than one half of a large sheet could be printed at one descent of the screw. A most serious evil results from this, especially in printing duodecimo, because the pressure necessarily is applied twice to the centre pages of each sheet, while it is applied only once to the other pages. To these disadvantages may be added, the difficulty of ascertaining and regulating the degree of pressure; the irregularity of the motion of the lever; the severe labour, and excessive exertion of the workman; the nice accuracy in placing the types under the centre;—there being no difference, in point of trouble and labour, in printing a card and a folio;—and the necessity for placing small work always in the same spot, which necessarily wears out one part sooner than the others. In obviating these defects, Mr Ruthven has completely succeeded;—and after giving some account of the construction of the new printing press, we shall point out the superior excellencies of it as briefly as possible.
The general appearance of the large press is well represented in fig. 1.; of which fig. 2. is a complete section. In this press the types are placed on a stationary coffin or tablet, P; the paper is put on in the usual manner on the tympan, a, (fig. 1.) and secured by the frisket, b. On turning over the tympans thus arranged, the platen, N (fig. 2.),—supported by the wheels, QQ,—is drawn over the coffin by the handle, U, till the lower parts of the screw bolts, M M, be fully secured in the clutches, L L (fig. 2.); the lever or handle, A, is then turned over in the front of the press till stopped, when it will be nearly in a horizontal position. It is then restored to its original situation, the platen pushed back, the tympans raised, and the printing is completed. The mode in which this movement is produced is concealed by the check, R.
The action which takes place in the above-described process will be best understood by a reference to, and examination of, the section, fig. 2. The platen is, in this, represented in its proper situation over the types. The parts of the external structure have been already sufficiently explained; it only remains to point out those which are exposed in the section. Beneath the tablet, P, and immediately behind the check, R, are the levers, I I, having their fulcra at K K; to which are attached the clutches, L L, communicating as above-mentioned with M M;
