Page:Popular Science Monthly Volume 90.djvu/113

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Is that Ten-Dollar Bill Good or Bad?

��Captain Porter of the United States Secret Service invents a machine which detects counterfeit money

���A good bill is placed on one of the oblong metal plates nnd the suspected counterfeit on the other so that the various orna- ments on the two may be compared according to squares

��A NEWEST aid to the prevention of counterfeiting is a contrivance re- cently invented by Capt. Thomas I. Porter, head of the Chicago office of the United States Secret Service. His machine is especially intended to detect counterfeit bills or coins at the moment the possessor attempts to pass them at a bank. Through the aid of modern processes of printing and engraving counterfeits can be made so much like originals that they defy ordinary inspection. A special machine is necessary.

Captain Porter's contrivance depends on the principle that a counterfeiter rarely suc- ceeds in making perfect original plates for his bills. Somehow or other there is always I slight distortion in some part. To the casual eye the products of the counterfeiter look exactly like those of Uncle Sam. But most plate-engraving processes make use of photography at one stage or another. The images of the bills must pass through a lens, which passage is sure to distort them. Though the distortion is slight, minute comparison with a good bill reveals the de- fects. The new machine is designed to make the work of comparison easy.

��The detector consists simply of a thick wooden frame about ten inches or a foot square. On the top surface, brass edgings are provided which hold in place a large plate of glass — this being divided into squares about one-fourth of an inch apart. Several glass plates are provided, each with a different set of rulings suited to the fine- ness of the bill undergoing test. Beneath the glass plate are two thin oblong metal plates faced on their upper surfaces with blotting paper or other material having a rough surface to which a bill will readily adhere. These metal plates rest side by side beneath the glass and are provided with handles at each end extending be- yond the glass. By means of the handles the bills may be shifted around under the glass at will.

In using the machine, a good bill is placed on one of the oblong metal plates, and the supposed counterfeit on the other — each adhering to the blotting-paper upF>er surface of its respective plate. The ruled glass is then placed down over the metal plates and their accompanying bills, and

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