reat Britannia tubes was a still more
formidable enterprise, though the experience gained at Conway rendered it
easy compared with what it otherwise would have been. Mr. Stephenson
superintended the operation of floating the first in person, giving the
arranged signals from the top of the tube on which he was mounted, the
active part of the business being performed by a numerous corps of
sailors, under the immediate direction of Captain Claxton. Thousands of
spectators lined the shores of the Strait on the evening of the 19th
June, 1849. On the land attachments being cut, the pontoons began to
float off; but one of the capstans having given way from excessive
strain, the tube was brought home again for the night. By next morning
the defective capstan was restored, and all was in readiness for another
trial. At half-past seven in the evening the tube was afloat, and the
pontoons swung out into the current like a monster pendulum, held steady
by the shore guide-lines, but increasing in speed to almost a fearful
extent as they neared their destined place between the piers. "The
success of this operation," says Mr. Clark, "depended mainly on properly
striking the 'butt' beneath the Anglesey tower, on which, as upon a
centre, the tube was to be veered round into its position across the
opening. This position was determined by a 12-inch line, which was to be
paid out to a fixed mark from the Llanfair capstan. The coils of the
rope unfortunately over-rode each other upon this capstan, so that it
could not be paid out. In resisting the motion of the tube, the capstan
was bodily dragged out of the platform by the action of the palls, and
the tube was in imminent danger of being carried away by the stream, or
the pontoons crushed upon the rocks. The men at the capstan were all
knocked down, and some of them thrown into the water, though they made
every exertion to arrest the motion of the capstan-bars. In this dilemma
Mr. Rolfe, who had charge of the capstan, with great presence of mind,
called the visitors on shore to his assistance; and handing out the spare
coil of the 12-inch line into the field at the back of the capstan, it
was carried with great rapidity up the field, and a crowd of people, men,
women, and children, holding on to this huge cable, arresting the
progress of the tube, which was at length brought safely against the butt
and veered round. The Britannia end was then drawn into the recess of
the masonry