HYDRAULIC PRESSES AND LIFTS. 63

by wrought iron bars, two iron girders 65 feefc long, whichextend across the dock to tlie corresponding column and presson the opposite side. A wrought iron platform is thus formedwith 27 feet of water over it, when the rams are down. Therams have an area of 100 circular inches, the water-pressurebeing 2 tons per inch. This gives 200 tons lifting power foreach press, or 6400 tons for the whole. Deducting 620 tonsdead weight of working parts, the load that can be raised is5780 tons. The presses are arranged in three groups, forminga tripod on which the pontoon is carried. The presses in eachgroup are connected, and as each group is independent of theother two, the position can be either inaintained level, or at aninclination. Any pair of presses can be cut off in the valveroom, and, except in the case of the largest dass of vessels, oneor more of the end pairs is generally out of use. The water issupplied to the presses through a half-inch pipe from twelveforce pumps worked from a 50 HP engine.

In 1872 the Government of Bombay had another HydraulicLift Graving-Dock constructed by Mr. Edwin Clark, which wasan advance upon the original Yictoria Graving-Dock Lift. Thisis constructed at Hog Island, Bombay, at a point where thereis a depth of from 50 to 60 feet of water, and a inaximum riseof tide of 167 feet, and an ordinary rise of 14 feet. The lengthof the dock is 350 feet. There are two rows of cast ironcolumns, having a clear distance of 88 feet between tliem.There are eighteen columns in each row, their distances apartgradually increasing from 18 feet in the middle to 24 feet atthe ends. Each column is 7 feet 6 inches in diameter at thebase, and 6 feet 6 inches above, the length being 100 feet.They are placed in pits sunk in the soft rock, to which theyare bolted and concreted, 36 feet of the column only appearingabove high water. In each column two hydraulic presses areenclosed with solid rams, 14 inches in diameter and having astroke of 35 feet. Each press is in one piece, 35 ft. 6 in. longand it weiglis 14 tons. Two long girders, 2 ft. 7 in. deep,run along the top of each row of columns, and on fliese, girders