Engineering Wonders of the World
Volume III

HARBOUR CONSTRUCTION. 71 blocks until they lay on the natural slope assumed by loose stones subjected to the action of heavy waves. This slope he had already decided, after careful observation, to be one of about 1 in 5. The first stone, a large block of marble, opinion ran strongly in Rennie’s favour. At the end of August 1815 nearly 650,000 tons of stone had been deposited, bringing 1,100 yards of the breakwater above low-spring tides. In this year the captive Napoleon, as he passed into Plymouth Sound, expressed INSIDE ONE OF THE DIVING-BELLS USED FOR LEVELLING THE SEA BOTTOM FOR THE CONCRETE BLOCKS, DOVER HARBOUR WORKS. went into the water on August 12, 1811. During the next two years barges brought their loads from quarries on shore, and dumped them through trap-doors in their bottoms along the line indicated by buoys. For more than a year the work had no visible effect in calming the waters of the Sound, and people who did .not understand the nature of the task began to grumble about the great expense and waste of money. In March 1813, however, the stones began to show above water, and popular his admiration at the boldness and great scale of the undertaking. Throughout 1816 stone was deposited at the rate of 1,030 tons per day—a record which could hardly be beaten at the present time, in spite of the great im- provements in methods of handling material; and by December 300 yards of the mole stood out 20 feet above low water of spring tides. Rennie had been severely criticised by his employers for using so gradual a slope as 1 in 5, and thereby greatly increasing the