157. Formerly, fireproof floors were almost exclusively made of concrete supported on brick arches sprung between the lower flanges of I beams, although in some cases corrugated-iron arches were substituted for the brick. The objections to these form's of construction are that the arches and the concrete are extremely heavy, the ceilings are not level, and the bottom flanges of the beams are unprotected. Consequently, a better form of construction was sought, and the brick and iron arch methods have been largely abandoned, flat arches of dense and porous tile being substituted, with much saving in weight and more complete protection of the steelwork. Considerable improvement has been made during the past 10 years in the design of tile-floor arches, and a number of systems have been introduced. In all cases, the inventor's efforts have been directed towards securing a light and economical floor, possessing sufficient strength and affording thorough fire protection.