NORTH UNST, 1854.—SUNDERLAND, 1841.
The erection of the North Unst tower, completed in 1854, offered
no difficulties comparable to those which tested the skill and
perseverance of the builder of the Bell Rock; yet, not the less, it
is interesting as one of the most important results obtained by our
English engineers. As our illustration shows, it stands rooted on an
isolated reef, near the Shetland Isles, whose elevation above the sea
is estimated at 200 feet.
Its northern front is almost perpendicular, and exposed to the most
violent assaults of Ocean; on the south the declivity is less abrupt,
but scarcely easier of access; and its summit is only of breadth
sufficient to receive the foundation of the tower. This is 50 feet
in height, and contains, besides the light-room, a sleeping chamber,
a kitchen, and a store-room. At its base is built an additional
store-room for the supplies of oil, charcoal, and fresh water. It is
only accessible in fine weather.
The North Unst lighthouse is provided with a staff of four keepers,
whose habitations are situated on the island of Unst (one of the
Shetland group), about four miles distant.
It has justly been said that one of the strangest operations recorded
in the history of lighthouses is, undoubtedly, the work undertaken
and successfully accomplished at Sunderland in 1841. Some important
improvements had been effected in its harbour; and a jetty had been
constructed which rendered useless the old pier, and the lighthouse
built upon it. Consequently, preparations were made for the demolition
of the latter. An engineer, of the name of Murray, however, conceived
the idea of transporting the monument, in one piece, to the intended
site of the new lighthouse, a distance of about 475 feet. His proposal
was favourably received; for the removal of great masses of masonry,
in Europe at least, is an enterprise which always excites a very
general curiosity. In the United States, that “go-ahead” land of bold
projects and daring inventions, such enterprises are more frequent,
and the process has been several times applied to houses (as recently
at Chicago) and factories, for which it was desirable to secure a more
convenient or a securer site. In such cases a series of openings is
made in the walls, and through these openings beams are introduced,
united together by cross beams so as to form a kind of flooring; then
the lowest part of the base of the walls is destroyed, leaving the
building to rest upon the timber platform, which is afterwards set in
motion by a system of grooves.
[Illustration: NORTH UNST LIGHTHOUSE.]
So far as concerned the Sunderland lighthouse, the enterprise was
much more arduous; for its narrow base supported a burden relatively
more considerable than that of a house, and one which apparently must
crush all machines interposed between it and the ground. The weight
of the lighthouse was 757,000 lbs.; it consisted of an octagonal
tower 64 feet high, and 15 feet in diameter at the base. We must add
that the new pier was 19 inches higher than the old, and that its
direction was entirely different; which rendered it necessary that the
building should be turned upon its axis, at the same time that it had
to traverse a broken line, one of whose sections, from north to south,
measured 28 feet, and the other, from west to east, 447 feet.
The accompanying illustration will afford an idea of the manner in
which this difficult engineering problem was solved. By means of a
series of openings made in the base of the tower, as above described,
the latter was raised on a solid platform of oaken planks; while it
was surrounded from base to summit by a framework of stays or props,
strengthened by cross beams. The platform rested on one hundred and
forty-four cast-iron wheels, grooved like those of a locomotive, and
running on eight parallel rails, likewise of cast-iron, which, with
their “sleepers,” were laid along the masonry of the pier and jetty.
When the mass had moved a few feet, the rails were lifted, and laid
down again in front of the machinery, and this process was repeated
until the new site of the lighthouse was reached. Iron chains attached
to the platform were wound upon windlasses, worked by a band of sturdy
labourers.
The various stages of the operation were accomplished in thirteen
hours and twenty-four minutes. The combined efforts of forty men were
required for five hours to carry the apparatus over the 28 feet of the
first section, while eighteen men sufficed to carry it in eight hours
and twenty-four minutes over the 447 feet of the second.
In this latter part the rails were at first laid down on a curve, so as
to bring the pharos into a symmetrical position with the jetty, then
it advanced parallel to itself, following a slightly inclined plane.
It was prevented by wedges from deviating during this ascent from a
perpendicular line. The object of this twofold disposition was to
veer the pharos round, and to raise it to a higher level—which, as we
have seen, was an indispensable condition. The removal was eventually
accomplished with so much success, and so little interruption to the
business of the harbour, that the lamp was lighted in the evening at
the usual hour.
[Illustration]
[Illustration: TRANSPORTING A LIGHTHOUSE—SUNDERLAND.]
[Illustration]