When the block is finished the parts are screwed together by means of the brass bolts and nuts at the back of the block. It is then delivered to the electrotyper, who first takes a mould of the block in wax, which mould is then covered with a thin coating of blacklead, that being a good conductor of electricity. The mould is then suspended by a brass rod in a large bath filled with a solution of sulphate of copper and sulphuric acid. A strong current of electricity, obtained from a dynamo-electric machine close at hand, is conducted to the wax mould in the bath and also to a sheet of copper which is placed near the mould. The electricity decomposes the copper and deposits it in small particles on the mould, on which a thin coating of copper is gradually formed, producing an exact facsimile of the original engraved block. This copper reproduction of the woodcut is filled in at the back with metal, mounted on wood, and is then ready for the printer, who has his 'overlays' all ready, and the business of printing begins. There is nothing more wonderful in the history of printing than the rapid development of the printing machine and the extraordinary increase of its productive power. The ordinary press, though greatly improved, was found quite inadequate to the demands made upon it; and, the attention of practical men being directed to some more rapid means of production, the steam printing machine was invented. As early as 1790 Mr. W. Nicholson obtained letters patent for a machine very similar to those since in use; but it was not till 1814 that any practical use was made of the steam printing machine. In that year a German named König constructed a machine for the _Times_ newspaper, which worked successfully; but, though highly ingenious, the machine was very complicated, and it was soon superseded by the invention of Messrs. Applegarth and Cowper, possessing several novel features. This machine, again, was replaced by another where the type was arranged vertically. Then came Hoe's American machines, and finally the Walter Press, the principle of which last invention has, in the Ingram Rotary Machine, been successfully applied to the printing of cheap illustrated newspapers. By the old 'two-feeder' machines the engravings were printed on one side of the sheet, and, by a second printing, the type on the other side. They turned out 1500 impressions of the engravings in an hour, while the type side was printed (by a six-feeder American machine) at the rate of 12,000 impressions an hour. The _Penny Illustrated Paper_ is printed by the Ingram Rotary Machine at the rate of 6500 an hour. It prints both sides of the sheet at once, cuts each number to its proper size, folds it, and turns it out complete. It occupies no more space than an ordinary perfecting machine, and only requires four men to attend to it, while thirty men and five 'two-feeders' would be required to do the same amount of work by the old system.