Forged articles have another advantage which we should not overlook. The physical properties which are imparted during forging are somewhat superior to those which the rolls bestow. The physical properties shown by the latter are very satisfactory, however. CHAPTER XVII THE ROLLING PROCESS [Illustration: EARLY ROLLS ] After invention of the puddling furnace with its rather large yield from the standpoint of those days, Cort about 1783 found the hammering method unsatisfactory for his purposes and rolls were devised by him to facilitate working of the larger balls of iron which his furnace produced. His rolls were provided with a series of grooves which systematically reduced the balls of iron to pieces of longer and longer length and proportionally decreasing diameters. They were power driven and served very well as long as iron and steel were made in quantities no larger than those which were produced in the puddling and crucible furnaces. Quite naturally there was little or no change in the essentials of rolling mill design until it was forced by the invention of the Bessemer steel-making process. With that occurrence trouble began. The open-hearth process followed, and, with the increasingly large steel outputs of mills using these processes, necessity after necessity developed which resulted in the highly developed rolling mills of to-day. [Illustration: [Mill]] The “Two-High” Mill The mill as invented by Cort had but two rolls and these were actuated by a fly wheel. Turning in one direction continually, the rolls allowed the piece being rolled to go through in only one direction, i.e., it had to be returned from the rear to the front side of the mill after every passage, usually called “pass.” This was done by the “catcher,” a brawny man at the rear of the mill, seizing the piece, lifting one end bodily to the top of the upper roll over which it was carried back with more or less difficulty and awkwardness to the “roller,” who, from the front, seized and entered it again into the next succeeding or smaller groove of the rolls. [Illustration: TWO-HIGH ROLLS AND EFFECT ON THE PIECE ] The “Three-High” Mill [Illustration: ACTION OF THREE-HIGH ROLLS ] In 1857 John Fritz was watching his men at their slow and fatiguing work at the two-high mill of the Cambria (Pa.) Iron Works. The thought struck him that by adding another or third roll at the top, the piece could also be given a pass on every trip back to the roller in front. The rolls would of course pull it through, the work would be less severe on the men, and, receiving passes in both directions, the piece would receive the full number in approximately one-half of the time which was then required, and, more important than all else, it would not have nearly so long a time to cool and could be finished at a more desirable temperature—a great advantage.