Plate II. — Carr Rock Beacon
Pl. II.
The Carr Rock Beacon is represented in Plate II. and referred to in the introduction at page 53. The diagram marked Figure 1. is an outline of the rock, shewing the position of the beacon, and plan of the first course of the building, made to a radius of nine feet, cut in a dove-tailed form, after the manner of the courses of the Edystone and Bell Rock Light-houses.
Figure 2. is a section of the rock on the line A, B, Fig. 1. with a perpendicular section also of a tower of masonry and apparatus, for tolling an alarm-bell, which was originally intended for this situation. In Fig. 2. letter a represents an aperture measuring 3 inches in diameter, which was perforated with much labour and care through a block of granite 7 feet in length, previously to its being laid. This canal was intended to admit the tidal-waters into the interior chamber of the building marked b, in which the flood-tide was to act upon an air-tight copper-tank, marked c, and its rod of connection formed into a rack with teeth, by which motion was to be given to a train of machinery, represented at d in the void of the building. The machine was to act on the vertical shaft e, connected with a series of hammers f, placed under the great bell g, which was to have measured 5 feet in diameter, and become the cupola or roof of the building. In this manner the bell was to be tolled to forewarn the mariner of his approach to the dangers of the Carr, and the other extensive ledges of sunken rocks in its neighbourhood. By the rise of the flood-tide, and consequent admission of the waters into the canal a, the tank c, with its connecting rod, not only lifted the bell-hammers f, and, at the same time, also elevated the weight marked h, which, in its descent during ebb-tide, was to have continued the motion of the machinery; and thus, by the alternate operation of the tides, the continual tolling of the Bell was to have been preserved.
It will further be seen from the section of this building, that the masonry of the solid is connected perpendicularly by means of stone-joggles inserted half into the one course and half into the other. But in the void or upper part, instead of the joggles, the bed-joints of the stones were let or sunk about an inch in depth, into each other, as at the Bell Rock, forming so many bands or girths to the work. This will be observed by narrowly examining the section at letter i, with its accompanying diagram Fig. 3., which represents a plan of one of the courses of the void, shewing how the stones were connected horizontally by a system of dove-tailing, as is further represented in Fig. 4., being a plan of a course at the level a, k, in which the perforation is delineated for the admission of the tidal-waters.
The ascent to this building was to have been by means of a ladder of cast-iron or flight of steps, marked a, i, l, fixed on the outward wall by means of screw-bolts fixed into brass-bats, sunk into the masonry, and run up with lead. The entrance-door of this building was formed in the cast-iron frame or pedestal on which the great bell was to have been supported, the access to the interior being by the balcony, round which a cast-iron rail was intended, not only for the safety of the keepers or occasional attendants, but also, in some measure, to defend the bell from the sprays of the sea.
Figure 5. represents the Pillar-formed Beacon, as finished at the Carr Rock in the year 1821. The lower part of this diagram is a perpendicular section of the rock on the line A B, Fig. 1. The masonry is also shewn with two of the six great malleable iron-bats or stancheons marked a in Fig. 5., which passing through the several courses, are sunk about 30 inches into the Rock. The upper part of this diagram represents a frame of cast-iron work, of great strength, fashioned somewhat after the manner of what seamen term a spar or spur beacon, from being made generally of timber, set up in the form of struts or spur-beams. The connection of this frame will be understood from the detached diagram Fig. 6., taken upon the line or level marked b in Fig. 5. From Figs. 5. and 6. it will be observed, that the beacon consists of 6 pipes or hollow tubes, marked letter A, which are inserted into the sockets c, in the sill-plate of Fig. 6, into which these hollow tubes are strongly wedged and keyed with culter or spear bolts, which pass through each of the sockets and base of the hollow tubes at c. Besides the main hollow tubes marked A, other six marked B, are set up as spurs or diagonals, which radiate from sockets cast in the centre of the sill-plate marked e. These diagonals are so situated, and connected by dove-tail or hook-joints, that they butt against the main tubes, and support them at f. The main tubes are further connected by means of horizontal bars of malleable iron, marked g in Fig. 5, laid into grooves formed in the arms of the cast-iron collars F, k, which clasp around the main tubes at these points, immediately above and below their connection with the diagonal tubes. These collars are also keyed with the main tubes by means of spear-bolts. At the point of junction d d, towards the top, the main tubes form segments of a common circle, and rest upon the centre block h, into which they are keyed and wedged. As a further security, a strong cast-iron tubular formed case, marked i i, is made to clasp around the whole upper parts of the main tubes at their point of junction d d, so as to form a girth to them. This tubular case or cap i i, is 8 feet in length, and terminates with a cast-iron ball marked m m, which is 3½ feet in diameter, formed into ribs, connected with the cap i i, by means of a socket, through which a spear-bolt passes, and binds it to the top of the tubular-case at the point l.
Fig. 6. represents the Ballast-plate, which forms the sill or basement of the superstructure. It contains about 8 tons of cast-iron, and is so constructed as to become a cap or girth to the upper course of the masonry which it is calculated to secure, by means of a flange of 6 inches in depth at the outward extremity, marked b b in Fig. 5, where it is let into the stone. This plate is cast in six pieces, connected together at the points m m m m m m, by means of screw-bolts of one and a half inch in diameter (with nuts), passing through flanges raised at the joints of its several compartments. At the points n n n n n n, there were six socket-holes, for the reception of the great stancheons or bolts, marked a a, Fig. 5, which, passing through the masonry, are sunk 30 inches into the Rock, where they are fixed at the lower ends with iron-wedges, driven home by means of a long iron-driver. The ballast-plate is connected with the upper ends of these great stancheons, by means of a shackle and bolt, in such a manner that the more exposed parts may be renewed. The whole is imbedded and run up with pozzolano-mortar, so as to preserve the several parts as much as possible from the effects of oxidation.
Fig. 7. represents a horizontal section of this beacon, on the line F F, shewing the connection of the horizontal malleable iron-bars or braces g g g g, which fit into the grooves of the arms of the collars, embracing the hollow tubes or pillars A A A A, and connecting them by means of spear-bolts at k k k k. The grooves in these arms are so formed as to command the braces, and to contain a quantity of Parker’s or Roman cement, by which the bolts are preserved from the effects of oxidation. These collars and arms, with their connecting malleable iron-bars, form a girth immediately above the diagonal struts or braces B B B, Fig. 5. A similar chain of connection is in like manner formed below the junction of these diagonal struts, with the main tubes, which, like those described above, has the effect of binding the whole fabric horizontally.
Fig. 8. is a horizontal section upon the line d d, delineated upon a scale of double the size of the other parts of the beacon, shewing the connection of the hollow tubes A A A A A A, at the top, where they change their cylindrical form into segments of a circle at the point of contact, so as to embrace the centre-block h h. The top of these tubes thus formed into a compact figure, is cased or covered with the cylindrical cap i i, through which the spear-bolts immediately above and below the points d d, in Fig. 5, are made to pass and bind the whole firmly together.