382 EXPLANATION OF THE PLATES. 



ing on their axes C', transmit the motion to the connecting rod G, through its side 

 links or forks H, and fork head F. 



The crank I, being impelled by the upper end of the connecting rod, produces a 

 rotary motion about the paddle shaft N, which is supported by the framing K K. 



The air-pump bucket M', receives its motion through the cross head P and side 

 rods Q, which are connected to the beams at Q'. 



To maintain rectilinear motion of the piston rod, a perpendicular rod 27, from the 

 beam C, is caused to act on the radius crank 28, and parallel rods 29, whose action 

 is transmitted to the piston through the side rods E, as in the other parallel motions. 



PLATES LI., LII., LIIL, AND LIV. 



ENGINES OF THE HULL AND LONDON PACKET WILLIAM WILBERFORCE. 



Plate LI. represents a plan of the engines of the Wilberforce Hull and London 

 packet, built by John and Edward Hall, of Dartford, and fitted with Samuel Hall's 

 patent condensers, and Francis Humphrys's patent slides. The mechanical ar- 

 rangement of these engines differ from other marine engines provided with Hall's 

 condensers, as every part of the condensing apparatus is fixed on the foundation 

 plates of the engines, and the cold water pumps receive their motion directly from 

 the great levers, by means of side rods and cross heads, like the air pumps, by which 

 arrangement the parallelism of the several rods employed in working the cold water 

 pumps is preserved, and the pumps themselves firmly and substantially fixed and 

 united with the several other parts comprising the engines ; thus also affording every 

 convenience for ready access to the valves or plungers in case of their requiring re- 

 pairs. 



The slide valves of these engines, as well as the pistons and air pump buckets, are 

 wholly metallic, and their operation have proved them to be quite as efficient as D 

 slide valves in their most perfect condition without requiring any care or attention 

 from the engineer ; and they work with so little friction that one man can when re- 

 quired handle both engines, although the leverage power, as will be seen by inspect- 

 ing the engravings, is little more than as two to one ; this affords a great advantage 

 to a marine engine, particularly in a crowded river like the Thames, through which 

 the Wilberforce has to pass ; but their more important advantage is felt in the 

 steady maintenance of the power of the engines, and in the economy of fuel arising 

 from the total absence of the leakage common to all hemp packed slide valves when 

 neglected by the engine man or not plentifully supplied with melted tallow. 



