LOCOMOTIVE ENGINE. 
447 
slides and levers being moved to the right position by means of two starting handles 
fixed on to the fire-box, and connected by rods and levers with the two weigh- 
bars, and these starting levers are always moving with the slides. This plan 
is inferior to the other with the forked eccentric rods, as the slides have to be 
set by the starting handles, as well as the eccentrics reversed, in order to reverse the 
engine; though when the engine is running, the first is not required, but a con 
siderable strain is then caused by the eccentric rods suddenly catching hold of the pins 
and bringing them into motion. The starting handles are used to enable the engine 
to be moved very steadily or for a small distance by working the slides by hand, 
the eccentrics being thrown out of gear; but a good regulator renders them un 
necessary for this purpose, as the steam can be admitted very gradually to the 
cylinders. Considerable friction is also caused by their being continually in motion 
with the slides, and to avoid this, another handle has been added in some cases, 
by means of which they can be thrown out of gear when not required; but that 
adds to the complexity. 
The plan of driving the slides that has hitherto been most universally adopted, 
and is still much used, is by means of two eccentrics only, fixed together at right 
angles to each other, and placed loose upon the centre of the cranked axle; their 
rods being connected with the weigh-bars, as in the other plans ; and a driver with a 
projecting stud is fixed on the axle on each side, just clearing the eccentrics, a hole 
being made in each side of the eccentrics to fit the studs. The eccentrics can be 
shifted along the axle to either side by means of a lever, to make the stud in the 
driver on that side drop into the hole in the eccentric when it comes opposite to it 
in revolving, and cause the eccentric to turn with the axle and work the slides. 
The stud of the other driver is put on the opposite side of the axle to the corre 
sponding hole in the eccentric; so that when the eccentrics are shifted to the other 
side by the lever, they have to stop for half a revolution before that driver catches 
hold of them, and are then fixed exactly opposite to their former position, and 
reverse the engine; in their intermediate position, when they touch neither of the 
drivers, they are stationary and cease to work the slides. This plan is inferior to 
those with four eccentrics, as it is not so certain in its action, and does not keep in 
order so well. 
Working of Slides and Piston.—As the slides are worked by eccentrics, they 
are not suddenly reversed in position at the end of each stroke, in order to let the 
steam on to the other side of the piston, and keep the steam port full open, 
throughout the stroke; but are always in motion, and commence returning as soon 
as they have arrived at the end of their stroke. From this cause they are obliged