From the vicinity of Inchkeith to sandstone quarries, the buildings there were executed of aislar masonry. A platform roof covered with lead, and defended by a parapet wall, was adopted for the light-keepers’ house, instead of a slated roof, with garrets of the common construction; a slated roof being not only more liable to be injured by high winds, but when the attic apartments of such houses are occupied, the premises became more exposed to accident from fire.
Disadvantage of slated roofs.
Construction of Light rooms improved.
An entire change also took place at this period upon the construction of the Light-rooms and the reflecting apparatus, as well as in the extension and enlargement of the accommodation for the light-keepers. The early light-rooms were constructed wholly of timber, excepting the window-sash frames, which were made of cast-iron. The outside of the wooden cupola, covered with sheet copper, and the ceiling and floor with fire-proof plates of tinned iron. But it soon appeared that this construction was liable to great objections, particularly to the risk of accidental fire. The timber roof being also unavoidably shut up from the air, and exposed to a degree of heat sufficient to dry it to the state of tinder, its strength and fibrous qualities were soon lost, and the buildings in danger of being destroyed by the storms of winter.
Rendered Fire-proof.
Reflectors of Silvered Mirror-glass.
The reflectors of the first of the Northern Light-houses were formed to the parabolic curve, upon principles susceptible of considerable accuracy; their powers were, however, small from their reflecting surfaces being composed of facets of silvered mirror-glass, and one point only of each facet coinciding with the curve of the parabola. As many of the rays are thus lost or weakened by transmission through the glass of the reflector, the light is much less brilliant than when reflected from a metallic speculum of a uniform parabolic figure, of a more white and dense body, such as silver. Another objection to mirror-glass reflectors, is the great number of interstices or subdivisions between the pieces of glass, which unavoidably induces a want of cleanliness and uniformity in the reflecting surface as a whole.
Reflectors of Copper, plated with Silver.
The use of Argand lamps and Spermaceti Oil introduced.
Inscription on Inchkeith Light-house.