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HISTORY OF ENGINEERING.

Book I.

this was highly necessary, as the several courses were dovetailed together, so as to formone mass, from the centre to the circumference. The stones were all bored for trenails ofoak and joggles of stone, in the same way as practised at the Eddystone.

The lighthouse is 42 feet in diameter at the base, and 13 feet at the top. The partconstructed in masonry is 100 feet in height, and including the light room it is 115 feet;the mortar used was sand, pulverised lime, and puzzolana, in equal quantities. Theascent from the rock to the top of the solid part, or lowest 30 feet, is by a trap ladder; andfrom the entrance doorway a circular staircase leads to the first apartment, which con-tains the fuel, water, and stores. The other apartments are approached by wooden stairs;they consist of a light store-room, a kitchen, bed-room, library, and light room; in all, sixstories.

The three lower rooms have two windows each, and the upper four, all glazed with thickplate-glass, and guarded on the outside from the violence of the spray of the sea by woodenshutters. The light-room, which is 88 feet above the medium level of the tide, has aroundit a projecting balcony with an iron railing; the interior dimensions of this octagonalroom is 12 feet in diameter, and 15 feet in height. It is framed of cast-iron, and glazedwith plate-glass, each plate being 30 by 27 inches; it is terminated with a dome roof witha circular ball; and the light used is from oil, with Argand burners, placed in the focusof silver plated reflectors, hollowed to the parabolic curve by hammering only. Thesereflectors measure 24 inches across, and the light is so powerful that it may be seen, whenthe atmosphere is clear, 6 or 7 leagues.

The above lighthouse is the most important in the northern division; the others, erectedon the points or promontories connected with the main land, or upon the islands on thecoast of Scotland, including the Isle of Man , are more rudely constructed. That at theMull of Kintyre in Argyleshire, almost inaccessible by sea, from the rocky and precipitousstate of the coast, stands 240 feet above the level of the sea, and so difficult is the approach,that the stores cannot be landed nearer than at a spot six miles distant.

The Pentland Skerries in Orkney consist of two islands surrounded by a reef of sunkenrock : one of these is about 15 acres, and has been entirely stripped of its soil by the seawashing over it; the other, called the Great Skerry, contains 75 acres: on both are light-houses, not, however, remarkable for their construction.

The methods adopted till lately on these coasts for distinguishing one light from another,where the distance and bearing by the compass were not sufficiently marked, was effectedby double and single stationary lights, a method expensive and not to be relied on as aguide to the navigator, from the frequency with which they were made to occur on thecoast in many districts; the revolving light has been substituted to great advantage, whichvaries its character by the different tints given to the glass.

These several lighthouses arc under the direction of a board of commissioners, exceptthose of the Tay, which come under the management of the Trinity House; the Com-missioners of the Northern Lighthouses were established about the year 1780, and six yearsafterwards a bill was brought before parliament, to enable them to erect several newbuildings on the coast, which had become frequented by the vessels engaged in the fisheries.

Arbroath , which stands on the river Brothwick, has a small harbour of a rectangularform, defended from the sea by a wall of hewn stone on the north, and by a pier on thesouth side. The entrance is closed by a floating boom, which slides between a double rowof piles, and is made to ascend by a capstan.

Montrose is situated in a fine bay, and at its quay vessels of 400 tons burthen ride inperfect security, sheltered on the north by the town, and on the south by lofty hills.

The town is situated on the north bank of the South Esk, a torrent which descends withconsiderable violence from the Grampian Hills, and forms a vast bay, near where it dis-gorges itself into the sea; over the entrance, which is very narrow, is the bridge leading toMontrose, 244 yards in length ; the piers are of timber, and have been considerably injuredby the ravages of the worms, of the genus Oniscus, particularly on the side towards the sea.An opening is formed in the middle of the bridge, by lifting a portion to admit vessels intothe bay.

At the mouth of the river on one side are dangerous rocks, and on the other a shallowbottom of sand, without consistence, extending several miles into the bay, which, by aneasterly wind, is blown into the harbour, and again removed by the Esk, as the tide ebbs,driving it outwards.

The North Esk runs parallel with the South Esk, and empties itself a little to the northof Montrose; it is crossed by the stone bridge of Money Kirk, of four arches, built at thecost of 10,000/., after the design of Mr. Stevenson.

Gourdon is a small fishing town, two miles south of Bervie, in the county of Kincardine-shire . Bervie, the ancient port on the river of that name, has an elegant bridge, on theabutments of which is built the town hall. King David , in 1342, made it a royal town orborough, in consequence of the reception given him by the inhabitants after a violent storm.