Mr Stevenson, to whose merit I am happy to bear ample testimony, has been indefatigable in obtaining information respecting this Rock, and he has made a model of a stone Light-house, nearly resembling that of the Edystone, in which he has proposed various ingenious methods of constructing the work, by way of facilitating the operations. I own, however, after considering these in the fullest manner I have been able, and comparing them with the construction of Mr Smeaton’s, I mean in the building, and also that there is undoubted proofs of the stability of the Edystone, I am inclined to give it the preference. No doubt some methods different from the Edystone will require to be put in practice for the foundation; but its general construction, in my opinion, renders it as strong as can well be conceived,—in fact, it may be looked upon as a solid mass of rock. Viewing the matter, therefore, in this light, it will be unnecessary for me to accompany this Report with the design of a Light-house. It will be time enough to make such a design, when the Commissioners shall be in a situation to give orders for the erection, and then I have no doubt Mr Stevenson will furnish much valuable matter towards the perfecting of it.
The total height of the Edystone Light-house, from the lower course of stones on the rock to the top of the platform or balcony-floor, is about 70 feet; from thence to the bottom of the iron-frame of the lantern about 6 feet 9 inches; and the lantern itself is about 8 feet 3 inches; so that the total height to the eve of the cupola is about 84 feet 6 inches. Now, as the Bell Rock lies so much lower than that of the Edystone, I think the height of the shaft or tower of the Light-house should not be less than 80 feet, or, perhaps, a little more, say 85 feet; so that the cupola will, in this case, be about 100 feet above the surface of the rock. With such a height of Light-house as is here proposed, I would advise that the diameter of the base should be greater, and as it is less surrounded by such an extent of rock, it will give facility to the gradual diminution of the effects of the waves breaking upon it; will render the fabric more steady, and, as it will diminish quickly, no great additional surface will be presented to the sea.
The floor of the lower room, i. e. the height of the solid part of the Light-house, I would propose to be about 50 feet, and from thence to the top of the platform 35 feet, making a total height, from the rock to the platform or gallery, of 85 feet. As to the lantern itself, I need say little on that head, as lanterns for light-houses have, of late years, been greatly improved, as well as the lights. The substitution of lamps with reflectors, in place of coal or candle lights, has been found of the greatest advantage to the mariner; and it is not unlikely, from what I have been lately made acquainted with, that the substitution of the hydrogen gas in place of lamps, will not only prove a much cheaper, but a better light than even lamps. I am told that it will not cost above one-eighth of the price of oil. The kind of light to be used is also a matter of consideration, for unless lights are so constructed as to enable the mariner to distinguish between one and another, he may be apt to mistake his situation; but that also can be easily arranged, when this part of the subject comes to require consideration. The new light on the Skerries in Orkney is a revolving one; perhaps a similar one may also be judged advisable here, as, if the Light-house on the Island of May was to be fitted up with reflectors in the usual manner, it would not always be easy to distinguish this from the Cape Rock, unless one of them was to be made a revolving, or the lights to be placed in different situations of the house.
A Light-house has, of late years, been built on the South Rock, near the mouth of Loch Strangford, on the coast of Ireland. This Light-house was begun on the 11th of June 1795, and completed the 25th March 1797. It is 30 feet diameter at the base, and about 15½ feet just below the balcony floor. It is 56 feet high from the rock to the platform or balcony floor, and its shape is the frustum of a cone. It is built of granite from the Mountains of Morne; and the lantern, from the platform to the cupola, is about 12 feet high, and 10 feet wide. The light is a revolving one, and lighted by 10 lamps with reflectors, 3 in the upper course, 3 in the lower course, and 4 in the middle, and makes a revolution in five minutes. This distinguishes it from the Copland lights.
The rock on which this Light-house stands is about 400 yards long, and about 100 wide, and is covered about 18 inches deep at high-water, ordinary spring-tides. The rock is composed of beds of schistus, intermixed with beds of a kind of indurated clay, which are wearing fast away by the washing of the sea; and, unless some speedy and effectual means are taken to secure it, this Light-house will not be of long duration. It has cost about L. 22,000, and it is said that L. 7000 more will be required to secure the rock from washing away. I will not take upon me to say that this sum will be sufficient for the purpose; but it seems to me that it will not be a very difficult matter to secure the rock, if proper means are taken. The channel is here narrow, and the seas cannot be very heavy; indeed Macculloch the Light-house keeper informed me, that they seldom rise above the first landing, which is only about 27 feet from the top of the rock.
In the construction of a Light-house at the Cape Rock, great care will be necessary in choosing stone of the most durable quality, fit to resist the effects of the waves. For this purpose, I examined the rocks lying along the shore nearest adjoining the Inch Cape Rock, but found none of a very durable quality; most of it is a red freestone, softer than the rock itself, which has been much worn away by the wash of the sea, and therefore by no means fit for the exterior work of such a building; and there does not appear to be any fit for that purpose nearer than Kingoodie, about three or four miles from Dundee. This stone is a hard millstone-grit, of an excellent quality; very hard to work, but can be raised in blocks of any size and thickness required. It therefore appears to me to be most fit for the exterior work of a Light-house to be built on the Cape Rock; but as the price the proprietor asks for it is very high, it becomes a question whether the solid part of the building may not be done with the stone from near Arbroath, which, although not fit for exterior work, is yet of a pretty strong quality, and might be used in the solid part of the building, not exposed to the weather or wash of the sea: Or, it may be a question, whether the saving that would arise from using the stone near Arbroath, is a consideration, when put in competition with the superior strength and specific gravity of the Kingoodie stone.
Granite is also a stone that will resist the waves without wearing, and it is therefore a matter of consideration, whether granite stone might not be had from Peterhead or Aberdeen for this purpose. Granite, it is true, cannot conveniently be had in such large blocks as the Kingoodie stone, but it may be had in blocks sufficiently large to answer the purpose, and, if well dove-tailed, and properly cemented together, the whole may be made to act as one solid body of rock.
As to the expence of a Light-house in such a situation, it is not a very easy matter to form any thing like a correct calculation. So much depends on weather, on the untoward circumstances that may probably happen while the work is in hand, that they baffle even the most experienced artist to make the proper allowances. The price and quantity of materials is by no means difficult to ascertain; but the expence of putting them together must be more a matter of guess than of correct and well founded calculation. I have, however, computed the expence that such a work ought to cost, and have made every allowance for contingencies, from my own experience of works in the sea, and from what I have been able to collect from the experience of others, in which, I think, I have made a very full allowance for contingencies, and the cost amounts, by my estimate, to L. 41,844, but I will say L. 42,000, and, I trust, if ever the work is executed, and done with judgment, it will not exceed that sum.
I have gone on the supposition, that the outside is to be made of Kingoodie stone, and the hearting of stone from near Arbroath. I am, Gentlemen, your most humble servant,