Because of the growth of the Republic, after half a century it became necessary to build a Senate Chamber on the north and a House of Representatives Chamber on the south. The cornerstone of the extensions to the Capitol which increased it to its present size was laid on July 4, 1851, by President Fillmore. Daniel Webster was the orator of the day. This work was prosecuted under the direction of Thomas U. Walter, Architect of the Capitol until 1865, when he resigned, and was completed under the supervision of Edward Clark. The House extension was first occupied for legislative purposes December 16, 1857, and the Senate extension January 4, 1859. The white marble used in the walls is from Massachusetts and that in the columns from Maryland. [Illustration: _Courtesy of Commercial Photo Co._ THE CAPITOL] The entire length of the building from north to south is 751 feet 4 inches and its greatest dimension from east to west is 350 feet. The area covered by the building is 3¹⁄₂ acres. The Dome of the original central building was constructed of wood, covered with copper. The present structure of cast iron was commenced in 1856, and completed in 1865. The entire weight of iron used is 8,909,200 pounds. The Dome is crowned by the bronze Statue of Freedom, 19 feet 6 inches high and weighing 14,985 pounds. It was modeled by the sculptor Thomas Crawford. The height of the Dome above the base line of the east front is 287 feet 5 inches. The height from the top of the balustrade of the building is 217 feet 11 inches. The greatest diameter at the base is 135 feet 5 inches. The Rotunda is 97 feet 6 inches in diameter, and its height from the floor to the top of the canopy is 180 feet 3 inches. The canopy overhanging the Dome, portraying the Apotheosis of Washington, was painted by Brumidi. The Rotunda frieze, 65 feet above the floor, making a circle 300 feet in length around the walls, illustrates important periods in American history. Paintings in the Rotunda are as follows: The Landing of Columbus on San Salvador, October 12, 1492, by Vanderlyn. The Discovery of the Mississippi by De Soto, 1541, by W. H. Powell. The Baptism of Pocahontas, Jamestown, Va., 1613, by John G. Chapman. The Embarkation of the Pilgrims from Delft-Haven, July 22, 1620, by Robert W. Weir. The Signing of the Declaration of Independence, Philadelphia, July 4, 1776, by John Trumbull. The Surrender of Burgoyne, Saratoga, October 17, 1777, by John Trumbull. The Surrender of Cornwallis, Yorktown, Va., October 19, 1781, by John Trumbull. The Resignation of General Washington, December 23, 1783, by John Trumbull.