orming the Liverpool and Manchester Railway embankments, was constructed
with a double tube, each of which contained a fire and passed
longitudinally through the boiler. But this arrangement necessarily led
to a considerable increase in the weight of the engine, which amounted to
about twelve tons; and as six tons was the limit allowed for engines
admitted to the Liverpool competition, it was clear that the time was
come when the Killingworth locomotive must undergo a further important
modification.

For many years previous to this period, ingenious mechanics had been
engaged in attempting to solve the problem of the best and most
economical boiler for the production of high-pressure steam. As early as
1803, Mr. Woolf patented a tubular boiler, which was extensively employed
at the Cornish mines, and was found greatly to facilitate the production
of steam, by the extension of the heating surface. The ingenious
Trevithick, in his patent of 1815, seems also to have entertained the
idea of employing a boiler constructed of "small perpendicular tubes,"
with the same object of increasing the heating surface. These tubes were
to be closed at the bottom, and open into a common reservoir, from which
they were to receive their water, and where the steam of all the tubes
was to be united.

About the same time George Stephenson was trying the effect of
introducing small tubes in the boilers of his locomotives, with the
object of increasing their evaporative power. Thus, in 1829, he sent to
France two engines constructed at the Newcastle works for the Lyons and
St. Etienne Railway, in the boilers of which tubes were placed containing
water. The heating surface was thus found to be materially increased;
but the expedient was not successful, for the tubes, becoming furred with
deposit, shortly burned out and were removed. It was then that M.
Seguin, the engineer of the railway, pursuing the same idea, adopted his
plan of employing horizontal tubes through which the heated air passed in
streamlets. Mr. Henry Booth, the secretary of the Liverpool and
Manchester Railway, without any knowledge of M. Seguin's proceedings,
next devised his plan of a tubular boiler, which he brought under the
notice of Mr. Stephenson, who at once adopted it, and settled the mode in
which the fire-box and tubes were to be mutually arranged and connected.
This plan was adopted in the construction of the celebrated "Rocket"
engine, the building of whi