Collier docks are about to be formed oppo site Woolwich, near the North Woolwich sta tion of the Eastern Counties Railway. A dock of 70 acres is planned, available not only for collier ships but for passenger steamers.
The construction of floating dry docks is now engaging the attention of engineers : the prin ciple being, to adopt a means of buoying up a ship on some kind of floating support, so as to leave it high and dry. There are now being constructed for the United States Go vernment, at Philadelphia, clocks of a re markable kind on this principle. There are ten closed compartments, called sections, capable of being exhausted of water by means of pumps ; and when so exhausted, each section can buoy up a weight of 800 tons. Six of them together would bear up a ship of the line, while four would bear a frigate. There is a stone basin or dock, 350 feet long by 226 wide. When a ship is to be dry-docked, some of the sections are filled with water sufficiently for the vessel to be floated in on the top of them ; and when brought into the basin,-the water is pumped out of the sections, and the vessel thus buoyed up. There is a railway, also, by which the vessel may be brought up completely on dry land. These remarkable works are expected
to be finished during the year 1851. Other works of a similar kind are being constructed in other parts of the United States.
The largest gates ever made for docks, per haps, are those which Messrs. Rennie have recently made for the Russian government, to be fitted up at Sevastopol on the Black Sea. On account of the peculiar locality of the town with respect to the depth of the shores, three locks were made so as to raise a ship of war to a height of 30 feet above the sea level. These locks have nine pairs of gates, varying from 21 to 34 feet in height, and from 47 to 64 feet in width. On account of the ravages of a peculiar worm, the use of wood was deter mined against, and iron substituted. The gates consist of wrought iron plates in cast iron frames ; and so enormous are some of the masses, that the engineers had to erect large and costly machinery for planing and punching them.
Our Government Dock Yards are briefly described under the names of the towns where they are situated. [CHATHAM ; PLYMOUTH, &c.)