“It formed part of the writer’s original design to erect a cast iron cofferdam of about five feet in height round the site of the building; but the surface of the rock was so irregular that the difficulty of tightening it, and also of emptying the contained water, so as to get the benefit of it during ebb tide, would have been so great, that taking these circumstances into account, together with the loss of time which would attend the erection of such a preparatory work, the idea of a cofferdam was laid aside, soon after entering upon the actual execution of the work.”
BUOYAGE SYSTEM.
In his report on the Forth Navigation, made to the Magistrates of Stirling in 1828, Mr. Stevenson proposed a system of buoyage, which has since been adopted by the several Lighthouse Boards of the United Kingdom:—
“The channels proposed to be cleared through the different fords are coloured red on the Plan, in reference to the sectional line. For the use and guidance of river pilots, buoys and perches or beacons are likewise intended to be placed in the positions shown in the Plan; those coloured red are to be taken on the starboard, and those coloured black upon the larboard side, in going up the river; and the whole are to be so placed in connection with the clearing and deepening of the fords as to be approached with safety.”
OBSERVATIONS ON FOG SIGNALS.
At a very early period Mr. Stevenson’s attention was directed to the dangers of fog at sea, and the best means of providing an effective fog signal for the mariner, and so long ago as 1808 he had come to the conclusion that the best signal adapted for the purpose was the sustained sound of a horn, which, as is well known, has within the last few years been so much employed in the fog signals which are now being established at many of the lighthouse stations in this and foreign countries. The following extracts give an idea of the difficulties he encountered, and his views on the subject:—
“The boats landed this evening (23d June 1808), when the artificers had again two hours’ work. The weather still continuing very thick and foggy, more difficulty was experienced in getting on board of the vessels to-night than had occurred on any previous occasion, owing to a light breeze of wind which carried the sound of the bell, and the other signals made on board of the vessels, away from the rock. Having fortunately made out the position of the sloop “Smeaton,” at the north-east buoy, to which we were much assisted by the barking of the ship’s dog, we parted with the Smeaton’s boat, when the boats of the tender took a fresh departure for that vessel, which lay about half a mile to the south westward. Yet such is the very deceiving state of the tides that although there was a small binnacle and compass in the landing master’s boat, we had nevertheless passed the ‘Sir Joseph’ a good way, when fortunately one of the sailors caught the sound of a blowing horn. The only fire-arms on board were a pair of swivels of one inch calibre; but it is quite surprising how much the sound is lost in foggy weather, as the report was heard but at a very short distance. The sound from the explosion of gunpowder is so instantaneous that the effect of the small guns was not so good as either the blowing of a horn or the tolling of a bell, which afforded a more constant and steady direction for the pilot. It may here be noticed that larger guns would have answered better, but these must have induced the keeping of a greater stock of gunpowder, which in a service of this kind might have been attended with risk. A better signal would have been a bugle horn, the tremulous sound of which produces a more powerful effect in fog than the less sonorous and more sudden report of ordnance.”
And again he says:—
“In the course of this morning’s work two or three apparently distant peals of thunder were heard, and the atmosphere suddenly became thick and foggy. But as the Smeaton, our present tender, was moored at no great distance from the rock, the crew on board continued blowing a horn, and occasionally fired a musket, so that the boats got to the ship without difficulty. The occurrence of thick weather, however, became a serious consideration in looking forward to the necessary change of quarters to the Pharos, distant about one mile from the rock, instead of a few hundred yards, as in the case of the Smeaton.
“The weather towards the evening became thick and foggy, and there was hardly a breath of wind to ruffle the surface of the water; had it not therefore been the noise from the anvils of the smiths, who had been left on the beacon throughout the day, which afforded a guide for the boats, a landing could not have been attempted this evening, especially with so large a company of artificers. This circumstance confirmed the writer’s opinion with regard to the propriety of connecting large bells to be rung with machinery in the lighthouse, to be tolled day and night during the continuance of foggy weather, by which the mariner may be forewarned of too near an approach to the rock, while every distant object is obscured in the mist.”