EXPLANATION OF THE PLATES. 333 



PLATE VI. 



Fig. 1 . is a section of a common atmospheric steam engine ; C is the cylinder, 

 and the piston is supposed to have a wooden bottom, according to the practice of 

 Smeaton, (art. 466.) ; the steam is let on by a modification of Hornblower's valve, 

 (art. 442.) instead of the common regulator, (art. 461.) For the proportions of the 

 engine, see art. 393399. 



Fig. 2. is a section of an atmospheric engine with a separate condenser "and air 

 pump ; see art. 400 405. An elevation of this engine is shown in Plate xi. 



Fig. 3. is a section of a combined cylinder engine on Hornblower's principle, 

 (art. 32.) where the steam passages are opened and closed by a combination of 

 slides in one pipe. See art. 425 429. Woolf s engines have two cylinders, but 

 the passages are opened by valves. 



Fig. 4. is a section of Hornblower's double-seated valve. See art. 441. 



Fig. 5. represents a section of Murray's slide ; it is a sliding cover which alter- 

 nately covers the passages a c and c b : the disadvantage of this construction is, 

 that the pressure of the steam is nearly three times as great on the moving surfaces, 

 as it is in Murdoch's arrangement shown in the last Plate. See art. 446. 



Fig. 6. and 7. show the mode of forming the apertures of a four-passaged cock, 

 so that the steam may be shut off at any period of the stroke without closing the 

 passages to the condenser. See art. 456. T is the passage to the top, and B that 

 to the bottom of the cylinder ; the steam enters at S, and C is the passage to the 

 condenser. Fig. 6. shows the position of the cock when the steam is entering, and 

 Fig. 7. when it is shut off. 



