336
HISTORY OF ENGINEERING.
Book I.
united by three tiers of chock pieces ; three iron straps passed round these as well as theuprights, and the whole screwed tightly together.
After this, raking braces were added, and the whole firmly bound together ; then diagonalbraces, to prevent the timbers from springing or twisting.
When the whole of these works was completed, five pulling screws were attachedto the glacis of the pier, and the chains were fastened to them ; 24 men were employed toturn these screws, four forcing screws, worked by three men at each, being appliedbehind the cradle to help propel. The total number of men employed amounted to fifty.
The platform or cradle that carried the whole weight, which was 333 tons, was supportedon 144 wheels, which moved on eight parallel lines of rails.
The cradle timbers were of American oak, and all the rest was Memel ; the cast-ironrails upon which the wheels moved were laid upon a plank of African oak inches inthickness.
There were employed, during the operation at the winches, 18 men, and their powermay be estimated as equal to 562^ pounds. The radius of the handles of the winches was14 inches, worked by a cog-wheel of 4^ inches diameter, turning a spur-wheel of 30 inches;and a barrel of 10 inches in diameter. The additional power of the two-fold and three-fold sheave blocks, made the whole power of the 18 men equal to 52,480 pounds, whilst thegross weight was 757,120 pounds.
The speed with which the whole was moved was about 84 feet per hour, when atthe quickest; and the time occupied to move the whole distance was 13 hours 24minutes.
The foundations prepared to receive the lighthouse after its removal were formed ofsolid blocks of stone, and when it had arrived over its destined position, the timber uprightswere again wedged under its cradles, and the various sheaves and railway timbers drawnout. The masons then underpinned it by degrees, striking the upright supports as thebuilding had obtained its proper bearing.
Mortar, composed of blue lias lime, sand, and puzzolana, was made use of, and greatcare was taken to pin up the last course; a sheet of lead being introduced to equalise thepressure.
Since its completion the works have stood remarkably well, and no settlement has takenplace. The accomplishment of so arduous and novel a task as removing a lighthousereflects the highest credit upon the engineer, John Murray.
From this port upwards of 1,300,000 tons of coal are annually shipped, and it isreckoned in importance the fourth port of the United Kingdom .
South Shields and North Shields occupy the banks at the mouth of the Tyne . Tyne-mouth, which is about 1J miles distant from the former, has a lighthouse 61 feet high,which rises 168 feet above the level of the sea.
Fig. 332.
BERWICK UPON TWEED,