HISTORY OK ENGINEERING.

Book I.

338

sage, ami the face built up above high-water mark ; by which the passage to the harbourwould be widened to 5 yards, and in the narrowest part from -15 to CO feet. The seawould also be prevented by this means from breaking upon the sloping rocks, and the newpier being carried up sufficiently above high water mark, by means of rope, vessels mightbe towed when they did not come in with sufficient fresh way to keep them clear of theentry.

He also advised that a pier should be carried out upon the ledge of rocks which at lowwater were dry, on the south-east side of the entry from the north angle of the present pierto the Beacon rock, w’hich would defend the passage from the surge of the sea, and serve asa help, by its projection, to the throwing a rope on board a ship on the larboard side. Asthe construction of a pier that would resist the full stroke of the sea ought to be of greatstrength, and consequently its expense might be objected to, he devised a gangway, toextend as far as the Beacon rock, where men could give the necessary assistance by heavinga rope on board, which might be executed at a moderate cost.

This structure was proposed to be composed of few materials, for it was found that itwas generally better to elude the force of the sea than to resist it, and the less matter opposedto its action the better, provided that be securely and permanently fixed. The rocks were tobe bored by a jumper, 1£ inch diameter ; to these the eye-bolts were to be forged, a littletapering, and larger than the holes, so that they might be driven tight, by means of an ironmaul; and if they were found too small, strips of iron plate were to be introduced, andin a short time the rust would prevent their being moved or drawn out.

As this proposed pier would receive the full stroke of the sea, when the wind wassouth-easterly, it was not only necessary that it should be built very firmly, but in such amanner that the ordinary seas should not break over it; he therefore proposed that itshould be raised 9 feet above high water at spring tides, which is 22 feet above the lowwater line at the pier head, and that it should have an inclination, as it continued fromthe south-west towards the land. Such a height would carry it considerably above therocks, where it was built, and therefore, instead of so large a quantity of backings as wouldbe necessary to make the whole good to that level with the land, he proposed it to bebuilt upon the other side.

The rocks at the foot of the pier were to be removed before the pier was built, andwhere the pier was founded, the rocks were to be cut off level, so that the lower course ofstone had a proper bearing.

Dunbar had its harbour originally at Belhaven, some distance from the town, thoughwithin its liberties.

Cromwell began the eastern pier of the present harbour, and some years afterwards thelatter was deepened by taking away, Over its whole surface, 8 feet of the solid rock. Afterthis work of great labour and expense, a new pier was built. Between the harbour andthe fortress are some basaltic rocks which dip towards the south, and are crystallised intoeither triangles or hexagonal figures like those at the Giant’s Causeway.

Leith , the port of Edinburgh , stands at the mouth of a small river of that name; theharbour at neap tides has about 8 feet water, and at high spring tides nearly 16 feet.There is a communication with Edinburgh by a causeway nearly two miles in length, and50 feet in breadth. In 1777 great improvements were made in the harbour; the pier wascontinued to a considerable distance into the sea; a quay, basin, and docks, were at thesame time constructed at a great expense; and in 1801, Mr. Rennie commenced a newdock, since which others have been suggested and partly carried out, and to raise thevessels there arc slips with iron ways; the ship is supported by a cradle which runs uponwheels.

Adjoining to Edinburgh , on the north, is the Frith of Forth, or ancient Bodotria, whichis from five to seven miles in breadth; the largest of its bays is that of Musselburgh,which advances several miles to the south of the village, whilst the harbour of Leithoccupies the angle or peninsula formed by the line of the Frith of Forth on the north, andthe Bay of Musselburgh on the east.

The trade of Leith is considerable, and one of the docks for building ships formed at theentrance of the new basin presents three quadruple rows of steps, 29 inches high, and11 inches in breadth, which gives a total depth of 21 feet. The division of the rows ismarked by a bench 20 inches in breadth. The breadth of the dock at bottom is 44 feet,and the entrance to it is about 35 feet; the entire breadth at the top or level of the groundis 70 feet.

An iron bridge, 12 feet 6 inches in width, composed of 6 ribs, and which cost 1365/., isplaced over the entrance to the basin.

On the south side of the Forth, at Newhaven, is the chain pier constructed by CaptainBrown.

Leith is protected by a fort, which was considerably strengthened by Cromwell; sincewhose time a battery has been constructed on an eminence behind the docks, which extendsto Newhaven; this is surrounded by an intrenchment, and defended by bastions. In the