possibility of steam locomotion had become an object of general
inquiry or of public interest.

It has already been observed that up to, and indeed after, the period of
which we speak, there was no such class of skilled mechanics, nor were
there any such machines and tools in use, as are now available to
inventors and manufacturers. Although skilled workmen were in course of
gradual training in a few of the larger manufacturing towns, they did
not, at the date of Stephenson's patent, exist in any considerable
numbers, nor was there then any class of mechanics capable of
constructing springs of sufficient strength and elasticity to support
locomotive engines of ten tons weight.

In order to avoid the dangers arising from the inequalities of the road,
Stephenson so arranged the boiler of his new patent locomotive that it
was supported upon the frame of the engine by four cylinders, which
opened into the interior of the boiler. These cylinders were occupied by
pistons with rods, which passed downwards and pressed upon the upper side
of the axles. The cylinders opening into the interior of the boiler,
allowed the pressure of steam to be applied to the upper side of the
piston; and the pressure being nearly equivalent to one-fourth of the
weight of the engine, each axle, whatever might be its position, had at
all times nearly the same amount of weight to bear, and consequently the
entire weight was pretty equally distributed amongst the four wheels of
the locomotive. Thus the four floating pistons were ingeniously made to
serve the purpose of springs in equalising the weight, and in softening
the jerks of the machine; the weight of which, it must also be observed,
had been increased, on a road originally calculated to bear a
considerably lighter description of carriage. This mode of supporting
the engine remained in use until the progress of spring-making had so far
advanced that steel springs could be manufactured of sufficient strength
to bear the weight of locomotive engines.

[Picture: Old Killingworth Locomotive, still in use]

The result of the actual working of the new locomotive on the improved
road amply justified the promises held forth in the specification. The
traffic was conducted with greater regularity and economy, and the
superiority of the engine, as compared with horse traction, became still
more marked. It is a fact worthy of notice, that the identical engines
constructed in 1816 afte