Chap. VIII.

BRITAIN.

401

Hie new pier is formed half a mile further to the east, or nearer to Dalkey , at the com-mencement of a rocky tract, called Codling Rocks, to the westward of which, within shelterof the pier, the bottom is of tine sand.

The first stone of the new pier was laid in 1817; it extends 2800 feet, and has four arms,the first running directly from the shore, to the distance of 1500 feet, in a north-east direc-tion ; the next continues north, the third north-west, and the fourth west, each 500 feet inlength. The base of the pier is about 200 feet in breadth, terminating in a perpendicularface towards the harbour, and battering towards the sea ; on the top runs a quay, 50 feet inwidth, which is protected by a parapet wall, 8 feet high. At the extremity is placed thelighthouse. The depth of water at the pier-head is 24 feet at the lowest springs, which atall times is sufficient to shelter large trading vessels and ships of war. The estimate forthe completion of these works, as laid before Parliament , was 505,000/.

The Harbour of Cork, 8 miles from the city, is one of the most capacious and secure inthe British empire. The outward entrance is barely half a league, but having passed abank, called the Turbot, on which there is 30 feet water, the entrance narrows to half a mile.In this great basin lie the two islands of Spike and Halbowlin, placed as it were to formbulwarks against the winds and the ocean; so that vessels may lie in the harbour land-locked.Extensive barracks and a dockyard are formed on these islands, which are distant fromDublin about 125 miles.

Jersey Harbour _St. Helliers, when Smeaton reported upon it in 1788, had a pier, which

he denominated a screen , and he suggested some improvements, which have since been par-tially carried into effect; but he observed, “ that no small harbour could be made quiet,

Fig. 399.

JERSEY BARBOUR,

for the magnitude of the waves are supposed the same to all, and the necessary width of themouth for a ship to enter the same : seas, then, that will inevitably sweep round the heads,will affect a smaller harbour more than a large one, though of similar constructions;for the effect of the waves in disturbing a harbour is greater in proportion as the linealwidth of the mouth is to the whole area of the harbour : for this reason St. Helliers mustalways be defective. Another circumstance tends to render such a harbour unquiet, andthat is, when they are bounded by walls. The waves of the sea follow the laws of the pen-dulum, which, when once set vibrating, would never cease if not stopped by friction and theresistance of the air. The same would happen to the libration of the water if there werenothing to stop it; for, meeting with walls and objects comparatively smooth, the wavesare not destroyed, but reflected into another direction, and from that into another, till theyare gradually dispelled by friction. The speediest way by which waves are destroyed(that is, by friction,) is by forming a surf, and breaking upon a sloping beach, sand, orrocks, in which the harbour of St. Helliers is defective.”

The catch pier, suggested by this engineer, extended into the harbour 550 feet, and thespring-tides rise here upwards of 40 feet, but the neaps run very short.

There not being in the inner harbour any backwater to scour away the sand, it accumu-lates in large quantities, and Smeaton advised the making of arches through the pier, as waspractised by the Romans, and which had the effect of disturbing the deposit, which waspartly carried out to sea on the retreat of the tide.

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