Chap. VIII-

BRITAIN.

S3 5

The frames of all the sluices arc made of cast-iron, as arc the sluice gates.

There are also some admirable cast-iron turning bridges, 45 feet 6 inches span, which workupon pivots and conical rollers, about 9 inches in diameter; each leaf of these bridges is madeto open by a sector rack, attached to the tail plate of each leaf, having a pinion with a spurand pinion, working into each other.

Sunderland , 20 miles south-east of the town of Berwick-upon-Tweed, occupies the rightbank of the mouth of the Wear, and Wearmouth the other, and the two towns are unitedby an iron bridge of 236 feet span, and 98 feet from the underside to the level of highwater.

The Wear is not navigable to Durham , as it is not swelled by many tributary streams.

From Sunderland bridge to the sea, a distance of a mile, the Wear forms an extensivedock, which is full of vessels engaged in the extensive coal trade carried on here. This iskept constantly open by the dredging machine, and there is a floating dock formed withconvex gates; where the river empties itself into the ocean, the passage is confined by twopiers, and from the force with which the tidal water mounts, there is never any obstructionat the mouth. The piers are composed of stone, laid in short horizontal courses, terminatedat equal intervals by vertical timbers, so that if any part is broken through and carriedaway, it can be easily repaired.

At the end of the southern pier is a lighthouse, built of timber, and at the distance of90 feet from the point of the north pier stands the great lighthouse.

The entrance to the harbour lies east-north-east; and on the eastern side is a ledge ofrocks, which extends a quarter of a mile to seaward; this is covered at high water; theharbour is sheltered on all sides, except from the north-east.

The tide ebbs about 100 yards from the head of the north pier, and the harl>our is dry atlow water; spring tides rise about 18 feet; between the jetties at the entrance there is Cfeet at low water; neap tides rise only 9 feet, at which time there is only 6 or 7 feetwater in the harbour.

Removal of the Lighthouse at Sunderland. — This building, which is octagonal on theplan, is of stone; its height is 62 feet 2 inches from the base to the cornice, and thelantern above was 1G feet, making a total height of 76 feet 2 inches. Its breadth at thebase was 15 feet, and it diminished to 8 feet 6 inches. The lighthouse was erected in1802, at an expense of 1400 pounds sterling; and in consequence of a breach made bythe sea in the year 1841, it was required to be moved to a foundation prepared to receive it,a distance of 447 feet.

This operation was performed very successfully, in the following manner : —holes werecut through the stone walls on the north and south sides of the building, through whichwere passed six timbers, intended to be framed into a temporary platform. Where thesemain timbers came in contact with the masonry, they had spread over them a sheet of lead,to prevent their being unequally acted upon. Screws were then placed under thesetimbers, and they were forced to a bearing; after this upright timbers were introducedunder them, and the screws were taken away. Four other timbers were then introduced,laid parallel to the first, which were screwed up and supported in a similar manner.

A hole was then cut on the eastern side, opposite the door, and through it were intro-duced two transverse timbers, which were firmly screwed to the others, and when shoredup, the screws under them were taken away.

Timbers were then introduced with rails fixed to them ; those in the centre, below theupper beams, were first fixed, and then bedded on the stone pavement around; thesheave balks to each were then threaded through the building, wedged to the timbersabove, as well as to the rails below, by a scries of wedges. The other rails and sheavebalks were then similarly fixed underneath each timber, and when all the wheels werebrought to a proper bearing, the stone work, which had been allowed to remain at fourangles of the building, was cut away, and then two other timbers were introduced andsecured.

The octagonal lighthouse had a three-inch plank from bottom to top laid against it ateach angle, and these were hooped round with five iron hoops 2J inches broad, and g inchthick ; ropes and wedges were employed as well at regular distances, the whole madeto embrace the building, and by means of screws were drawn closely up to the uprightplanks.

Under the cornice a hole was cut on each of the eight sides, where the walls were 10inches in thickness; through these were pushed horizontal timbers from the inside,and these were drawn back until they met in the centre. Iron plates covered the jointsabove and below the timbers, and screwed bolts passed through both.

This upper timber platform was connected to that below by a large chain, whichpassed round a strong bar of iron at the top, and another at the bottom, which wastightened by a screw’. Eight upright timbers, a foot square, were tenoned into the hori-zontal timbers under the cornice, and brought close to the outer wall of the building,at the base, where they were secured by stirrup straps and bolts; these uprights were