Discussion. The Dhu Heartach Lighthouse.

Abstract

remarked that the Messrs. Stevenson were to be congratulated for having completed the work without loss of life or limb to any of the persons employed, and also for having adopted granite for the tower. KO doubt the tower might have becn conBtructed with wrought iron or cast iron, but, in doing so, little reduction would have been effected in the cost, while an annual outlay would have been involved for the preservation of the work, and there would have been a limit to its duration. The Author had furnished some interesting particulars relative to the heavy seas experienced a t Dhu Heartach. The position of the rock and the nature of the soundings seaward were doubtless sufficient to account for heavy seas, but he did not consider there was evidence to show that heavier seas occurred there than at the Bishop or the Wolf rocks on the west coast of England, as might be expected by comparing the soundings. On the north-west, or most exposed side of the Bishop, a t a distance of 4 miles, there was a depth of 50 fathoms, gradually shoaling to 30 fathoms close to the rock, which had a gradient to the westward of about l in 1. These were favourable conditions for heavy seas, and for the concentration of their force upon the building. Both at the Bishop and at the Wolf, where the soundings and gradients of the rock were similar, heavy seas rose several feet higher than the building before cresting; but, fortunately, they crested after they had passed the building.Such seas fell and were spent a t about a cable's length from the tower. The destruction of the iron pile lighthouse first erected on the Bishop was due to unbroken seas striking the dwelling, the floor of which was 85 feet above high water and the surface of the rock. During a storm on the 30th of January, 1860, the fog bell, weighing 3 cwt., was torn from the bracket, on the lee side of the lantern gallery, 100 feet above high water; and during a storm in the winter of 1874-5 the heaviest seas experienced since the completion of the lighthouse in 1858 were encountered. On this occasion the tremor of the building was so great as to cause articles to leave the shelves. On his recommendation the building had since been strengthened by strong internal vertical and radiating ties of wrought iron secured to the walls and floors. At the Wolf, before the erection of the lighthouse, there was evidence of the enormous force of the heavy seas falling on it, in the breaking off, on three occasions, of the masts of the beacon-one of English oak and two of wrought iron, the last being 9 inches in diameter.