The life of George Stephenson, railway engineer - Lighthouse ...

252 LIFE OF GEORGE STEPHENSON. [chap. xxi.
its velocity ; but Mr. Stephenson held, what has since been
clearly established, that, instead of the steam becoming ex-
hausted, and the working power of the locomotive lessened, in
proportion to its speed, the result was the very reverse, and that
the expenditure of steam was, by means of the important con-
trivance of the blast, made subservient, through the more intense
combustion of fuel which it excited, to the increased production
of power in the engine.*
The directors could not fail to have been influenced by these
arguments. But the fixed-engine party was very strong at the
* This principle was afterwards clearly illustrated by Mr. Robert Stephensoa
in the joint essay entitled " Observations on the Comparative Merits of Locomotive
and Fixed Sngines," published by himself and Mr. Locke (as compiled from the
Reports of Mr. George Stephenson) in reply to the Report of Mr. James Walker,
C. E. The pamphlet was published in February, 1839.
Mr. Robert Stephenson there observes ;— '
" In locomotive engines hitherto constructed, the area of the surface in the
boiler acted upon by the fire is much less than that generally employed in sta-
tionary engines ; and hence It is that the consumption has been much greater
to produce equal effects. This inconvenience has been submitted to, in order
that simplicity and compactness might be achieved.
" To compensate for the loss of heating surface, it was necessary to augment
the temperature of the fire. This was effected, shortly after the first locomo-
tive engine was tried on the Killingworth Colliery Railway, by conveying the
steam into the chimney, where it escaped in a perpendicular direction up the
centre, after it had performed its office in the cylinders. The velocity of the
steam on entering the chimney being much greater than that due to the ascending
current of air from the natural draft of the furnace, the effect was to in-
crease the draught, and consequently the temperature of the fire
Since it has been shown that the power of these engines, under similar cir-
cumstances, is chiefly dependent on the quantity of fuel consumed, it is evident
that, by this application of the waste steam to accelerate combustion, the power
of the engine actually varies under different velocities. This curious fact, connected
with the construction of locomotive engines on the principle of the
' Rocket,' has not hitherto, we believe, been represented in this manner; and it
is so important, that any calculation neglecting its consideration, at high veloc-
ities, must be regarded as futile and absolutely false.
" Mr. Walker takes the power of a locomotive engine, of the size and con-
struction of those used upon the Darlington Railway, equal to 10 horses, at 2J
miles an hour. Presuming that the effect is inversely as the velocities, he re-
duces the power of the engine at 10 miles an hour to 2^ horses' power, or
= 375 lbs. This conclusion would have been perfectly correct if the quantity
of steam generated in the boiler in equal times were the same at all velocities;
but the fallacy of this assumption, in reference to locomotive engines, has been
sufficiently explained in the foregoing remarks." Observations, ^c, pp. 6-8.
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