hair upon which the
rails rested being tilted by unequal subsidence, the end of one rail
became depressed, whilst that of the other was elevated. Hence constant
jolts and shocks, the reaction of which very often caused the fracture of
the rails, and occasionally threw the engine off the road.

To remedy this imperfection Mr. Stephenson devised a new chair, with an
entirely new mode of fixing the rails therein. Instead of adopting the
_butt-joint_ which had hitherto been used in all cast-iron rails, he
adopted the _half-lap joint_, by which means the rails extended a certain
distance over each other at the ends, like a scarf-joint. These ends,
instead of resting upon the flat chair, were made to rest upon the apex
of a curve forming the bottom of the chair. The supports were also
extended from three feet to three feet nine inches or four feet apart.
These rails were accordingly substituted for the old cast-iron plates on
the Killingworth Colliery Railway, and they were found to be a very great
improvement upon the previous system, adding both to the efficiency of
the horse-power, still employed in working the railway, and to the smooth
action of the locomotive engine, but more particularly increasing the
efficiency of the latter.

[Picture: Half-lap Joint]

This improved form of rail and chair was embodied in a patent taken out
in the joint names of Mr. Losh, of Newcastle, iron-founder, and of Mr.
Stephenson, bearing date 30th September, 1816. Mr. Losh being a wealthy,
enterprising iron-manufacturer, and having confidence in George
Stephenson and his improvements, found the money for the purpose of
taking out the patent, which, in those days, was a very costly as well as
troublesome affair.

The specification of the same patent also described various important
improvements in the locomotive itself. The wheels of the engine were
improved, being altered from cast to malleable iron, in whole or in part,
by which they were made lighter as well as more durable and safe. But
the most ingenious and original contrivance embodied in this patent was
the substitute for springs which Mr. Stephenson invented. He contrived
that the steam generated in the boiler should perform this important
office. The method by which this was effected displayed such genuine
mechanical genius, that we would particularly call attention to the
device, which was the more remarkable, as it was contrived long before
the