The talus wall for protecting the seaward side of the harbour, has about 60 feet of its foundation laid in a depth of water varying at low spring-tides from 18 inches to 3¹⁄₂ feet. The mode of its construction, as already stated, is shewn in [Plate XI.] It is surmounted by a strong parapet of rustic masonry of Mull granite, and is altogether a most substantial piece of work.
The idea of a tide-basin with boom-gates facing the breach of Atlantic waves is somewhat novel and was not very hastily entertained by me at first; but the most complete success has attended the plan. During my occasional visits to the works in the course of the summer 1843, our attention had been often occupied with considering the probability of the sand shutting up the basin; and as a single tide during heavy winds from the N.W., made great changes on the appearance of the beach, we feared that the vessel might often be imprisoned within the boomgates by a bank of sand heaped against them by the sea. To such an extent did the accumulation go before the harbour was fully opened, that on many occasions there was not water for a rowboat to pass between the boom-heads even at the highest spring-tides. The only remedy for such an evil, was obviously to attempt some mode of artificial scouring; and for that purpose, it was proposed to divert several small streams which run from Ben Hynish and the neighbouring hills through the grounds at Hynish, into one feeder, and pen them up in a pond, so as to afford the means of scouring the entrance to the basin from the incumbrance of the loose sand which might choke it. Those streams were repeatedly gauged during the summer and were found to deliver from 13 to 50 cubic feet of water per minute, according to the state of the weather,—a supply which seemed ample for the purpose in view. The sand at Hynish is of a light nature and is easily acted on by currents of very feeble power. It consists of comminuted shells and requires about 25¹⁄₂ cubic feet to make a ton, instead of 24 feet, which is the common allowance for silicious sand. The leave of the Duke of Argyll and also of the Farmer at Hynish, having been obtained, various cuts were made and the stream was diverted into a pond capable of containing about 175,000 cubic feet and provided with a waste-weir and with sluices for opening the communication between the pond and the scouring tunnel, from which the water flows in a stream of about 9 square feet of area, at the rate of about 260 feet per minute for a period of 1¹⁄₄ hour. The operation of scouring is performed at low water and is generally found quite sufficient for the purpose of clearing a passage down to the bare rock in a single tide. Nothing can be more satisfactory than to witness the effect of that process in opening the entrance to a basin apparently inaccessible; and but for such an arrangement, the dock must have remained permanently choked with sand and sea-weed. The position of the various works is marked in [Plate X.], which shews the ground at Hynish.
On the side of the dock stands a crane, which is used for various purposes connected with the shipment and discharging of materials. It also serves for raising the booms, by means of a double hook, which can be attached to the chain and which embraces the pegs in the centre of each boom, shewn in [Plate XI.] The two tiers of booms are firmly lashed down by means of chains passing through ring-bolts in the manner shewn in the section ([Plate XI.]), so as to prevent their rising with the tide.
The necessity of providing somewhere in the neighbouring island of Tyree for the proper accommodation of the vessel which was to wait upon the Lighthouse (if it could ever have been a matter of doubt), was abundantly demonstrated by the experience of 1843, and more especially by that of the months of November and December. Owing to the shortness of the day and the distance of any place of shelter from the Skerryvore, together with the difficulty of landing on the Rock and the extreme variableness and uncertainty of the climate, the Regent Tender, although constantly waiting on the coast and making trials on every occasion that seemed to offer any prospect of success, could not effect any communication with the people who had been left on the Rock, during a period of no less than seven long weeks. The poor seamen who were living in the Barrack passed that time most drearily, for not only had their clothes been literally worn to rags, but they suffered the want of many things dearer to them than clothes, and amongst others of tobacco, the failure of the supply of which they had despondingly recorded in chalk on the walls of their prison-house, with the date of the occurrence! Unless, therefore, the vessel had been stationed near the rock, the few casual and uncertain opportunities which occur at intervals, during the short days of winter, would often have been lost, and the future maintenance of the Light rendered excessively precarious. The experience of subsequent years, during which the relief of the Light-keepers has been kept up with considerable regularity, shews that the small Harbour at Hynish forms a most important integral part of the Establishment of Skerryvore, than which I believe no Lighthouse on the coast is more comfortable as a residence.
In connection with the Harbour at Hynish, I naturally notice the erection of a Bo Pheg Beacon. Beacon on a rock called Bo Pheg, which is dry only at low water of spring tides. It lies about one mile NE. from Hynish Point, (See [Plates II.] and [X.]) right in the track of the Tender in its passage to and from the Lighthouse. From the great difficulty of landing on that small rock, over which the sea almost continually breaks, even in very fine weather, the shortness of the time during which the men could remain at work, and the want of room on its irregular surface of about 16 yards square, the erection of a beacon proved to be a work of great difficulty. The Beacon consisted of an open frame-work of iron, (somewhat on the same plan as that which is described in the Appendix) and calculated to offer little opposition to the free passage of the waves; but before all the fixtures could be completed, the heavy storms of the winter of 1844, acting on its unfinished base (the bats of which were only partially secured), destroyed it piecemeal, at a season when no landing could be effected, nor any effort made to save almost any part of it from the sea. In the ensuing summer, a second Beacon, consisting of a hollow cone, composed of iron plates, united together by strong flanges and attached to the rock by webbed flanges round its base with strong bats passing through them, was fixed down to the rock; and in order to increase its weight, the interior was filled with concrete gravel. That structure also has since yielded to the force of the waves, after giving slight indications of movement, an effect which I attribute chiefly to the smallness of the base, which the narrow limits of the rock unhappily prescribe.
Another necessary part of the Establishment at Hynish, was the provision of Lightkeepers’ and Seamen’s House. dwelling-houses for the families of the Lightkeepers and Seamen and of Storehouses of various kinds. Those were partly built on purpose and partly consisted of altered forms of the buildings which had been found necessary as barracks for workmen and stores for materials, during the progress of the works.
On landing on the Rock, on the 29th of March 1843, the Resident Engineer had the satisfaction of finding the whole building perfectly water-tight and saw not the slightest trace of a defective joint. Concluding works on the Rock, such as pointing, &c. The outside joints of the building were therefore carefully “ripped,” and repointed with mortar, composed of equal parts of Halkin lime and Pozzolano. That operation, from the difficulty of employing many men, where suspended scaffolds were necessary and from the care with which it requires to be executed, occupied a great deal of time.
Another tedious operation was the Interior fittings of the Tower. fitting up of the interior of the Tower with wainscot lining and forming the various stories into apartments separate from the staircase. Much work was also expended in providing the fire-places with proper flues, in fitting up water tanks, coal stores, and oil tanks, and also in conveying the air-tubes between the Lightroom and the several apartments by which the signal bells are rung for summoning the keepers to mount guard. The keeper on duty is, by the rules of the Service, forbidden, under penalty of instant dismissal, to leave the Light-room, on any pretext, until relieved by the next who mounts guard, and who is summoned by means of a bell placed inside his cot or sleeping berth, which is rung by means of a small piston, propelled by simply blowing into a mouth-piece in the Light-room. The keeper in bed answers this signal by a “counter-blast,” which rings another bell in the Light-room, and informs the keeper there that his signal has been heard and will be obeyed.
Arrangement of the several apartments. The general arrangement of the Tower, may be seen in the Section [Plate VIII.]; and the details of its subdivision are very similar to those shewn in Plate XVI. of my Father’s Account of the Bell Rock Lighthouse. The ascent to the outside door is by a ladder or trap of gun metal, 26 feet high. The first apartment on the level of the entrance door, is chiefly appropriated to the reception of iron water-tanks, capable of holding a supply of 1251 gallons. The next story is set aside for coals, which are stowed in large iron boxes. The third apartment is a workshop; the fourth is the provision store; and the fifth is the kitchen. Above are two stories, each divided into two sleeping apartments, for the four Light-keepers. Over them is the room for the Visiting Officers; then follows the oil store, and lastly comes the Lightroom, making in all twelve apartments. The nearness of the oil store to the Lightroom is a great convenience to the Keepers, who are thus saved the trouble of carrying the daily supply of oil to the Lightroom, up a long flight of steps. The passage from story to story is by oaken trap ladders, passing through hatches in each floor and partitioned off from each apartment in order to prevent accidents and to check cold draughts.
Lightroom Apparatus, and first exhibition of the Light. The light of Skerryvore was exhibited to the mariner on the night of the 1st February 1844, in terms of the [Statutory Notice], which will be found in the Appendix. The light is revolving, appearing in its brightest state once in every minute of time. It is elevated 150 feet above the sea, and is well seen as far as the curvature of the earth permits; it is also frequently seen as a brilliant light from the high land of Barra, a distance of 38 miles. The apparatus consists of eight annular lenses (of the first order, in the system of Augustin Fresnel), of 36·22 inches focal distance, revolving round a lamp with four concentric wicks, and producing a bright blaze when each lens passes between the lamp and the eye of a distant observer. Above those lenses are placed eight pyramidal lenses of 19·68 inches focal distance, inclined at 50° with the horizon and combined with eight plane mirrors, inclined in the opposite direction at 50° with the horizon. By this arrangement, that part of the light from the lamp which would otherwise escape uselessly beyond the great lenses, upwards into the sky, being parallelized in its passage through the smaller lenses and falling on the mirrors, is finally projected forwards in horizontal beams, so as to aid the effect of the light. Those lenses and mirrors, however, instead of having their axes in the same vertical plane with the axes of the principal lenses, are inclined about 7° horizontally to the right hand, and by that deviation produce small premonitory blazes, which, blending with the beams of the larger lenses, tend in some measure to lengthen the duration of the impression on the eye. So far the apparatus of the Skerryvore Lighthouse is identical in its general arrangements with that of the Tour de Corduan, and differs only in the superior workmanship of the lenses and the machinery, which the experience of more than twenty years has brought about, since Fresnel designed that light in 1822. Instead, however, of employing curved mirrors, as has been done at Corduan, to collect the light which would otherwise escape below the lenses and, at the same time, to send it to the horizon, I determined to put in practice a plan which I had long contemplated, of placing totally reflecting zones below the lenses, similar in construction to the zones of the small Harbour Light Apparatus of the fourth order, which was also invented by Fresnel. This was finally carried into effect, agreeably to the design of M. Leonor Fresnel, his brother, with whom I had corresponded on the subject. In the subsequent pages of this volume, I intend to make some observations explanatory of the principles and arrangement of the various optical instruments employed in Lighthouses; and as that will afford me a more convenient opportunity of describing the nature and properties of the totally reflecting zones, I shall forbear in this place to enter into further details as to the construction or action of the apparatus at the Skerryvore. It is right, however, that I should mention here that the lenses, mirrors and zones are from the works of M. François of Paris, whose name I shall afterwards have occasion to notice; and that the machinery was constructed to my entire satisfaction, and in a manner worthy of his reputation as a mechanician, by Mr John Milne of Edinburgh.