Page:Popular Science Monthly Volume 62.djvu/54

48 for purposes of study and comparison. Numerous methods of preparing such records have been elaborated at length by Mr. Francis Galton whose eminent labors upon the comparison and classification of the apical patterns have resulted in an elaborate and accurate system of personal identification, and for these the reader is referred to Chapter III. of his 'Finger Prints.' The method found by the present author to be the most practicable is a slight modification of Galton 's printingink method and may be best explained by a quotation from a set of direction prepared for the use of those willing to assist him in the collection of prints.

The method of printing is a simple one, the only needful apparatus being (a) a tube of best quality black mimeograph ink, (b) a rubber roller six inches long, such as is sold with photographic outfits, and (c) white, unruled paper of a suitable size and quality. A large slate for spreading the ink is a useful accessory, but a smooth sheet of paper pasted upon a flat board or piece of cardboard will fulfil the requirements in this particular.

In printing, a bit of ink should first be squeezed from the tube upon the slate or other surface used and should be spread evenly by rolling the rubber roller back and forth in various directions, until a thin layer of uniform thickness is spread over the flat surface. When the surface is in exactly the right state the palm or sole to be printed should first be wiped dry and applied to it, pressing it down from above and taking care not to move it from its original position. The pressure should be applied especially to all regions which, like the center of the palm, are naturally raised above the level of the other parts, and the fingers should be spread a little apart and pressure applied between them. In removing the member from the inked surface hold the corners of the latter and lift it quickly, beginning at the wrist or heel. By now placing the member in the same position upon a clean piece of paper and by repeating the pressure and other manipulations a print will be obtained. Finally, a little turpentine may be used to clean the roller and the surface of the skin.

Prints formed by the above methods reproduce the exact course of every papillary ridge and may be studied at ease, drawn upon and compared with one another in ways never possible in the case of the actual surfaces; besides which, the contrast of the black ridges with the white interstices (white if the ink has not been used too plentifully) causes the markings to show with far greater distinctness than when presented in the uniform tints of the natural flesh.

In order, however, that such a print should furnish much instruction, it should be interpreted, that is, mapped out morphologically into its natural areas, a proceeding which is always the first step in the study and which causes the prints to appear somewhat as in the examples given in Fig. 6. In the case of the hand, such an interpretation should begin by the determination of five fixed points, or tri-radii, four of which, the palmar tri-radii, are below the bases of the four fingers and