Finger Prints

by Francis Galton

3. “Method of Indexing Finger Marks.” Proc. Royal Society, vol. xlix. (1891).

4. “Identification by Finger Tips.” Nineteenth Century, August 1891.

This first and introductory chapter contains a brief and orderly summary of the contents of those that follow.

The second chapter treats of the previous employment of finger prints among various nations, which has been almost wholly confined to making daubs, without paying any regard to the delicate lineations with which this book is alone concerned. Their object was partly superstitious and partly ceremonial; superstitious, so far as a personal contact between the finger and the document was supposed to be of mysterious efficacy: ceremonial, as a formal act whose due performance in the presence of others could be attested. A few scattered instances are mentioned of persons who had made finger prints with enough care to show their lineations, and who had studied them; some few of these had used them as signatures. Attention is especially drawn to Sir William Herschel, who brought the method of finger prints into regular official employment when he was “Collector” or chief administrator of the Hooghly district in Bengal, and my large indebtedness to him is expressed in this chapter and in other places.

In the third chapter various methods of making good prints from the fingers are described at length, and more especially that which I have now adopted on a somewhat large scale, at my anthropometric laboratory, which, through the kindness of the authorities of South Kensington, is at present lodged in the galleries of their Science Collections. There, the ten digits of both hands of all the persons who come to be measured, are impressed with clearness and rapidity, and a very large collection of prints is steadily accumulating, each set being, as we shall see, a sign-manual that differentiates the person who made it, throughout the whole of his life, from all the rest of mankind.

Descriptions are also given of various methods of enlarging a finger print to a convenient size, when it is desired to examine it closely. Photography is the readiest of all; on the other hand the prism (as in a camera lucida) has merits of its own, and so has an enlarging pantagraph, when it is furnished with a small microscope and cross wires to serve as a pointer.

In the fourth chapter the character and purpose of the ridges, whose lineations appear in the finger print, are discussed. They have been the topic of a considerable amount of careful physiological study in late years, by writers who have investigated their development in early periods of unborn life, as well as their evolutionary history. They are perfectly defined in the monkeys, but appear in a much less advanced stage in other mammalia. Their courses run somewhat independently of the lines of flexure. They are studded with pores, which are the open mouths of ducts proceeding from the somewhat deeply-seated glands which secrete perspiration, so one of their functions is to facilitate the riddance of that excretion. The ridges increase in height as the skin is thickened by hard usage, until callosities begin to be formed, which may altogether hide them. But the way in which they assist the touch and may tend to neutralise the dulling effect of a thick protective skin, is still somewhat obscure. They certainly seem to help in the discrimination of the character of surfaces that are variously rubbed between the fingers.

These preliminary topics having been disposed of, we are free in the fifth chapter to enter upon the direct course of our inquiry, beginning with a discussion of the various patterns formed by the lineations. It will be shown how systems of parallel ridges sweep in bold curves across the palmar surface of the hand, and how, whenever the boundaries of two systems diverge, the interspace is filled up by a compact little system of its own, variously curved or whorled, having a fictitious resemblance to an eddy between two currents. An interspace of this kind is found in the bulb of each finger. The ridges run in parallel lines across the finger, up to its last joint, beyond which the insertion of the finger-nail causes a compression of the ridges on either side; their intermediate courses are in consequence so much broadened out that they commonly separate, and form two systems with an interspace between them. The independent patterns that appear in this interspace upon the bulbs of the fingers, are those with which this book is chiefly concerned.

At first sight, the maze formed by the minute lineations is bewildering, but it is shown that every interspace can be surely outlined, and when this is done, the character of the pattern it encloses, starts conspicuously into view. Examples are given to show how the outlining is performed, and others in which the outlines alone are taken into consideration. The cores of the patterns are also characteristic, and are described separately. It is they alone that have attracted the notice of previous inquirers. The outlines fall for the most part into nine distinct genera, defined by the relative directions of the divergent ridges that enclose them. The upper pair (those that run towards the finger-tip) may unite, or one or other of them may surmount the other, thus making three possibilities. There are three similar possibilities in respect to the lower pair; so, as any one of the first group may be combined with any one of the second, there are 3 × 3, or nine possibilities in all. The practice of somewhat rolling the finger when printing from it, is necessary in order to impress enough of its surface to ensure that the points at which the boundaries of the pattern begin to diverge, shall be always included.

Plates are given of the principal varieties of patterns, having regard only to their more fundamental differences, and names are attached for the convenience of description; specimens are also given of the outlines of the patterns in all the ten digits of eight different persons, taken at hazard, to afford a first idea of the character of the material to be dealt with. Another and less minute system of classification under three heads is then described, which is very useful for rough preliminary purposes, and of which frequent use is made further on. It is into Arches, Loops, and Whorls. In the Arches, there is no pattern strictly speaking, for there is no interspace; the need for it being avoided by a successive and regular broadening out of the ridges as they cross the bulb of the finger. In Loops, the interspace is filled with a system of ridges that bends back upon itself, and in which no one ridge turns through a complete circle. Whorls contain all cases in which at least one ridge turns through a complete circle, and they include certain double patterns which have a whorled appearance. The transitional cases are few; they are fully described, pictured, and classified. One great advantage of the rude A. L. W. system is that it can be applied, with little risk of error, to impressions that are smudged or imperfect; it is therefore very useful so far as it goes. Thus it can be easily applied to my own finger prints on the title-page, made as they are from digits that are creased and roughened by seventy years of life, and whose impressions have been closely clipped in order to fit them into a limited space.