=210. Peace Time Uses of the Airplane.= During times of peace airplanes are useful in exploring and for carrying passengers and light freight. Airplanes scarcely more expensive than the earlier automobiles can now be bought. [Sidenote: =Airplanes carry the mail=] Airplanes in this country are chiefly used for carrying mail. "The mail must fly" is the slogan of the mailmen of the air, and in storm or fog--even in the face of a tornado--it has gone. In May, 1919, a hydroplane belonging to the United States navy made the first trip across the ocean. A hydroplane is an airplane having a boat-like body so that it is able to alight on or rise from the water. [Sidenote: =Transatlantic flights=] In July a British dirigible flew across with its crew. A few weeks earlier a British plane flew from continent to continent in less than sixteen hours. It took Columbus seventy days to make his crossing. JOHN P. HOLLAND, WHO TAUGHT MEN HOW TO SAIL UNDER THE SEA [Sidenote: =Bushnell and Fulton and the undersea boat=] =211. The Submarine.= During the War of the Revolution an American named Bushnell worked on the problem of making a boat that would sail under the surface of the sea. He was the first to work on this problem and is called the Father of the Submarine. Some years later Robert Fulton (page 257) became interested in the submarine. In 1801 he built one for the French government. But Fulton turned his efforts to making steamboats and did not continue his plans for a successful diving boat. [Sidenote: =John P. Holland, 1842=] =212. John P. Holland.= John P. Holland was born in Ireland in 1842. He was a studious boy and became a teacher. The stories of Bushnell and of Fulton interested him and he studied carefully what they had done. He came to America and settled in New Jersey. There he got a position as teacher in a parochial school. He continued his study of the undersea boat making many experiments and tests. Holland's first submarine became stuck in the mud. But he did not give up. His next boat he called the "Fenian Ram." It frightened people when it suddenly raised its head out of the water and as quickly disappeared. [Illustration: JOHN P. HOLLAND _From a photograph_] In 1895, after a number of severe tests, Holland succeeded in interesting the United States Government in his plans. He built for it a submarine which he named the "Plunger." [Illustration: A SUBMARINE] Holland now formed a company to build his boats. In 1898 he produced the famous Holland submarine. This boat settled any doubt about what submarines could do. It was only fifty feet long, but it could dive under water and rise again at the will of the inventor. From that time the Holland company built many submarines for all the great nations of the world. [Sidenote: =The periscope=]