Personal Identification and Description 171
It appears, possibly for reasons to which we have already referred (see p. 163), that Galton had by this time put aside his earlier method of indexing, and he remarks
" Without caring to dwell on many of my earlier failures to index the finger-prints in a satisfactory way, my description shall be confined to that which has proved to be a success. It is based on a small variety of conspicuous differences of pattern in each of many digits, and not upon minute peculiarities of a single digit." (p. 541.)
Galton had now obtained the prints of all ten digits of 289 persons, though his indexing applies only to the first hundred of these.
He here introduces for the first time the Arch-Loop-Whorl classification*, which has formed the basis of all later attempts at indexing. If a line be drawn from the tip of the forefinger to the base of the little finger, this is roughly the usual slope of the " axes " of the finger-prints if they be not symmetrical. Galton uses the odd numerals 1, 3, 5 for symmetrical forms or for sloped forms with the usual or "normal" slope, the even numerals 2, 4, 6 for the unusual or "abnormal" slopes, in the three classes, arches, loops, whorls. There is little difficulty as a rule in allotting a print to one or other of these six classes. It is only when the rarer compounds (later termed "composites") appear that some difficulty may arise. Galton's scheme is provided in the accompanying diagram.
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He does not arrange his numerals which denote the character of the finger-print in the natural order of the digits, i.e. from little finger left to little finger right. His reason for this is thus stated:,
"The forefingers are the most variable of all the digits in respect to their patterns, their slopes being almost as frequently abnormal as not t; the third fingers rank next ; the little finger .ranks last, as its pattern is a loop in nine cases out of ten. I, therefore, found it convenient not to index the fingers in their natural order, but in the way that is shown at the head of the
* Galton still uses the term "primary" for arch. f i.e. as frequently radial as ulnar.