ch was immediately proceeded with at the
Newcastle works.

The principal circumstances connected with the construction of the
"Rocket," as described by Robert Stephenson to the author, may be briefly
stated. The tubular principle was adopted in a more complete manner than
had yet been attempted. Twenty-five copper tubes, each three inches in
diameter, extended from one end of the boiler to the other, the heated
air passing through them on its way to the chimney; and the tubes being
surrounded by the water of the boiler, it will be obvious that a large
extension of the _heating surface_ was thus effectually secured. The
principal difficulty was in fitting the copper tubes within the boiler so
as to prevent leakage. They were made by a Newcastle coppersmith, and
soldered to brass screws which were screwed into the boiler ends,
standing out in great knobs. When the tubes were thus fitted, and the
boiler was filled with water, hydraulic pressure was applied; but the
water squirted out at every joint, and the factory floor was soon
flooded. Robert went home in despair; and in the first moment of grief,
he wrote to his father that the whole thing was a failure. By return of
post came a letter from his father, telling him that despair was not to
be thought of--that he must "try again;" and he suggested a mode of
overcoming the difficulty, which his son had already anticipated and
proceeded to adopt. It was, to bore clean holes in the boiler ends, fit
in the smooth copper tubes as tightly as possible, solder up, and then
raise the steam. This plan succeeded perfectly, the expansion of the
copper tubes completely filling up all interstices, and producing a
perfectly watertight boiler, capable of withstanding extreme internal
pressure.

The mode of employing the steam-blast for the purpose of increasing the
draught in the chimney, was also the subject of numerous experiments.
When the engine was first tried, it was thought that the blast in the
chimney was not strong enough to keep up the intensity of the fire in the
furnace, so as to produce high-pressure steam in sufficient quantity.
The expedient was therefore adopted of hammering the copper tubes at the
point at which they entered the chimney, whereby the blast was
considerably sharpened; and on a further trial it was found that the
draught was increased to such an extent as to enable abundance of steam
to be raised. The rationale of the blast may be simply explain