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

80 LIFE OP GEOEGE STEPHENSON. [chap. vin.
Trevethick having abandoned the locomotive for more promis-
ing schemes, no further progress was made with it for some
years. An imaginary difficulty seems to have tended, amongst
other obstacles, to prevent its adoption and improvement. This
was the supposition that, if any heavy weight were placed
behind the engine, the " grip " or " bite " of the smooth wheels of
the locomotive upon the equally smooth iron rail, must neces-
sarily be so slight that the wheels would slip round upon the
rail, and, consequently, that the machine would not make any
progress. Hence Trevethick, in his patent, recommended that
the periphery of the driving-wheels should be made rough by
the projection of bolts or cross-grooves, so that the adhesion of
the wheels to the road might be secured. This plan was adopted
in Trevethick's engine tried on the Merthyr Tydvil Railway,
and its progress must therefore necessarily have been a succes-
sion of jolts, very trying to the cast-iron plates of the coUiery
tram-road.
Following up the presumed necessity for a more effectual
adhesion between the wheels and the rails than that presented
by their mere smooth contact, Mr. Blenkinsop, of Leeds, in
1811, took out a patent for a racked or tooth-rail laid along one
side of the road, into which the toothed-wheel of his locomotive
worked as pinions work into a rack. The boiler of his engine
was supported by a carriage with four wheels without teeth, and
rested immediately upon the axles. These wheels were entirely
independent of the working parts of the engine, and therefore
merely supported its weight on the rails, the progress being
effected by means of the cogged wheel working into the cogged-
rail. The engine had two cylinders instead of one, as in Treve-
thick's engine. The invention of the double cylinder was due
to Matthew Murray, of Leeds, one of the best mechanical engi-
neers of his time, Mr. Blenkinsop, who was not himself a
mechanic, having consulted him as to all the practical arrange-
ments of his locomotive. The connecting-rods gave the motion
to two pinions by cranks at right angles to each other ; these
pinions communicating the motion to the wheel which worked
into the toothed-rail.
Mr. Blenkinsop's engines began running on the railway