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.”
Following out this subject, Mr. Stevenson caused observations to be made at the Calf of Man—a small island at the south of the Isle of Man, and separated from the main island by a narrow “sound.” The place is noted for its fogs, on which Mr. Stevenson says:—
“I sent Mr. Macurich, a shipmaster in the lighthouse service, to the Calf of Man, with directions to reside there, and make monthly returns of the state of the weather, agreeably to a printed form. During his stay of seven months, it appears upon the whole that the fog rested only twice upon the highest land of the Calf Island, while it cleared partially below. On one of these occasions I was on board of the lighthouse yacht, then at anchor off the island, when the fog was for a time general; and as the weather became clear, I observed that it first disappeared upon the lower parts of the island, and that in half an hour the whole of the Calf was seen. In the monthly returns made by Mr. Macurich, the Calf island is represented as often perfectly free of fog, while the higher parts of the opposite mainland of the Isle of Man were hid in mist. To account for this, it may be noticed that the mass of matter in the Calf Island is much less, and the land is also much lower than in the main island. Part of this effect may also be ascribed to the rapidity of the tides, which create a current of wind, particularly in the narrow channel between the main and Calf islands, which have a direct tendency to clear away the fog, as I have observed at the Skerries in the Pentland Firth, and in similar situations on different parts of the coast, where rapid currents prevail.”
These extracts are given to show the attention Mr. Stevenson gave to the subject of fogs, which, as already noticed, led him to recommend the horn, the instrument now so much used in giving signals to the mariner.
Akin to this may be mentioned his expression of regret that no means existed for determining the force of the wind, as noticed in the following paragraph:—
“We cannot enough regret the want of an efficient anemometer, or instrument for measuring the force of the wind. Indeed, we hardly know any desideratum of more universal interest, for, notwithstanding the labours of Lind and others on this subject, from the want of a proper scale we are still groping in the dark with the use of such indefinite terms as ‘light airs inclining to calm,’ ‘fresh breezes,’ ‘fresh gales,’ ‘hard gales,’ and ‘very hard gales;’ for it rarely happens that the sailor will admit the term ‘storm’ into his nomenclature.”