(Continued from page 231 ) The gigantic presses we have last described are only employed by a few of the leading journals, whose circulation is very large, mdash;the majority of printers still using the ordinary power-presses, except for fine book-work, when Adam's press is generally employed here, but previously to giving a description of this latter kind we will take a cursory glance at the other varieties of pylin-drical presses. In the typn-cylinder machine it is evident that the columns of type, strictly speaking, iorm the sides of a polygon, but the breadth of the columns is so small, compared with the diameter of the cylinder, that their surfaces depart very little from the regular cylindrical form, the diameter of the type drum being 4 feet, and sometimes over 5 feet, but if this principle were applied to small presses, the type-drum being made of proportionate diameter, and having only one cylinder or perhaps two, for the paper, it will be apparent that the polygonal sides formed by the type would be a serious detriment to the operation. In his last patent, Applegath proposes to remedy this defect by using two type cylinders, so arranged that each will carry only one halt of the number of columns required. The columns being placed on either type cylinder, alternately, so that the paper first comes in CDntact with one type-cylinder, and having been impressed by the columns fixed upon it, then encounters the type upon the other cylinder. Such an arrangement would allow the type drums to be very much reduced in size, and by making the type of a taper form a still further reduction might be made. Taking as an instance a case in which the circumference of the cylinders was 200 inches, his modification would allow the circumference to be reduced to 70 inches, and with taper type the cylinder need not be more in circumference than the size of the sheet of paper when measured across the columns. The proposition of using taper type is somewhat analogous to a plan proposed as far back as 1792. A new method for printing both sides of the sheet, when the paper is once fed to the press, is also indicated in the same patent, but this latter operation, which,by-the-way, is not entirely original, is not of so much importance as many are inclined to suppose, for an equivalent advantage can be gained by an arrange, ment well known to printers. For this purpose it is only necessary to make the press -sufficiently wide to print a sheet large enough to make two copies, when, if the form forboth sides be placed on the type cylinder, and a sheet of paper supplied, it will issue from the press having the two halvesof the paper printed on it. Now let it be passed through the press again, so that the other side may be similarly printed, and it will be seen that two copies are obtained by a process as quick as that just mentioned, and which is much more simple. The use of revolving type cylinders has been adopted by some printers who carry on business in this city, for book-work, the press employed being in some respects similar to that used for newspapers. It is adapted to print on both sides during the passage of the paper from the hands of the pressman to its egress by the fly-frame, and the following is the manner ot operating:mdash;Two type-drums are employed, each having a paper or tympan cylinder, directly over it, so thaS'after the sheet has received an impression on one side, it is released and allowed to fold around the other cylinder in such a manner that the unimpressed side is presented to the type. This press appears well adapted for printing periodicals or cheap books, and is employed for stereotype printing. The above-mentioned machines are all, however, of very recent date, and by the far greater proportion of printers the Napier press is still employed. It differs greatly from those already described, in having a flat type-bed which moves forth and back horizontally, the paper being folded around a revolving cylinder, which, in its circuit, presses the paper against the form. Such was the leading principle of nearly all the power-presses until within the last few years. Their chief defect lies in the necessity* of reversing twice the direction in which the bed is moved for each impression, the magnitude of this evi will be understood by instancing a press of the largest size in which the weight of the bed and type amounted to a ton, which mass had to travel a distance of 88 inches in each direction, it was found that so great a weight could not be driven along such a space with safety at a greater rate than about 45 strokes per minute, which limited its maximum producing power to 5,000 sheets per hour. The momentum of this heavy mass is counteracted by powerful springs, which, at the termination of the stroke either way, receive the shock imparted by the moving bed, and by means of their recoil, dimish the resistance to the retrograde motion. When a bed is to be moved at so high a velocity, it will be easily conceived that the friction would be enormous were it to move on a plane surface, but by causing it to rest on rollers the friction is greatly diminished. There are many variations in minor points among the different species of this description of press, but in the leading principles they are all similar, although some are adapted for rapid, and others for neat typography. There is, however, one ingenious contrivance, common to them all, namely, that by which the paper is pulled forward at the proper time, then grasped by the fingers of the cylinder until the impression having been imparted, they relax their hold, and the paper is carried by the tapes to the fly frame. There are other kinds of power-presses \ery different in construction to those just mentioned, and which bear a greater resemblance to the hand-press, the most prominent of these is the press manufactured by Adams, of Boston, and which has acquired a high reputation amongst that class of printers who aim rather at excellence than rapidity. It differs from its prototype, the hand-press, in employing a bed which moves up to give ?n impression, whilst the platen remains stationary, which plan is the reverse of that adopted for the Viand-press. The paper having been supplied by the pressman, it is, by means of fingers or clips, carried under the platen; here it pauses, leceives the impression, and is carried by tapes |or some distance horizontally, when it rises, in order to reach the fly-frame, which operates in the usual manner ; the inking process is effected by giving the bed a horizontal motion in addition to its vertical movement. The performance of the larger machines of this de-icription we believe will amount to 600 copies per hour, which appears a small number when compared with the 20,000 copies of the revolving type press, but our readers must recollect that whilst the one is intended for rapidity, the other is intended for excellence. (To be Continued.)
This article was originally published with the title "Machinery and Tools as they are.—Printing Presses"