From the top of the submarine there extends upward a long slender tube called a periscope. When the boat is under water the end of this tube extends above the surface. By means of a certain arrangement of lenses and mirrors in this tube, the observer in the submarine can see everything on the surface of the water. In this way the boat can be guided in any direction. Holland died in 1914. [Sidenote: =Value in war=] =213. The Submarine in War and Peace.= The submarine is much used in war time. The war diver is provided with one and sometimes two tubes through which torpedoes or bombs may be fired at enemy ships while the submarine is hidden under water. It is very hard to detect a submarine when it is under the water. The only sign of its approach is a slight ripple on the surface. But if we look straight down at the water from high up in the air, then the outlines of the boat can easily be seen. In war time airplanes are used in spying out the submarine. [Sidenote: =Use of the submarine in peace=] In times of peace, too, the submarine is of great value. It is not exposed to great storms on the sea, since it can escape the waves by submerging. These boats can cross the ocean and are large enough to carry cargoes of valuable goods. In July, 1916, the world was startled by the arrival of the merchant submarine, "Deutschland," at Baltimore. Loaded with articles of trade, mainly chemicals, she left Bremen, dodged the British and French blockade, and in fifteen days reached America. One cause of America's entering the World War was Germany's attempt to starve England by a submarine blockade. [Sidenote: =Fighting the submarine=] =214. Other Inventions in the War.= The "depth bomb" was an out and out new invention. 11 could be "dropped" over the spot where a submarine was seen. Very often it blew the submarine to pieces. The "tank" was a "moving iron fort" drawn by a tractor. It could tear wire entanglements to pieces and cross enemy trenches. The "depth bomb" and "tank" were used mainly by the Allies. The wide use of "poison gas" was first introduced by the Germans. Guns able to shoot many miles were invented. One of them carried seventy miles or more. SUGGESTIONS INTENDED TO HELP THE PUPIL