the most important improvement in the
locomotive up to that time. The steam-blast, the joint action of the
wheels by connecting them with horizontal bars on the outside, and a
simplifying connection between the cylinder and the wheels, were
embodied in the second engine, completed in 1815. For some years
Stephenson had been experimenting with the fire-damp in the mines, and
in the above year completed a miner's safety lamp, which he finally
perfected under the name of the "Gregory Lamp," which is still in use in
the Killingworth collieries. The invention of a safety lamp by Sir
Humphry Davy was nearly simultaneous, and to him the mining proprietors
presented a service of plate worth L2,000, at the same time awarding
L100 to Stephenson. This led to a protracted discussion as to the
priority of the invention, and in 1817 Stephenson's friends presented
him with a purse of $5,000 and a silver tankard.

Having now brought the locomotive to a considerable degree of
perfection, Stephenson next turned his attention to the improvement of
railways, his opinion being that both were parts of one mechanism, and
that the employment of steam carriages on common roads was
impracticable. For the purpose of making railways solid and level, and
preventing jerks at the junction of the rails, he took out a patent for
an improved rail and chair, and recommended the employment of heavier
rails, and the substitution of wrought for cast-iron. In connection with
these improvements he added considerably to the lightness and strength
of the locomotive, simplified the construction of the working parts, and
substituted steel springs for the small cylinder, on which the boiler
had at first rested.

His next important undertaking was the construction of a railway eight
miles in length, for the owners of the Helton Colliery, which was
successfully opened November 18th, 1822. The level parts were traversed
by five of Stephenson's locomotives, while stationary engines were
employed to overcome the heavy grades.

In 1820 an act of Parliament was obtained for a railway between Stockton
and Darlington, which was opened September 27th, 1825. Stephenson, who
made the preliminary surveys and specifications, was appointed engineer.
The line was intended to be worked by stationary engines for the steep
gradients, with horse-power on the level portions; but at Stephenson's
urgent request, the act was amended so as to permit the use of
locomotives on all parts