The steam engine familiarly explained and illustrated; with an historical sketch of its invention and progressive improvement; its applications to navigation and railways; with plain maxims for railway speculators. By the Rev. Dionysius Lardner ... With additions and notes by James Renwick ...

LOCOMOTIVE ENGINES ON RAILWAYS. 167
the principle of this machine; and even were the wheels, in
the first instance, accurately constructed, it is not possible
that their wear could be so exactly uniform as to continue
equal.
(87.) The next stimulus which the progress of this invention received, proceeded from the great national work undertaken at Liverpool, by which that town and the extensive
commercial mart of Manchester wvere connected by a double
line of railway. When this project was undertaken, it was
not decided what moving power it might be most expedient
to adopt as a means of transport on the proposed road: the
choice lay between horse power, fixed steam engines, and
locomotive engines; but the first, for many obvious reasons,
was at once rejected in favour of one or other of the last two.
The steam engine may be applied, by two distinct methods, to move wagons either on a turnpike road or on a
railway. By the one method the steam engine is fixed,
and draws the carriage or train of carriages toward it by a
chain extending the whole length of road on which the
engine works. By this method the line of road over which
the transport is conducted is divided into a number of short
intervals, at the extremity of each of which an engine is
placed. The wagons or carriages, when drawn by any engine to its own station, are detached, and connected with the
extremity of the chain worked by the next stationary engine;
and thus the journey is performed, from station to station,
by separate engines., By the other method, the same engine
draws the load the whole journey, travelling with it.
The Directors of the Liverpool and Manchester railroad,
when that work was advanced toward its completion, employed, in the spring of the year 1829, Messrs. Stephenson
and Lock, and Messrs. Walker and Rastrick, experienced
engineers, to visit the different railways where practical
information respecting the comparative effects of stationary
and locomotive engines was likely to be obtained; and from