the carr rock is a tide-covered reef extending about 1? 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 these178 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 179better 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.
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, thought180 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.”
