Personal Identification and Description 



163 



takes one axis of reference to be the "axis of the loop," i.e. a line drawn to 

 bisect the loop "at the upper end of its innermost bend," and the other axis 

 of reference the line through the single delta perpendicular to the loop axis. 

 This loop axis is very important, for it is the line upon which Galton first 

 counted the number of ridges, and much depends on two observers con- 

 structing identical loop axes before proceeding to count ridges in comparing 

 prints*. It must be remembered that the two observers may be comparing 

 two separate prints at a distance and, owing to the termination of ridges 

 and to the forking of ridges, a slight difference of position in the loop axis 

 may lead to divergent results. 



In Fig. 21 IT is "outside," 7 is "inside," the print. All in Fig. 21 (hi) 

 and (iv) is the loop axis on which Galton originally counted the ridges from 

 A to II, that at A counting zero. When the loop axis exactly passed through 

 a bifurcation Galton counted the ridges as \ r (1 + 2) = 1 \. He omits to tell us 

 what happened when it exactly passed through a ridge terminal — presumably 

 he counted it as \ — or what he did in the case of an island. 



(ii) (Hi) 



Fig. 21. Finger-print axe.s for measurements or counting of Ridges. 



Galton next proceeds to his first basis of classification. It consists in 

 paying attention solely to the deltas and the core boundaries. There may be 

 no deltas, i.e. we have a primary or arch. If there are deltas we can trace 

 the adjacent ridges from one or both deltas upward and downward. These 

 ridges will either reach the other delta, or pass above or below the corre- 

 sponding ridges from the other delta. There are thus three cases for the upper 

 and three for the lower boundary of the core, or with the primary cases ten 

 cases in all. Galton denotes the summit of the core on the central line of the 

 bulb by S, and the bottom of the core on the same central line by B. Then 

 the possible cases are 



= primary or arch ; 1 - WSV - WBV; 2 = SW-BV; 



Z = SV-BW; 4 = SV-BV; 5=WSV-BV; 



6 = SV-WBV- 7=SW-BW; 8=WSV-BW; 

 9 = SW-WBV. 



* Galton remarks: "There is usually quite enough length in a straight line of the upper- 

 most portion of the inner bend to indicate the direction of the required axis" (p. 9). I am less 

 confident of this. I should be inclined to replace Galton's axes by drawing a tangent from the 

 delta to the head of the loop, and taking this and the perpendicular to it through the point of 

 contact as the axis of reference, denning this perpendicular as the "loop axis." 



21—2 



