98 ANNUAL OF SCIENTIFIC DISCOVERY. 



well as those of the basin, should be bevelled in such a manner as to lock the 

 whole way round in a collar with a corresponding gi-oove; this collar opens 

 and closes upon the edges the whole way round, by means of two hinges 

 and wide-threaded, strong screws, or else by means of a cam, or eccentric 

 lever-lock. A very simple contrivance compels regularity in the proceeding, 

 and prevents accidents, by locking the stop-cock, and preventing the admis- 

 sion of pressure into the basin, until after the plate shall have been shut 

 down and firmly locked upon the tympan. 



The engraved plate may either be permanently fastened upon the iron 

 plate, or it may be run into its place in a groove, so as to admit of being 

 easily removed and replaced after each impression, as in the case of copper- 

 plate printing. 



When it is intended to print paper-hangings or cloth with dies, an iron 

 frame, instead of the solid plate above described, is attached to the hinges; 

 a strong iron axle, passing through, gudgeons on opposite sides of the frame, 

 carries a panel fitting into the frame, and upon this panel the die is fixed. 

 The panel thus revolving completely on the axle at the same time that the 

 frame is raised upon its hinges to a vertical position, admits of the face of 

 the die being alternately brought in contact with the tub, when it is charged 

 with color, and with the surface of the material intended to be printed. 



2. Another form of the press is one in which the tympan is movable upon 

 hinges, and fastens down upon the plate, which in this case is the fixed part 

 of the press, and iipon it the die is laid. In lithography or typography, 

 there must, of course, be a hollow in the plate corresponding to the thickness 

 of the stone or type used. 



This was the form adopted for the first experiment of the press, its tym- 

 pan consisted of two sheets of vulcanized caoutchouc fastened to the basin, 

 and secured by strong screws ; the tympanum and the plate, instead of being 

 locked together while the pressure was on, by means of the collar above de- 

 scribed, were kept together at one end by the hinges, and at the other by a 

 cam, or eccentric lever-lock, working from an iron arch like a common letter- 

 cop3'ing machine, and to which two movable claws are attached, which, 

 when the lever is worked, grasp and secure the ends of a strong bar across 

 the centre. 



3. It may sometimes be desirable to place the press vertically, notwith- 

 standing the slight, and in fact almost imperceptible difference in the pres- 

 sure at the top and at the bottom of the basin, and which is produced by 

 the column of water in the basin itself. When air is used, this inequality is 

 absolutely imperceptible; but, on account of the great compressibility of air, 

 a much larger quantity of air must be admitted than when water is used. 

 For instance, if the basin is one metre square and one millimetre deep, and 

 consequently holds one litre, it will require one litre of air to produce a pres- 

 sure of a single atmosphere, and ten litres to produce a pressure of ten 

 atmospheres. 



The vertical position is particularly well suited for very large plates, say 

 five or six feet square ; the copperplate can, if necessary, be heated from be- 

 hind, and the workmen can apply the ink in a standing posture. The press, 

 in this case, would open like a door, and large presses thus arranged would 

 occupy but little space, would be easily worked, would render the application 

 of the ink less fatiguing, and would save rent in office space; for six vertical 

 presses take no more room than two horizontal presses. In this way the 

 printing of very large maps will become not only possible, but cheap. 



