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or THE 



UNIVERSITY 



CHAP. IX. NHEERXESS DOCKS. 249 



the current in the Medway, from which the ships entered 

 the port. 



The coffer-dams in which these Cyclopean walls were 

 built demand a passing notice because of their gigantic 

 dimensions and the great depth at which they were 

 placed, not less than from 27 to 28 feet below low water 

 of spring tides. They were composed of four rows of 

 piles about 12 to 14 inches square. The two centre 

 rows were carried about four feet above the level of 

 high water of the highest spring tides, and were driven 

 from 20 to 30 feet into the sea-bottom. The outer and 

 inner rows were about seven feet from the two centre 

 main rows, but only extended up to the level of the half 

 tide, and were driven from 15 to 20 feet into the ground. 

 All the piles were hooped and shod with wrought 

 iron, firmly bound together at the bottom, middle, and 

 top, with timber braces and wrought iron bolts and ties 

 in every direction. The joints were caulked with oakum 

 covered with pitch, and the spaces between the piles 

 were filled with well-tempered clay, so that they were 

 as nearly water-tight as possible, notwithstanding the 

 tremendous weight of the sea outside at the top of 

 every tide. Though the dams somewhat changed form 

 by this pressure and inclined inwards, the piles were 

 prevented being forced in that direction by powerful 

 counteracting braces, and the whole stood fast until the 

 completion of the work, contrary to the expectations of 

 many, who regarded it as an altogether impracticable 

 thing to construct coffer-dams of such magnitude in so 

 exposed a situation, where the pressure to be resisted 

 was so enormous. The only accident which occurred 

 to the coffer-dams was in 1820, when the old Bellerophon 

 line of battle ship, which had been anchored outside to 

 break the swell, was forced from her moorings by a 

 fierce storm from the north-east, and driven against the 

 piling, a large extent of which gave way, and the 

 waters rushed in upon the works. Fortunately, the 



