Page:On the economy of machinery and manufactures - Babbage - 1846.djvu/98

64 ink: but the most perfect economy was only to be produced by mechanism. When printing-presses, moved by the power of steam, were introduced, the action of these rollers was found to be well adapted to their performance; and a reservoir of ink was formed, from which a roller regularly abstracted a small quantity at each impression. From three to five other rollers spread this portion uniformly over a slab, (by most ingenious contrivances varied in almost each kind of press,) and another travelling roller, having fed itself on the slab, passed and re-passed over the type just before it gave the impression to the paper.

In order to shew that this plan of inking puts the proper quantity of ink upon the type, we must prove, first,that the quantity is not too little: this would soon have been discovered from the complaints of the public and the booksellers; and, secondly,that it is not too great. This latter point was satisfactorily established by an experimentexperiment. [sic] A few hours after one side of a sheet of paper has been printed upon, the ink is sufficiently dry to allow it to receive the impression upon the other; and, as considerable pressure is made use of, the tympan on which the side first printed is laid, is guarded from soiling it by a sheet of paper called the set-off sheet. This paper receives, in succession, every sheet of the work to be printed, acquiring from them more or less of the ink, according to their dryness, or the quantity upon them. It was necessary in the former process, after about one hundred impressions, to change this set-off sheet, which then became too much soiled for further use. In the new method of printing by machinery,