THE GROWTH OF THE STEAM-ENGINE. 



H7 



the steam-passages between them, permitting a symmetrical distribu- 

 tion of strain, and the use of the usual general type of beam-engine. 

 A readily-adjustable valve-gear is attached, and its cut-off gives an 

 expansion of about ten times, the boiler steam-pressure being about 

 eighty pounds per square inch. The cylinders are steam-jacketed, 

 and very thoroughly clothed with a non-conducting felting and lag- 

 ging. This engine has given the best economical results yet reported 

 in this country, attaining a " duty" on a test-trial of more than 100,- 

 000,000 pounds of water raised one foot high by each 100 pounds of 

 fuel burned. 



Still another recent form of steam pumping-engine, noted for its 

 cheapness combined with efficiency, is that of Worthington (Fig. 22), 

 in which two pairs of steam cylinders, A, _Z?, are placed side by side, 

 each pair driving a pump-plunger, JF 1 , attached to its piston-rod, and 

 each having its valve-gear, H i, M iV, actuated by the movement of 

 the piston of the other. The cylinders together form a compound 

 engine ; the steam exhausted from the smaller, A, passing into the 



.lilii'inillillr^feljS^l 



Tome of James Watt, Handswokth Church, 1819. 



larger, B, where it is further expanded. The valve-gear of this en- 

 gine is peculiarly well adapted to this type of engine. There is no 

 fly-wheel, and the motion of each of the two independent engines, 

 which together form the pair, is controlled by its neighbor, the valve- 

 gear of the one being moved by the piston of the other. This ingen- 

 ious combination permits each piston to move from end to end of its 

 cylinder, holds it stationary an instant while the pump-cylinders be- 



