Four of our submarines in dry dock in government Navy yard

John P. Holland, a resident of Patterson, New Jersey, an Irishman by birth, built the first practical submarine. The submarines of all navies now follow the Holland idea but of course on much improved lines. The United States has 75 submarines, with more in process of construction. The "Schley," a new fleet submarine for use in the navy, is 263 ft. 9 in. long, has a surface displacement of 1250 tons, a submerged speed of 11 1/2 knots, a surface speed of 20 knots and a cruising radius of 3000 miles. It has a powerful armament of 8 torpedo tubes. A submarine has two sets of engines. Oil engines propel it on the surface and run dynamoes which generate electricity for large storage batteries. Electric engines propel the boat under water. It is submerged by letting the ocean water flow into tanks and rises to the surface by emptying the tanks by forcing in compressed air. The submarine, when submerged runs along under the surface, of the water at a depth of from a few feet to 100 or even more. If it runs too close to the surface it may be easily detected by an aeroplane. The periscope (per'i-skop), the "eye of the submarine," is a bronze tube about 4 inches in diameter and 15 or 20 feet long, fitted with reflecting prisms and magnifying lenses so that the observer in the submarine can see on the surface of the water. Very recent submarines built by Germany have 3 or 4 periscopes. The submarine maintains its equilibrium (e’kwi-lib'ri-um) by the use of a gyroscope (ji-ro-skop), by horizontal rudders and by quickly shifting the water ballast. Two of the horizontal rudders or stabilizers may be seen on the submarine in the immediate foreground. When submerged the crew breathe air from oxygen tanks. A supply sufficient for 36 hours can be carried