ed; and locomotives might
still have been dragging themselves unwieldily along at little more than
five or six miles an hour.

The steam-blast had scarcely been adopted, with so decided a success,
when Stephenson, observing the numerous defects in his engine, and
profiting by the experience which he had already acquired, determined to
construct a second engine, in which to embody his improvements in their
best form. Careful and cautious observation of the working of his
locomotive had convinced him that the complication arising out of the
action of the two cylinders being combined by spur-wheels would prevent
its coming into practical use. He accordingly directed his attention to
an entire change in the construction and mechanical arrangements of the
machine; and in the following year, conjointly with Mr. Dodds, who
provided the necessary funds, he took out a patent, dated the 28th of
February, 1815, for an engine which combined in a remarkable degree the
essential requisites of an economical locomotive; that is to say, few
parts, simplicity in their action, and directness in the mode by which
the power was communicated to the wheels supporting the engine.

This locomotive, like the first, had two vertical cylinders, which
communicated _directly_ with each pair of the four wheels that supported
the engine, by means of a cross head and a pair of connecting rods. But
in attempting to establish a direct communication between the cylinders
and the wheels that rolled upon the rails, considerable difficulties
presented themselves. The ordinary joints could not be employed to unite
the parts of the engine, which was a rigid mass, with the wheels lolling
upon the irregular surface of the rails; for it was evident that the two
rails of the line of way--more especially in those early days of
imperfect construction of the permanent road--could not always be
maintained at the same level,--that the wheel at one end of the axle
might be depressed into one part of the line which had subsided, whilst
the other wheel would be comparatively elevated; and in such a position
of the axle and wheels, it was obvious that a rigid communication between
the cross head and the wheels was impracticable. Hence it became
necessary to form a joint at the top of the piston-rod where it united
with the cross head, so as to permit the cross head to preserve complete
parallelism with the axle of the wheels with which it was in
communication.

In