29. On this galley, the lines are accumulated in long columns, which are afterwards divided into pages, and tied together with a string, to prevent the types from falling asunder, or into _pi_, as the printers term it. A sufficient number of pages having been completed to constitute a _form_, or, in other words, to fill one side of a sheet of printing-paper, they are arranged on an _imposing-stone_, and strongly locked up, or wedged together, in an iron _chase_. 30. The first impression taken from the types is called the _proof_. This is carefully read over by the author or proof-reader, or both, and the errors and corrections plainly marked in the margin. These corrections having been made by the compositor, the form is again locked up, and delivered to the pressman. 31. The pressman having dampened his paper with water, and put every part of his press in order, takes impressions in the following manner: he places the sheet upon the _tympan_, and confines it there by turning down upon it the _frisket_; he then brings them both, together with the paper, upon the form, which has been previously inked. He next turns a crank with his left hand, and thereby places the form directly under the _platen_, which is immediately brought, in a perpendicular direction, upon the types, by means of a lever pulled with his right hand. 32. After the impression has been thus communicated, the form is returned to its former position, and the printed sheet is removed. The operation just described, is repeated for each side of every sheet of the edition. In the cut at the head of this article, the pressman is represented as in the act of turning down the frisket upon the tympan. The business of the boy behind the press is to apply the ink to the types by means of the _rollers_ before him. In offices where much printing is executed, the roller-boy is now dispensed with, simple machinery, attached to the crank of the press, called a _patent roller-boy_, being substituted in his place. 33. Within the present century, great improvements have been made in the printing business generally, especially in the presses, and in the means of applying the ink. In the old _Ramage_ press, the power was derived from a screw which was moved by a lever; but, in those by several late inventors, from an accumulation of levers. 34. In 1814, printing by machinery was commenced in London, and rollers became necessary for inking the forms. These were made of molasses, glue, and tar, in proportions to suit the temperature of the weather. From these originated composition balls in the following year, and in 1819, hand rollers. Formerly the ink was applied by means of pelt balls stuffed with wool.