This dry dock, which is capable of floating the largest battleship, was towed from Sparrow’s Point, Maryland, to Olangapo, Philippine Islands, a voyage of 13,000 miles. In operation, the dock is sunk by admitting water into its tanks until the ship can be floated in. The water is then pumped out and the dock with the ship inside rises to the proper level as shown.] [Illustration: U. S. BATTLESHIP “MISSISSIPPI” IN DRY DOCK AT LEAGUE ISLAND] What are Dry Docks Like? Although divers are able to go down under the water to examine the bottom of a ship while it is afloat, it is usually necessary to have it up on dry land when thorough inspections or repairs have to be made. So a berth something like a huge box stall in a stable is built, with the part where a horse would stand in the stall full of water, and a door, either made like swinging gates opening in the middle, or a caisson which is operated up and down like a window, at the end. The ship is floated into the dock and then after the door is shut to prevent any more coming in, all of the water is pumped out until the vessel rests on a lot of great big wooden blocks and supporting props with which the bottom and sides of the dock are lined. Supports are also placed between the vessel and each side of the dock. Then, when the work has been finished, and the ship is ready to go to sea, water is let back either by pumping it in or else by gradually opening the door at the end, and the vessel is able to float out into the river or harbor again. Although all of the navy yards and some private corporations in this country have docks of this kind, they are not of as much importance here as in England, where they are used, without pumping out the water, for the loading and unloading of vessels, because of the very great rise and fall of the tides there straining and otherwise damaging ships tied up to ordinary docks. There are nine important navy yards in the United States, located at Brooklyn, N. Y.; Boston, Mass.; Portsmouth, N. H.; Philadelphia, Pa.; Portsmouth, Va.; Mare Island, Cal.; New London, Conn.; Pensacola, Fla.; Washington, D. C., and Port Orchard, Wash. There is another kind of dry dock, called “floating docks,” which float on the surface of the water and may be sunk sufficiently to allow of a vessel being floated into them, and then raised again by pumping the water out of the tanks around the sides. They are usually built of iron, with water-tight compartments, and not closed in at either end. They are sunk to the required depth by the admission of water into so many of the compartments, till the vessel to be docked can float easily above the bottom of the dock, and then they are raised by pumping out the water until the ship can be propped up as in the land dry dock. Why does a Lightning Bug Light Her Light?