BANK NOTE MACHINERY. Consider ble mechanical ingenuity has been shewn in devising the best mode of manufacturing bank notes, so that they shall be light, durable, and not easily imitated by forgers. The making of the paper, the engraving of the steel-plate, and the numbering of the notes, have all called forth this ingenuity.
It was stated some short time ago in the public journals that many of the banks in the United States have adopted the use of a pace liar kind of paper made expressly for bank notes. There are introduced into the body of the piece of paper for each note as many cotton threads as will shew the value of the note in dollars, Up to certain limits; or at least, that a definite number of threads shall represent a definite value in the note ; so that no chemi cal or mechanical tampering with the printed part of the note will prevent the paper from revealing the true original value.
In respect to the plates from which bank notes are printed, they used to be formed of copper ; but as this material soon wears away, a mode of using steel plates was devised by Messrs. Perkins and Heath, by which a sur prising number of copies may be taken. A block or thick plate of steel is softened on the upper side ; the device is engraved on this softened surface ; the block is hardened by a very careful process after the engraving ; the device is transferred from the hardened block to the convex sin-face of a small soft steel roller, by intense pressure ; the roller is hardened, and the device is transferred from it to any num ber of softened steel plates; these plates are hardened after the transfer, and are then in a state to be printed from. By this beautiful train of operations one originally engraved block is made to suffice for an almost endless number of printings.
The mode in which the writing, the em blems, and the ornaments are combined in a bank-note, is so planned as to render forgery difficult. The numbering is a remarkable pro cess, as now performed. In 1809, the bank adopted a numbering press invented by Mr. Bramab, by which the expense and un certainty of finishing annually a large number of bank notes with a pen was materially di minished, and forgery rendered more difficult. The machine was, however, so far incomplete that it produced only units, the tens and hun dreds requiring to be brought forward by hand. In 1813 a machine invented by Mr. John Oldhatn, and used at the Bank of Ireland, had the additional power of effecting numerical progression, from 1 to 100,000 by its own operation ; one of these machines was subsequently attached to each press for printing the body of the notes, in order to register and check the number of notes pass ing through the press.
In 1819 Mr. Bryan Donkin invented a counting machine, applicable to the number ing of notes. Like most others of the kind, its action depended on the relative motion of a series of ratchet wheels with projecting rims, having notches cut in them ; so that When the first wheel counted units, the second wheel indicated tens, and so on progressively. When Mr. Thomas Oldham succeeded his father, Mr. John Oldham, as engineer to the Bank of England, he endeavoured to improve on the instruments previously constructed, and devised the form of apparatus now em ployed, which is as follows :—Four wheels each divided by ten notches, leaving a facet between each pair, engraved with consecutive numbers from 1 to 0, are placed upon a shaft ; a portion of their breadth being turned down about one-half of their depth, having a boss or collar between every two. Upon these bosses, and filling up the spaces, rest latches ; and over each wheel is a pall, the width of the first being equal to that of the unit wheel, and the breadth of the others equalling that of the wheel and latch. The palls are driven by a crank ; by each revolution of which the first wheel is moved through a space equal to one tenth of its entire circumference, bringing regularly forward the numbers from 1 to O. When the figure 0 is reached, the latch of the uecond wheel is depressed, and the wheel moves forward one division marking the tens. The same process is repeated with regard to lie other wheels, and thus any amount of lumbers can be registered, by simply in n-easing the number of wheels in proportion. Nfacliines of this lcind are extensively adopted n the Bank of England; with, of course, an nking apparatus to apply to the types.
A patent was taken out in 1844 for a mode of printing bank-notes intended to obviate the liability to forgery. The surface is covered with two designs, one geometrically regular, and the other very irregular; the two designs are engraved on different plates, and are printed with different inks, the one with visible and the other with invisible ink. Both of the inks are delible or removeable by chemical means ; and the usual engraving of a bank note is printed on paper so prepared. The rationale of the suggestion is this: that whatever means a forger might take to alter by chemical agency the letters or figures, or to transfer them by lithographic or anastatic processes, the state of the paper would betray him : for be would remove some parts of the design in the one case, and fail to transfer it in the other.