CARR ROCK BEACON.
1810-1821.
The Carr Rock is a tide-covered reef extending about 1¾ mile from the
shore of Fifeness, and forming a _turning point_ in the navigation
of the northern-bound shipping of the Firth of Forth, and on Mr.
Stevenson’s recommendation the Commissioners of Northern Lighthouses
resolved to erect a beacon of masonry to mark the danger.
It may seem to be unnecessary, after describing the Bell Rock
Lighthouse, to notice so apparently small a work as this; but in such
matters it is unsafe to generalise; each case must be considered on its
own merits, and great difficulties were encountered in accomplishing
the work. The formation of the Carr Rock rendered it impracticable to
secure a base for a building of greater diameter than eighteen feet,
and as part of that base had to be founded under the level of the
lowest tides by cofferdams which were removed and taken ashore after
each tide’s work, even the Engineer of the Bell Rock Lighthouse found
all his resources taxed to a considerable extent, and he was in the end
foiled in carrying out his design for the building. But irrespectively
of these physical difficulties, the Carr Rock is a work of great
interest to the lighthouse engineer, inasmuch as Mr. Stevenson at that
early date conceived the idea of calling to his aid the power given
by the rise of tide on the building to move a train of clock work to
sound a warning bell; and again, when the destruction of the upper
portion of his beacon by the sea obliged him to relinquish this plan,
unwilling to be beaten, he suggested that the same tidal action might
be made to sound a whistle; and failing that, he proposed to exhibit a
phosphorescent light from the top of the building. All of these ideas
suggested by Mr. Stevenson’s inventive mind have been from time to time
revived by modern inventors.
The original design of the Carr Rock Beacon was made in 1810, and
the work was commenced in 1813. After portions of the masonry had
repeatedly been carried away by the sea, the original design for
surmounting the building by a bell to be rung by the rise and fall
of the tide was abandoned, and the beacon was completed in 1821, by
raising an iron structure, as shown in Plate X. Fig. X-2, on the
foundation that had escaped the fury of the sea, and that structure is
still in perfect preservation. So great, indeed, was the difficulty
that Mr. Stevenson, in 1818, contemplated using blocks of cast iron
instead of stone to insure greater specific gravity--a proposal which
is believed to have been then made for the first time.
The following is Mr. Stevenson’s own description of this interesting
work:--
“The form and construction of the Carr Rock Beacon, as originally
designed and ultimately executed, will be better understood by
referring to Plate X. The motion originally intended to be given to
the bell-apparatus, or tide machine, Fig. X-1, was to be effected by
admitting the sea through a small aperture of three inches in diameter,
perforated in the solid masonry, communicating with a cylindrical
chamber in the centre of the building, measuring two feet in diameter,
in which a float or metallic air tank was to rise and fall with the
tide. During the period of flood tide, the air vessel, in its elevation
by the pressure of the water, was to give motion to machinery for
tolling the bell and winding up a weight, which last, in its descent,
during ebb tide, was to continue the motion of the machine, until the
flood tide again returned to perform the joint operation of tolling the
bell and raising the weight. A working model of a machine upon this
principle having been constructed, it was kept in motion for a period
equal to several months; this was effected by water run through a
succession of tanks raised by a pump from the lower one to the higher,
thus producing the effect of flood and ebb tides. The time during which
this apparatus was in action having been ascertained by an index, a
constant attendance upon the machine during this protracted experiment
became unnecessary.
[Illustration:
_PLATE X._
CARR ROCK BEACON AS DESIGNED IN THE YEAR 1810
CARR ROCK BEACON AS EXECUTED IN THE YEAR 1821]
“The upper termination of the beacon, in its present form, as shown in
Fig. X-2, does not admit of the application of the tide machine with
the bell apparatus. Experiments as applicable to this have, however,
been tried with a wind instrument, to be sounded by the pressure of the
sea water, but it has not succeeded to the extent that seems necessary
for a purpose of this kind. We have, indeed, thought that the
application of pressure as a power, communicated by the waters of the
ocean, in mechanical operations, might be carried to almost any extent
by simply providing a chamber or dock large enough for the reception of
a float or vessel, of dimensions equivalent to the force required. This
description of machinery is more particularly applicable in situations
where the tides have a great rise, as in the Solway Firth, Bristol
Channel, and other parts of the British seas; and at St. Malo on the
coast of France.
“A beacon of any form, unprovided with a light, must always be
considered an imperfect landmark, and therefore various modes have
been contemplated for more completely pointing out the position of
the Carr Rock. It has been proposed that phosphoric lights should be
exhibited from the top of the building. This object, however, would
be more certainly accomplished by the erection of leading lights upon
the island of May and mainland of Fife. But these, with other plans,
which have been under the writer’s consideration, would necessarily
be attended with a great additional expense, which, in the present
instance, it is not thought advisable to incur.”