LOCOMOTIVE ENGINE. 
417 
and the exit of the waste steam very considerably; though it is made convex and 
larger than the chimney, so as to have a larger surface, and to impede the passage as 
little as possible. The sieve is, however, but an imperfect remedy, for the cinders 
are thrown against the sieve with so much force, that the meshes are soon 
destroyed. A sieve has been tried placed at the bottom of the chimney, 
so that the blast pipe ran through it, and in this position it afforded much less 
obstruction to the draught than when placed at the top of the chimney ; for the blast of 
steam which produces the draught being entirely above it, would not be impeded, and 
the loss of power from impeding the exit of the waste steam would also be avoided. 
But the plan was afterwards abandoned, as the sieve was found to be destroyed so 
quickly as to require constant repair, from being exposed immediately to the air, and 
to all the cinders, that are drawn through the holes, striking against the front plate 
of the smoke-box, and rebounding upwards towards the chimney. 
Damper.—11, (Plates LXXXIX., XC., and XCII.,) is a damper placed in the chim 
ney just below the top of the blast pipe, consisting of a thin iron plate fitting the 
chimney closely, with a hole cut in its centre just large enough to allow the blast 
pipe to pass through. A flat bar is bolted on to it to serve as a spindle, and fixed 
a little out of the centre, in order to clear the blast pipe when the damper is elevated, 
as shewn in Plate XC. This spindle is made round at each end, and turns in bosses 
riveted to the outside of the chimney; one end passes quite through, and has a 
short lever, q, fixed on to it; the diameter of this end of the spindle is of the same 
size as the width of the flat part, to allow of the spindle being put into its place 
through the hole in the boss in which it turns, before it is attached to the damper 
in the chimney. A long rod, r r, (Plates LXXXIX. and XC.,) is attached to the 
lever, q, on the spindle, and reaches to the top of the fire-box, terminating in a 
handle, and resting in an iron fork, s, fixed in the top of the fire-box, in which either 
of two notches made in the rod can catch; so as to hold the damper either vertical, 
as in Plate XC., or in a horizontal position, closing up the chimney, as shewn by 
the dotted lines across the chimney in Plate XC. 
The damper is used to check the draught when a less intense action of the fire is 
required, such as when the engine is standing still or running down hill, and very 
little power is wanted; it causes very little obstruction to the exit of the waste 
steam, as the blast pipe passes through it. It is a curious circumstance, that whilst 
the damper is raised, the waste steam passes out of the chimney in an invisible 
state unless the atmosphere is nearly saturated with moisture, from the increased 
capacity of the hot air for moisture enabling it to absorb the steam in the chimney. 
A slight change in the dryness of the atmosphere, or the temperature of the engine 
fire, causes the steam to be visible; and hence it is always visible in winter, 
3 G