Heretofore the best judges of money have had nothing as a guide in judging at sight but experience in handling money, a familiarity with the notes of a few particular banks, and the general appearance of a note. They become familiar with a certain (to them) undefined perfect appearance, generally possessed by genuine notes, and any apparent want of which creates suspicion as to the genuineness of a note; but the first impression, they affirm, is the best, as sometimes upon continued examination the judgment, having no particular guide, wavers, gets confused, and is often at fault. Now this uncertainty may be entirely obviated, and the detection of counterfeits at sight reduced to a perfect science or mathematical certainty; and this great desideratum is held to be perfectly attained in the rules here presented, when combined with a little practice in handling money. All genuine Bank Notes in the United States are engraved upon one uniform principle, by regular Bank-note Engraving Companies. A company consists of ten to twenty first-class artists, each perfect in his own department; there is required a heavy capital to be invested, and the use of perfect, costly and inimitable machinery. Since the invention of the Geometric Lathe, Ruling Engine, and Medallion Ruling, and the invention of transferring engravings by Perkins, it has been rendered entirely out of the question--in fact, a physical impossibility--for any genuine note to be perfectly imitated. Counterfeiters cannot procure all the machinery; and even supposing they could, it would be against their own interest to invest $50,000 to $100,000 in an illegitimate business, to run the hazardous risk of seizure and confiscation. It would be more to their interest to invest that amount in any honest business. They therefore attempt to imitate the several kinds of inimitable engine-work by hand, and the imitations thus produced vary in character from miserably poor to tolerable, and sometimes exceedingly close imitations--deceiving the best judges who do not understand the principle, but detected at a glance by any one understanding it, as it is explained and illustrated in the following pages. Sometimes they get hold of one or more worn-out stolen genuine dies and use them in their issues--and so far their work will be genuine; but there is always enough else of the other portions of the work to indicate a counterfeit note. The following items, quoted from newspapers (June, 1850), will serve to show the necessity of the diffusion of some system of infallible detection at sight:-- 🖙 “The Western States, it is said, are flooded with $2 bills of the State Bank, Indiana.”--_Times._