those having separate condensers ; and 

 the latter into single and double acting engines. 



ATMOSPHERIC ENGINES. 



393. The common atmospheric engine. In the atmospheric engine, as it is 

 usually constructed, condensation is effected in the cylinder. The parts required 

 for this object are, a cylinder C, Plate vi. Figs. 1 and 2. close at the bottom and 

 open at the top ; a piston P ; a passage S for the steam from the boiler to the 

 bottom of the cylinder, provided with a valve V, or cock ; a passage for cold water 

 to condense the steam, to inject into the cylinder at I, with a cock D ; and a 



