Page:Popular Science Monthly Volume 63.djvu/401

Rh board or table placing upon it a little of the ink, and then rolling it down with the roller until the paper is coated with a uniform thin layer of ink. The best results are obtained when this is thin enough to appear of a dull green color rather than black, and the usual difficulty lies rather in using too much than too little ink. The hand or foot to be printed is then laid upon the inked surface, pressed a little, especially at the places which are naturally raised above the paper, and then removed and laid in the same way upon a clean sheet of paper, pressing the parts as in the first instance. Care must be taken not to slip the hand or foot sideways at any time, as this would blur the lines; a similar condition may be caused by too great pressure, and thus when the feet are taken the subject should be seated, allowing the foot to be manipulated by a second operator. The inking surface should be freshly rolled before each new impression, and when a number are taken at one time, a little ink must be occasionally added and rolled down. If mimeograph ink is not available, ordinary printer's ink will do almost as well, and both sorts may be readily removed from the skin by the use of a little turpentine or benzine, or even by soap and warm water.

After a collection of imprints has been made, the next procedure is the interpretation, that is, the tracing out of certain definite lines which mark the course of the ridges and define the patterns. As the palm presents simpler conditions than does the sole and is much the best for purposes of instruction, we will begin with a good average print like that given in Fig. 1, using a sharp-pointed pencil, and, when necessary, a reading glass of low power. At the base of each of the four fingers there will be seen a triangular area composed of transverse ridges, so intruded into the palm that it parts for some little distance the ridges which belong more definitely to the palm itself. These are the four digital areas, and at their apices are found points from which the ridges radiate in three directions, two bounding digital areas and one traversing more or less of the palm. These four points or triradii (equivalent to Galton's 'deltas') are the starting points of the system and may be termed the four digital triradii, numbered 1-4, beginning at the inner or thumb side. The lines bounding the digital areas are the eight digital lines, numbered from 1-8, and the four other lines which proceed from the triradii and cross the palm are the four main lines. These latter, designated by the letters A-D, are of primary importance and furnish by their course the first or primary formulæ by which the palms are classified. These lines are established by following the direction of the ridges to whatever point they may lead, and are best traced along a certain definite ridge, although, in places where a ridge that is being followed breaks or forks, the line should be continued by means of an adjacent ridge, or by taking the general