The evidence that the minutiæ persist throughout life is derived from the scrutiny and comparison of various duplicate impressions, one of each pair having been made many years ago, the other recently. Those which I have studied more or less exhaustively are derived from the digits of fifteen different persons. In some cases repeated impressions of one finger only were available; in most cases of two fingers; in some of an entire hand. Altogether the whole or part of repeated impressions of between twenty and thirty different digits have been studied. I am indebted to Sir W. J. Herschel for almost all these valuable data, without which it would have been impossible to carry on the inquiry. The only other prints are those of Sir W. G——, who, from curiosity, took impressions of his own fingers in sealing-wax in 1874, and fortunately happened to preserve them. He was good enough to make others for me last year, from which photographic prints were made. The following table gives an analysis of the above data. It would be well worth while to hunt up and take the present finger prints of such of the Hindoos as may now be alive, whose impressions were taken in India by Sir W. J. Herschel, and are still preserved. Many years must elapse before my own large collection of finger prints will be available for the purpose of testing persistence during long periods.
The pattern in every distinct finger print, even though it be only a dabbed impression, contains on a rough average thirty-five different points of reference, in addition to its general peculiarities of outline and core. They consist of forkings, beginnings or ends of ridges, islands, and enclosures. These minute details are by no means peculiar to the pattern itself, but are distributed with almost equal abundance throughout the whole palmar surface. In order to make an exhaustive comparison of two impressions they ought to be photographically enlarged to a size not smaller than those shown in [Plate 15]. Two negatives of impressions can thus be taken side by side on an ordinary quarter-plate, and any number of photographic prints made from them; but, for still more comfortable working, a further enlargement is desirable, say by the prism, [p. 52]. Some of the prints may be made on ferro-prussiate paper, as already mentioned [pp. 51], [53]; they are more convenient by far than prints made by the silver or by the platinum process.
Having placed the enlarged prints side by side, two or three conspicuous and convenient points of reference, whether islands, enclosures, or particularly distinct bifurcations, should be identified and marked. By their help, the position of the prints should be readjusted, so that they shall be oriented exactly alike. From each point of reference, in succession, the spines of the ridges are then to be followed with a fine pencil, in the two prints alternately, neatly marking each new point of comparison with a numeral in coloured ink ([Plate 13]). When both of the prints are good and clear, this is rapidly done; wherever the impressions are faulty, there may be many ambiguities requiring patience to unravel. At first I was timid, and proceeded too hesitatingly when one of the impressions was indistinct, making short alternate traces. Afterwards on gaining confidence, I traced boldly, starting from any well-defined point of reference and not stopping until there were reasonable grounds for hesitation, and found it easy in this way to trace the unions between opposite and incompletely printed ends of ridges, and to disentangle many bad impressions.
An exact correspondence between the details of two minutiæ is of secondary importance. Thus, the commonest point of reference is a bifurcation; now the neck or point of divergence of a new ridge is apt to be a little low, and sometimes fails to take the ink; hence a new ridge may appear in one of the prints to have an independent origin, and in the other to be a branch. The apparent origin is therefore of little importance, the main fact to be attended to is that a new ridge comes into existence at a particular point; how it came into existence is a secondary matter. Similarly, an apparently broken ridge may in reality be due to an imperfectly printed enclosure; and an island in one print may appear as part of an enclosure in the other. Moreover, this variation in details may be the effect not only of imperfect inking or printing, but of disintegration due to old age, which renders the impressions of the ridges ragged and broken, as in my own finger prints on the title-page.
[Plate 11], Fig. 18 explains the nature of the apparent discrepancies better than a verbal description. In a a new ridge appears to be suddenly intruded between two adjacent ones, which have separated to make room for it; but a second print, taken from the same finger, may have the appearance of either b or c, showing that the new ridge is in reality a fork of one or other of them, the low connecting neck having failed to leave an impression. The second line of examples shows how an enclosure which is clearly defined in d may give rise to the appearance of broken continuity shown in e, and how a distinct island f in one of the prints may be the remnant of an enclosure which is shown in the other. These remarks are offered as a caution against attaching undue importance to disaccord in the details of the minutiæ that are found in the same place in different prints. Usually, however, the distinction between a fork and the beginning of a new ridge is clear enough; the islands and enclosures are also mostly well marked.
PLATE 13.
Fig. 20.
V. H. H-D æt. 2½ in 1877, and again as a boy in Nov. 1890.
| 1r 1887 V. H. H-d | 1r 1890 V. H. H-d |
| 3r 1887 V. H. H-d | 3r 1890 V. H. H-d |