An Account of the Bell Rock Light-House / Including the Details of the Erection and Peculiar Structure of That Edifice; to Which Is Prefixed a Historical View of the Institution and Progress of the Northern Light-Houses

by Robert Stevenson

Practical conclusions about the period of completing the Works, and mode of distinguishing the Light.

Having, in the course of the two last seasons, landed and built upwards of 1400 tons of stone upon the Bell Rock, while the work was low in the water, and before the Beacon was habitable, and finding that it did not now require more than about 700 tons to complete the masonry, the writer concluded, that, barring accidents of a very untoward nature, there was every prospect of the Light-house being finished in the course of the ensuing season. A question, of much importance, however, still remained in some measure undetermined, regarding the characteristic description of the light most suitable for the Bell Rock, so as to render it easily distinguishable from all others upon the coast. There being Stationary-lights already in the Firth of Forth; this mode could not be adopted for the Bell Rock. Revolving-lights had also lately been erected upon the Fearn Islands, the most contiguous Light-house-station to the southward, as will be seen from the General Chart of the coast in [Plate III.] Considering, therefore, the liability of the mariner to mistake the appearance of lights in stormy weather, or from an error in his course in returning from a distant voyage, it was of the last importance that the Bell Rock Light-house should be easily distinguishable. The most suitable means for accomplishing this seemed to be by the exhibition of different colours from the same Light-room. The only colour which had yet been found to answer, was produced by interposing shades of red glass before the reflectors. But this was the colour used for distinguishing the Light of Flamborough-head, on the Yorkshire coast, and, though about 169 miles to the southward, it would still have been desirable to have avoided the same colour. A train of experiments was therefore made from Inchkeith Light-house, with plates of glass, coloured red, green, orange, yellow, blue, and purple, procured from Birmingham and London. These were fitted to the reflectors at Inchkeith, within view of the writer’s windows in Edinburgh. The Tender was likewise appointed to cruise, that more distant observations might be made, for ascertaining the effect of these coloured shades. But after the most full and satisfactory trials, the red colour was found to be the only one applicable to this purpose. In tolerably clear weather, the light of one reflector tinged red, alternating with a light of the natural appearance, with intervals of darkness, was easily distinguishable at the distance of eight or nine miles; while the other colours rendered the light opaque, being hardly distinguishable to the naked eye at more than two or three miles. After various trials and observations made in this manner, both on land and at sea, the writer at length resolved on recommending the use of red, as the only colour suitable for this purpose; and, in order to vary the light as much as possible from that of Flamborough-head, a square Reflector-frame was adopted at the Bell Rock, with two of its faces or sides having red coloured shades, and the other two exhibiting lights of the natural appearance. At Flamborough-head, the Reflector-frame is triangular, and on one side it is furnished with red coloured shades, while the other two sides exhibit lights of the natural appearance. The design at the Bell Rock, on the contrary, was to exhibit a light tinged red, alternating with one of the natural appearance; and, upon this principle, the apparatus was put in a state of preparation.

1810, March.

State of the Works at Arbroath.

In the work-yard at Arbroath things were going forward very prosperously, at the sight of Mr David Logan, clerk of works. The hewing or preparation of the stones for the Light-house was now advanced to within about eight courses of the cornice, which, with the parapet, as already observed, was all set up at Edinburgh, and ready for being shipped when wanted at the Rock. A kiln of the Aberthaw limestone having already been calcined, was partly reduced to the state of powder, and put up into casks, as formerly. The operation of pounding the lime was very tedious and unpleasant, being performed by labourers upon a stone-bench in the lime-house, where it was reduced chiefly by means of friction, between the bench and stones, managed by hand. Due proportions of pozzolano-earth and clean sharp sand were made up in casks, and the oaken trenails and wedges in bundles; but the supply wanted of these materials was, in future, to be comparatively trifling. The building being now considerably above the rise of the tide, the use of mortar was less, while the system of trenailing and wedging was to be discontinued, after the building had reached the top of the stone staircase, or to the height of 13 feet above the solid. The several implements connected with the building operations being also laid to hand, nothing was now required but good weather and favourable tides, to proceed with the works at the Rock.

Gangway or Bridge for the Rock.

1810, April.

Among the preparations at Arbroath for the furtherance of the work at the Bell Rock, was the construction of a gangway or bridge of timber between the Beacon and the Building, instead of the Rope-ladder employed with so much effect last season, as will be understood by examining the second and third years’ work, represented in [Plate IX.] This more stable and commodious way of communicating with the works, was also to be useful as a stage for raising the building materials, instead of the lower crane, the stool or prop of which had become too low, and, as before noticed, had been washed away by the sea in the course of last month. This bridge consisted of two principal beams of Memel timber, measuring 44 feet in length, 6 inches in thickness, and 13 inches in depth. At one end these beams were to abut against the principal beams of the Beacon, and to be strongly bolted to them; at the opposite end, one was to be rested on the sole or instep of the door, while the other was to be let 6 inches into a hole cut into the upper granite course of the Light-house. They were placed 7 feet apart, and formed a roadway of 6 feet in breadth between the rails, which was strongly bound in a lateral direction with cross framing mortised into the principal beams, and otherwise fixed with screw-bolts. The bridge was further to be supported by four diagonal spur-beams, which met in pairs on each side, at the middle of the roadway, and there formed king-posts, to steady and support it. A crab or winch-machine was to be placed upon it, for raising the stones at once from the rock to the level of the top of the solid part of the building.

Wednesday, 18th.

Operations commence for the season. Wooden Bridge is erected.