LOCOMOTIVE ENGINE. 443 



are carried on towards the smoke box; and when the axle si revolves, the eccentric 

 B C revolving with it, turns round inside of the brass ring H H, which is prevented 

 from revolving by the eccentric rod that is fixed to it. The groove of the eccentric and 

 the brass ring are both turned exactly to fit, allowing the eccentric to turn freely and 

 steadily within the ring. As the eccentric projects from the axle more on one side 

 than the other, the ring is pushed out farther from the axle on that side ; and hi re- 

 volving with the axle, the ring is pushed out from the axle on each side in succession, 

 causing the eccentric rod to be moved in each direction from its central position as much 

 as the projection or the eccentricity, which is an inch and a half, or three inches total 

 motion or throw. 



The action of the eccentric is precisely similar to that of a crank an inch 

 and a half long ; and the eccentric is in fact a crank with a very large crank 

 pin, this pin being ten inches in diameter, and reaching beyond the axle 

 itself; and the eccentrics are used instead of cranks, to avoid the necessity of 

 making so many small cranks in the axle, though there is considerable loss of 

 power attending the use of them from the friction being increased by their 

 large size. Eccentrics are used for working the slide valves in almost all steam 

 engines, because of their convenience and steady action ; they are also readily 

 capable of adjustment, by altering the position in which they are keyed on the axle. 

 They cannot be cast in one piece as the cranks are forged with the axle, and the ec- 

 centrics have, therefore, to be put on in two halves. 



SLIDE-VALVE GEAR. A side elevation of the eccentric rods and levers for working 

 the slides is shewn detached in figs. 2 and 3, (Plate XCI.,) in two different positions, 

 with a cross section through the eccentric rods, shewing a back elevation of the levers, 

 &c., in fig. 4 ; and a plan of them is given in Plate XCI., in their position in the en- 

 gine. The two eccentrics E' and E", are, for working the slides when the engine is 

 running forward ; E' being for the slide of the right hand cylinder, andE" for that of 

 the left cylinder, and the ends of the eccentric rods, e" e", are formed into large ver- 

 tical forks, g" g", having a notch in the bottom of each ; the section in fig. 4 (Plate 

 XCI.) is taken through the notches. These notches take hold of steel pins, with 

 shoulders to hold the eccentric rod steadily, which are fixed into the lower ends of the 

 levers h" Ji", by means of nuts screwed on at the other side. The levers h" h!" are keyed 

 on to the ends of the horizontal shafts or weigh-bars i" i'", turning in brass carriages, 

 W k'", fixed on to the frame of the engine, and made in two pieces, the upper part being 

 loose and held down upon the weigh-bar by bolts, allowing it to be tightened up as it 

 wears. Upon the weigh-bars i" i'", and standing above, are fixed the levers I" F, of the 

 same length as the bottom levers, h" Ji" ; and two horizontal links, m" m", are attached 



