With the Tesla turbine this disadvantage, as we have seen, is entirely done away with, and the one turbine can be reversed as easily and simply as it can be started. And so, while we are waiting for the world-moving wireless transmission of power and for the completion of Tesla's invention for safe and stable airships, we can look for the speedy development of his turbine in practically all departments of mechanical engineering. CHAPTER IX THE ROMANCE OF CONCRETE THE ONE-PIECE HOUSE OF THOMAS A. EDISON, AND OTHER USES OF THE NEWEST AND YET THE OLDEST BUILDING MATERIAL OF CIVILIZED PEOPLES SEEN BY THE BOY AND HIS SCIENTIFIC FRIEND While we are looking around at all these epoch-making inventions let us follow our friendly scientist and his boy companion to one of the big cement shows held in the various large cities of the United States every year, for a glance at some of the uses of reinforced concrete in modern engineering and building. For the boy who intends to become a civil engineer this wonderful material will have an especial interest, because its successful use in all of the greatest engineering works going on to-day has brought it to the front as the modern substitute, in a great many cases, for wood, brick, or expensive stone and steel structures. [Illustration: WHAT ONE SET OF BOYS DID WITH CONCRETE This Indian tepee of concrete was made by the boys of Dr. W. A. Keyes' summer school, at Sebasco, Maine. The picture on the left shows the method of construction.] [Illustration: MASSIVE CONCRETE WORK Completed side walls of solid concrete in the Gatun Locks of the Panama Canal.] [Illustration: A LEVEL STRETCH OF CATSKILL AQUEDUCT Showing completed section as well as forms for the concrete.] On entering the cement show our friends saw on every side long rows of booths showing models of structures and articles that could be made of concrete. There were models of houses, subways, dams, bridges, dock works, retaining walls, sewers, bridges, pavements and even boats and furniture. In fact, so the men in the exhibition booths said, concrete can be used for practically every building purpose where strength, lasting qualities, and resistance to heat and cold are needed. "This is the concrete age," they declared. "Concrete is fireproof, waterproof, sanitary, and resists frost when properly used. Our timber supply is decreasing, the supply of iron ore for structural steel is limited, and stone is expensive; so concrete, reinforced with steel, and used by engineers who understand their business, will be the greatest building material of the future." These are the things that the enthusiasts at all the concrete shows say, but they admit that there are certain kinds of construction in which concrete is not as effective as steel or granite. Also they say that the use of reinforced concrete requires the highest type of engineering skill, and a complete understanding of the technicalities of the subject.