[Illustration: FIG. 237.--DETAILS OF INTERNAL CONSTRUCTION.] The construction of iron buildings began about the middle of the century. In 1845 Peter Cooper erected the largest rolling mill at that time in the United States for making railroad iron, and at this mill wrought iron beams for fireproof buildings were first rolled. In the building of the Cooper Institute in New York City in 1857 he was the first to employ such beams with brick arches to support the floors. The unifying of the iron work into an integral skeleton frame, for relieving the side walls of the weight of the floors is, however, a comparatively recent development, and this has so raised the height of the modern office building as to cause it to impress the observer as an obelisk rather than a place of habitation. An earthquake-proof steel palace for the Crown Prince of Japan is one of the modern applications of steel in architecture. It is being built by American engineers, and is to cost $3,000,000. [Illustration: FIG. 238.--THE EIFFEL TOWER. HEIGHT, 984 FEET. TALLEST STRUCTURE IN THE WORLD.] [Illustration: FIG. 239.--WASHINGTON’S MONUMENT. HEIGHT 555 FEET, 5½ INCHES. HIGHEST MASONRY STRUCTURE IN THE WORLD.] _Eiffel Tower._--Loftiest among the high structures of the world, and significant as indicating the possibilities of iron construction, the Eiffel Tower of the Paris Exposition of 1889 was a distinct achievement in the engineering world. It is seen in Fig. 238. It is 984 feet high, and 410 feet across its foundation, and has a supporting base of four independent lattice work piers. In the top was constructed a scientific laboratory surmounted by a lantern containing a powerful electric light. The total weight of iron in the structure is about 7,000 tons, the weight of the rivets alone being 450 tons, and the total number of them 2,500,000. The level of the first story is marked by a bold frieze, on the panels of which, around all four faces, were inscribed in gigantic letters of gold the names of the famous Frenchmen of the century. The summit of the tower was reached by staircases containing 1,793 steps, and by hydraulic elevators running in four stages. The cost of this structure was nearly $1,000,000.