LOCOMOTIVE ENGINE. 
443 
are carried on towards the smoke box; and when the axle A 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 in 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, if' 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" by means of nuts screwed on at the other side. The levers h" K" are keyed 
on to the ends of the horizontal shafts or weigh-bars i" iturning in brass carriages, 
V //', 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 T l'", of the 
same length as the bottom levers, li 1 Ji"; and two horizontal links, m m", are attached