The possible variations in such a classification of the impressions of the three fingers of the right hand cannot exceed thirty-six, and a thousand prints may therefore be indexed into one of these thirty-six groups. Subdivisions of these main groups may then be based upon the characteristics of the prints of the fingers of the other hand and of the thumbs, while differences in the cores of the patterns afford a means of forming smaller divisions of the loop patterns.
From observations of the 5,000 prints of 500 individuals Sir Francis Galton found that arches were present in 6·5 per cent.; loops in 67·5 per cent.; and whorls in 26·0 per cent. Each digit and hand, however, had its own peculiarities, and the variations in the percentage of arches upon different digits ranged from 1 to 17; that of the loops from 53 to 90; and that of the whorls from 13 to 45.
Loops occurred with most frequency upon the little finger and then upon the middle finger, while whorls were rarely met with upon these fingers, but were of common occurrence upon the thumb and ring finger.
The classification employed by the English police was devised by Sir Edward Henry and is a modification of that of Sir Francis Galton, from which it differs in making use of four types instead of three. The impressions are grouped into arches, loops, whorls, and composites. The last group includes patterns made up of combinations of the other three, or those which might be classified either as loops or whorls. There are also numerous subdivisions of the group into patterns with characteristics in common such as “central pockets” and “accidentals,” and further differentiation is effected by counting the number of ridges between two fixed points in the patterns.
Examples of these four groups are shown in the plate facing [p. 66].
Dr. Faulds, who, while at a hospital in Japan, made an exhaustive study of the finger impressions of the Japanese, appears to have been the first to suggest the possibility of tracing a criminal by the imprints of his fingers upon external objects.
He mentions two instances where the method had afforded valuable evidence, and these are worth recording as early examples of the use of the system in detective work.
TYPES OF FINGER PRINTS
In one case some rectified spirit had been drunk, and the greasy marks of the fingers upon the bottle plainly showed who was the culprit, for their pattern was identical with that of an imprint in Dr. Fauld’s collection.