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.
Plate III.
GENERAL CHART, SHEWING THE RELATIVE POSITION OF THE BELL ROCK.
CHART
shewing the relative situation
of the
BELL ROCK LIGHT HOUSE.
Drawn by J. Steedman
Engd. by W. H. Lizars