A revolving light, which gradually increases and decreases every two minutes, is exhibited on the _Fastnet Rock_, a few miles off the southernmost point of Ireland.
Of iron lighthouses the British coast presents but few examples. The reader will, therefore, be not unwilling to gain some particulars of the tower on this well-known rock; a rock rising about 60 feet above high-water mark. Its iron structure consists, in the main, of the following parts:[49]—The shell, composed of cast-iron plates; the hollow cast-iron central column; five cast-iron floors, the uppermost of which is the platform at the top of the tower, supporting the lantern; a projecting cast-iron gallery, level with the platform, sustained by cast-iron brackets, and having a balustrade; an external iron stair, for access to the doors on the first floor; internal iron stairs to connect the several floors; a lining of masonry in the basement, and of brick in the upper stories; and a cut stone moulding round the base.
[49] Practical Mechanic’s Journal for 1842, p. 265.
The principal dimensions are as follows:—
Feet. In. Height of tower from the base to the gallery 63 9 Height of lamp above the gallery 11 0 Total height of the lantern 30 0 Outside diameter at base, over stone moulding 23 0 Outside diameter over cast-iron shell 19 0 Outside diameter just below the cornice 13 11¼ Outside diameter of tower casing at light-room floor 13 8¼ Outside diameter of gallery, to outer ends of brackets 19 10¼ Inside diameter of cellar, or basement story 9 0 Inside diameter of each of the other four stories 12 0 Clear height of cellar 9 0 Clear height of each of the other four stories 12 0 Total thickness of each floor 0 9
The plates composing the cast-iron shell are curved, oblong, rectangular, and 1⅜ inch thick at the base, diminishing gradually to ⅞ inch at the top of the tower.
This lighthouse was erected in 1848, from the design of Mr. Halpin, engineer to the Corporation of Dublin.
Of lighthouses on piles we shall take as an example the _Maplin Sands Lighthouse_, designed by Mr. Walker, for the Trinity House Corporation, and erected in 1841.
It stands upon nine piles of wrought-iron, each 26 feet long and 5 inches in diameter: these are screwed 14 feet 6 inches deep into the sand, and secured by screw-blades of cast-iron, each 4 feet in diameter. One pile forms the centre of an octagon; the others are placed one at each of the eight angles. To the tops of the piles are firmly fitted hollow iron columns; the central one being perpendicular, the others bent, so that they incline inwards. They are braced together by radiating, diagonal, and horizontal rods. Each terminates at the top in a socket, into which is fitted a timber post of about one foot square. The posts, like the columns, are braced together, and form the foundation of the house, platform, and lantern.