Page:The American Cyclopædia (1879) Volume III.djvu/243

 BREAKWATER 237 side were arranged eight trucks of the extreme capacity of five tons each. In discharging, these were drawn out by a windlass on deck, and upset as they passed out of the ports, each one being drawn up on the deck and run for- ward to make room for those behind. At the quarries they left the deck, and the track on which they descended over the stern being raised up, the loaded cars were run under it, into the hold. The usual cargo of 45 to 65 tons could thus be discharged in less than an hour. On Jan. 19, 1817, the work was tried by one of the most severe storms ever known. The breakwater, though in an unfinished condition, caused perfect protection to the inner harbor, where without it the damage would have been immense. Previous gales had had no effect upon it ; but this caused the upper stratum of the finished part, 200 yards in length and 30 in breadth, to be stripped, and the huge stones of two to five tons weight to be carried over from the outside, and deposited upon the northern side of the breakwater. The quantity thus re- moved was estimated at 8,000 tons. Since that time the outer slope has been "cased with regular courses of masonry, dowelled, joggled, dovetailed, and cramped together ; the diving- bell being brought into requisition for placing the lower courses, which were of granite, and were laid horizontally on their natural beds, and dovetailed, lewised, and bolted together." This work was reported by Mr. Stuart, the superintendent of the breakwater, to have been done on a slope of 5 to 1, as the sea had left it. The foot of the outer slope has also been ex- tended further out with loose stones, to give protection to the courses of masonry. The ad- ditional cost since 1841 for this and similar re- pairs has been about 200,000, making a total expense of 1,700,000. The new breakwater at Dover, in process of slow construction, is formed by an outer and inner wall of ashlar masonry, with a course of granite on the face, and blocks of concrete made with Portland cement and shingle in the core of the work to the level of high water, above which it is filled FIG. 8. Section of Dover Breakwater. with liquid concrete. The masonry commences from the chalk bottom of the bay, the blocks being placed by means of diving apparatus. Both the inner and outer walls deviate from a perpendicular about three inches to the foot, in steps. A parapet 15 ft. above the level of high water surmounts the work on the sea side. All the operations are carried on from timber staging. The water at Dover is very deep, 42 ft. at low tide, and the construction of the breakwater is upon the principle that the motion imparted by waves to water much below the surface is vertical, and that a verti- cal wall is best calculated to resist their action. There is a difference of opinion on the subject, and more time than has elapsed since such structures have been commenced will be re- quired to allow a definite conclusion to be reached. The construction of an important breakwater was commenced at Portland, on the southern coast of England, in 1849. On July 25 Prince Albert laid the foun- dation stone, and ten years later the works were so far advanced as to afford safe anchor- age to vessels. The breakwater commences with a pier which starts from the island of Portland, near the point where it is connected with the mainland. The pier runs due E. for about 1,900 ft., at which point there is an open- ing 400 ft. wide, with a minimum depth of 45 ft., to admit vessels. On the other side of this opening the outer mole of the breakwater com- mences, and, after proceeding a short distance in the same direction as the pier, turns, and extends in a N. E. direction for a distance of 6,000 ft. The pier, or inner mole, consists of a rubble mound composed of stones of all sizes, from masses of eight tons weight down to small chippings. After the mound had been well consolidated a trench was excavated in it down to the level of low spring tides and a wall of masonry erected. The face course of this wall is formed of large squared blocks, the body consisting of heavy rubble work set in water cement. The face courses, up to 6 ft. above high-water level, are of hewn granite, and the rest of the face is of the best stone from the neighboring quarries. The outer mole, or breakwater proper, is a rubble bank with a width at the base of 300 ft., at low-water level of from 90 to 100 ft., and at the top of 60 ft. The slopes on the sea face, from the bottom to a height of 12 ft., are 6 to 1 ; on the harbor face they are 1J to 1. The sheltered area is about 2,100 acres up to low water line. Con- nected with the works are two forts, an inner one on the end of the pier, and another at the further end of the outer mole. The inner fort is 100 ft. in diameter, mounts 8 guns, and stands in 9 fathoms of water. The outer fort has a rubble base 45 ft. high, and containing 140,000 tons of stone. Its diameter is 200 ft., and it stands in 10 fathoms of water. The completion of the work was celebrated with great pomp, Aug. 10, 1872, when the prince of Wales laid the top stone and declared the work finished. The execution of this magnifi- cent work is interesting as affording an ex- ample of the economical use of the force of gravity alone as a motive power in moving loads to and from a given point. The quarries from which the stone is obtained are about 380 ft. above the sea level. Three inclined planes, each having two tracks, extended down to the breakwater. A wire rope passing over a drum connected two trains of trucks, one train descending with a load while the other ascended empty. A temporary staging was