G. Tyler Mairs states that emechanically there are two kinds of finger-prints: 'plain> and 'rolled.' The 'plain> impression is the one used exclusively by the Chinese, by Pur kenje, and later by Herschel. This is made by placing the bulb of the finger flat upon the inking surface and then upon the receiving sur face, the resulting impression being elliptical in shape, the long axis being that of the finger itself. The 'rolled' impression is made by placing the digit on the inking surface, radial side in contact, the finger-nail perpendicular to the inking surface, then rolling the bulb of the finger until the ulnar side is in contact and the nail is again perpendicular but reversed in posi tion. The bulb being thus inked, the same operations are repeated on a paper form suit able for recording the impression. This opera tion produces a cylindrical projection of the ventral surface of the digit which graphically delineates the ridge configuration in all its minutiae. Thus it will be seen that a friction skin impression (finger ,pahn or sole) is a graphical record, by personal contact, of an ex ternal physical characteristic capable of being recorded for future reference' The Chinese, like the Gypsies and many other peoples, tell fortunes by the lines upon the inside of the fingers, but the friction-skin impression ((pos sesses no occult powers of character revelation; in its gross and minute features, however, it is so permanently individual that it is an unerr ing revealer of personal identity throughout one's lifetime and as long thereafter as the culls is Epidermic ridges are still present and plainly seen in Egyptian mummies, and after a simple treatment have been definitely traced on the hands and feet of the bodies of prehistoric cliff dwellers of southern Utah.
On the researches of Herschel and Sir Francis Galton (qq.v.) Sir Edward Richard Henry, G. C. V. O., commissioner of police of the metropolis, London, England, abuilt the ex tensively used Henry System of Finger Print Classification, which enables one familiar with its intricacies to make a set of ten apical impres sions or dermatographs, classify it, and produce the person's history record (assuming one on file) in a period of time varying from five to fifteen minutes. Under this scientific system nothing is required of the subject save the set of ten apical dermatographs. Given this and nothing more, no name, no address, no physical description or photograph, the identifier 'solves for x,> to use an algebraic term. A record be ing produced, the subject's medical history, for instance, in the case of a hospital or clinic for the feeble-minded or insane, is at once avail able, no matter how long the interval between treatments, or the changed facial appearance of the subject, or similarity in names.
Many extraordinary cases are on record of criminals having been traced after accidentally leaving finger-prints at the places where the crimes were committed. In a few instances such evidence has been used in court, but cases of conviction are rare because evidence of identity is not equivalent to evidence of guilt, which must be shown by other proofs of a convincing or corroborative nature. There is a tendency to-day among criminologists to hold to the opinion that the system is most valuable when used in conjunction with other systems of identification. Consult Mairs, G. T., 'Identifi cation of Individuals by means of finger-prints, palmprints and soleprints' (in Scientific Monthly, Lancaster, Pa., October 1918).