As at the Centennial Exhibition in 1876, a prime mover is the central figure in the building. There it was the immense Corliss steam engine. Here it is a Diesel, started by President Wilson by wireless on the opening day, and generating all the direct current used in the palace. Another commanding exhibit is a 20,000 horsepower hydro-electric generator, significant of the modern use of water-power. The United States Government is the largest exhibitor in the building, with numerous fine models of warships, docks, dams and submarine mines; torpedoes, artillery, armorplate and shells, army equipment, ammunition-making machinery in operation, light-houses and aids to navigation, and a splendid set of models illustrating road-making methods. Crowded out of its proper place in the Palace of Liberal Arts, the exhibit of the printing trades occupies a section here, including a huge color press turning out illustrated Sunday supplements. The Palace of Mines and Metallurgy offers ample evidence of the great figure which steel now makes in the world, and of the vast extent of the petroleum industry. Here, too, as in Machinery Hall, accident prevention is emphasized. From this point of view insurance exhibits are not out of place here. The United States Steel Corporation, with its subsidiary companies, shows in this palace the largest single exhibit seen in the Exposition, save those of the United States Government. Noteworthy are its excellent models of iron and coal-mining plants, coke ovens. furnaces, rolling mills, docks, ships, and barges, and an extensive section devoted to the welfare of employees, with model playgrounds. Many states and nations, and many world-famous mining companies are represented by exhibits of ores and metals, of mine models, and mining and metallurgical processes in operation. California shows a gold dredger and a hydraulic mine in operation. The great copper mines of California, Montana, Utah, and Japan, have installed significant exhibits. The United States Government operates in this palace a model mint, a model post office, and features a daily "mine explosion," with a demonstration of rescue work. The Palace of Transportation places its emphasis on automobiles and roads, electric locomotives and cars, and the mammoth types of modern steam locomotives. All of these exhibits represent construction of the last year, with one exception. The first Central Pacific locomotive stands beside a Mallet Articulated engine,--an enormous contrast. One third of the floor space is filled with steam and electric locomotives and modern cars. Some are sectioned, and operated by electric motors, vividly illustrating the latest mechanical devices. Another third of the palace is devoted to motor cars. The Ford Motor Car Company maintains a factory exhibit in which a continuous stream of Fords is assembled and driven away, one every ten minutes.