Koenig took out a further patent on July 23rd, 1813, and a fourth (the last) on the 14th of March, 1814. The contrivance of these various arrangements cost the inventor many anxious days and nights of study and labour. But he saw before him only the end he wished to compass, and thought but little of himself and his toils. It may be mentioned that the principal feature of the invention was the printing cylinder in the centre of the machine, by which the impression was taken from the types, instead of by flat plates as in the first arrangement. The forme was fixed in a cast-iron plate which was carried to and fro on a table, being received at either end by strong spiral springs. A double machine, on the same principle,--the forme alternately passing under and giving an impression at one of two cylinders at either end of the press,--was also included in the patent of 1811. How diligently Koenig continued to elaborate the details of his invention will be obvious from the two last patents which he took out, in 1813 and 1814. In the first he introduced an important improvement in the inking arrangement, and a contrivance for holding and carrying on the sheet, keeping it close to the printing cylinder by means of endless tapes; while in the second, he added the following new expedients: a feeder, consisting of an endless web,--an improved arrangement of the endless tapes by inner as well as outer friskets,--an improvement of the register (that is, one page falling exactly on the back of another), by which greater accuracy of impression was also secured; and finally, an arrangement by which the sheet was thrown out of the machine, printed by the revolving cylinder on both sides. The partners in Koenig's Patents had established a manufactory in Whitecross Street for the production of the new machines. The workmen employed were sworn to secrecy. They entered into an agreement by which they were liable to forfeit 100L. if they communicated to others the secret of the machines, either by drawings or description, or if they told by whom or for whom they were constructed. This was to avoid the hostility of the pressmen, who, having heard of the new invention, were up in arms against it, as likely to deprive them of their employment. And yet, as stated by Johnson in his 'Typographia,' the manual labour of the men who worked at the hand press, was so severe and exhausting, "that the stoutest constitutions fell a sacrifice to it in a few years." The number of sheets that could be thrown off was also extremely limited.