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Comprehends a knowledge of placing the pages so that they may regularly
follow each other when printed and the sheet is folded up; and also the
mode of dressing chases and the manner of making the proper margin. As
many pages as are required for a whole or half sheet being made up, the
compositor lays them upon the imposing-stone, placing the first page with
the signature to the left hand facing him, and then proceeds according
to one of the schemes on pp. 150-199. These will be found to contain
every necessary imposition,—viz. folios, quartos, octavos, twelves,
sixteens, eighteens, twenties, twenty-fours, thirty-twos, thirty-sixes,
forties, forty-eights, sixty-fours, seventy-twos, ninety-sixes, and one
hundred and twenty-eights. We also introduce schemes for imposing from
the centre, by which means the blank or open pages may be thrown in
the centre of the form, leaving the solid pages on the outside to act
as bearers for the rollers, as well as for the better regulation of the
impression.
All odd matter, for any form, should be divided into fours, eights,
twelves, and sixteens, which is the groundwork of all the impositions
except the eighteens, which differ from all the others; for instance,
sixteens, twenty-fours, and thirty-twos are only octavos and twelves
doubled, or twice doubled, and imposed in half sheets: for example, the
sixteens are two octavos imposed on one side of the short cross; the
twenty-fours are two twelves imposed on each side of the long cross; and
a thirty-two is four octavos imposed in each quarter of the chase. Thus,
a sheet may be repeatedly doubled. By this division, any form or sheet
may be imposed, always bearing in mind that the first page of each class
must stand to the left hand, with the foot of the page toward you. Having
set down the first page, then trace the remainder according to the scheme
which applies to its number; in proof of which, the standard rule for all
other impositions may be adopted,—namely, _the folios of two pages, if
placed properly beside each other, will when added together make one more
than the number of pages in the sheet_; that is, in a sheet of sixteens,
pages 1 and 16 coming together will add up 17, and so 9 and 8 will make
17, &c.
In half sheets, all the pages belonging to the white paper, and
reiteration, are imposed in one chase. So that when a sheet of paper is
printed on both sides with the same form, that sheet is cut in two in
the short cross if quarto or octavo, and in the short and long cross of
twelves, and folded as octavo or twelves.