Finger Prints Part 2

The result is indicated by the diagram, which shows on what parts of the card the impressions fall. Thus each of the four fingers is impressed twice, once above with a simple dab, and once below with a rolled impression, but each thumb is only impressed once; the thumbs being more troublesome to print from than fingers. Besides, the cards would have to be made even larger than they are, if two impressions of each thumb had to be included. It takes from two and a half to three minutes to obtain the eighteen impressions that are made on each card.

The _pocket apparatus_ is similar to one originally made and used by Sir William J. Herschel (see Plate 3, Fig. 4, in which the roller and its bearings are drawn of the same size as those I use). A small cylinder of hard wood, or of bra.s.s tube, say 1-3/4 inch long, and 1/2 or 3/4 inch in diameter, has a pin firmly driven into each end to serve as an axle. A piece of tightly-fitting india-rubber tubing is drawn over the cylinder.

The cylinder, thus coated with a soft smooth compressible material, turns on its axle in two brackets, each secured by screws, as shown in Plate 2, Fig. 4, to a board (say 6 2-1/2 1/4 inch) that serves as handle. This makes a very fair and durable roller; it can be used in the heat and damp of the tropics, and is none the worse for a wetting, but it is by no means so good for delicate work as a cylinder covered with roller composition.

These are not at all difficult to make; I have cast them for myself. The mould is a piece of bra.s.s tube, polished inside. A thick disc, with a central hole for the lower pin of the cylinder, fits smoothly into the lower end of the mould, and a ring with a thin bar across it, fits over the other end, the upper pin of the cylinder entering a hole in the middle of the bar; thus the cylinder is firmly held in the right position. After slightly oiling the inside of the mould, warming it, inserting the disc and cylinder, and fitting on the ring, the melted composition is poured in on either side of the bar. As it contracts on cooling, rather more must be poured in than at first appears necessary. Finally the roller is pushed out of the mould by a wooden ramrod, applied to the bottom of the disc.

The composition must be melted like glue, in a vessel surrounded by hot water, which should never be allowed to boil; otherwise it will be spoilt.

Harrild's best composition is more than twice the cost of that ordinarily used, and is expensive for large rollers, but for these miniature ones the cost is unimportant. The mould with which my first roller was made, was an old pewter squirt with the nozzle cut off; its piston served the double purpose of disc and ramrod.

The _Slab_ is a piece of thick plate gla.s.s, of the same length and width as the handle to the roller, so they pack up easily together; its edges are ground to save the fingers and roller alike from being cut. (Porcelain takes the ink better than gla.s.s, but is not to be commonly found in the shops, of a convenient shape and size; a glazed tile makes a capital slab.) A collapsible tube of printer's ink, a few rags, and a phial of washing soda, complete the equipment (benzole may spoil india-rubber).

When using the apparatus, spread a newspaper on the table to prevent accident, have other pieces of newspaper ready to clean the roller, and to remove any surplus of ink from it by the simple process of rolling it on the paper. Take care that the washing soda is in such a position that it cannot be upset and ruin the polish of the table. With these precautions, the apparatus may be used with cleanliness even in a drawing-room. The roller is of course laid on its back when not in use.

My a.s.sistant has taken good prints of the three first fingers of the right hands of more than 300 school children, say 1000 fingers, in a few hours during the same day, by this apparatus. Hawksley, 357 Oxford Street, W., sells a neatly fitted-up box with all the necessary apparatus.

_Rougher arrangements._--A small ball made by tying chamois leather round soft rags, may be used in the absence of a roller. The fingers are inked from the ball, over which the ink has been evenly distributed, by dabbing it many times against a slab or plate. This method gives good results, but is slow; it would be intolerably tedious to employ it on a large scale, on all ten digits of many persons.

It is often desirable to obtain finger prints from persons at a distance, who could not be expected to trouble themselves to acquire the art of printing for the purpose of making a single finger print. On these occasions I send folding-cases to them, each consisting of two pieces of thin copper sheeting, fastened side by side to a slip of pasteboard, by bending the edges of the copper over it. The pasteboard is half cut through at the back, along the s.p.a.ce between the copper sheets, so that it can be folded like a reply post-card, the copper sheets being thus brought face to face, but prevented from touching by the margin of an interposed card, out of which the middle has been cut away. The two pieces of copper being inked and folded up, may then be sent by post. On arrival the ink is fresh, and the folders can be used as ordinary inked slabs.

(See also Smoke Printing, page 47.)

The fluidity of even a very thin layer of ink seems to be retained for an indefinite time if the air is excluded to prevent oxidisation. I made experiments, and found that if pieces of gla.s.s (photographic quarter plates) be inked, and placed face to face, separated only by narrow paper margins, and then wrapped up without other precaution, they will remain good for a year and a half.

A slight film of oxidisation on the surface of the ink is a merit, not a harm; it is cleaner to work with and gives a blacker print, because the ink clings less tenaciously to the finger, consequently more of it is transferred to the paper.

If a blackened plate becomes dry, and is re-inked without first being cleaned, the new ink will rob the old of some of its oxygen and it will become dry in a day or even less.

_Lithography._--Prints may be made on "transfer-paper," and thence transferred to stone. It is better not to impress the fingers directly upon the stone, as the print from the stone would be reversed as compared with the original impression, and mistakes are likely to arise in consequence. The print is re-reversed, or put right, by impressing the fingers on transfer-paper. It might sometimes be desirable to obtain rapidly a large number of impressions of the finger prints of a suspected person. In this case lithography would be easier, quicker, and cheaper than photography.

_Water Colours and Dyes._--The pads most commonly used with office stamps are made of variously prepared gelatine, covered with fine silk to protect the surface, and saturated with an aniline dye. If the surface be touched, the finger is inked, and if the circ.u.mstances are all favourable, a good print may be made, but there is much liability to blot. The pad remains ready for use during many days without any attention, fresh ink being added at long intervals. The advantage of a dye over an ordinary water colour is, that it percolates the silk without any of its colour being kept back; while a solution of lampblack or Indian ink, consisting of particles of soot suspended in water, leaves all its black particles behind when it is carefully filtered; only clear water then pa.s.ses through.

A serviceable pad may be made out of a few thicknesses of cloth or felt with fine silk or cambric stretched over it. The ink should be of a slowly drying sort, made, possibly, of ordinary ink, with the admixture of brown sugar, honey, glycerine or the like, to bring it to a proper consistence.

Mr. Gilbert Thompson's results by this process have already been mentioned. A similar process was employed for the Bengal finger prints by Sir W. Herschel, who sent me the following account: "As to the printing of the fingers themselves, no doubt practice makes perfect. But I took no pains with my native officials, some dozen or so of whom learnt to do it quite well enough for all practical purposes from Bengali written instructions, and using nothing but a kind of lampblack ink made by the native orderly for use with the office seal." A batch of these impressions, which he was so good as to send me, are all clear, and in most cases very good indeed. It would be easier to employ this method in a very damp climate than in England, where a very thin layer of lampblack is apt to dry too quickly on the fingers.

_Printing as from Engraved Plates._--Professor Ray Lankester kindly sent me his method of taking prints with water colours. "You take a watery brushful or two of the paint and rub it over the hands, rubbing one hand against the other until they feel sticky. A _thin_ paper (tissue is best) placed on an oval cushion the shape of the hand, should be ready, and the hand pressed not too firmly on to it. I enclose a rough sample, done without a cushion. You require a cushion for the hollow of the hand, and the paint must be rubbed by the two hands until they feel sticky, not watery." This is the process of printing from engravings, the ink being removed from the ridges, and lying in the furrows. Blood can be used in the same way.

The following is extracted from an article by Dr. Louis Robinson in the _Nineteenth Century_, May 1892, p. 303:--

"I found that direct prints of the infant's feet on paper would answer much better [than photography]. After trying various methods I found that the best results could be got by covering the foot by means of a soft stencil brush with a composition of lampblack, soap, syrup, and blue-black ink; wiping it gently from heel to toe with a smoothly-folded silk handkerchief to remove the superfluous pigment, and then applying a moderately flexible paper, supported on a soft pad, direct to the foot."

A curious method with paper and ordinary writing ink, lately contrived by Dr. Forgeot, is a.n.a.logous to lithography. He has described in one of the many interesting pamphlets published by the "Laboratoire d'Anthropologie Criminelle" of Lyon (_Stenheil_, 2 Rue Casimir-Delavigne, Paris), his new process of rendering visible the previously invisible details of such faint finger prints as thieves may have left on anything they have handled, the object being to show how evidence may sometimes be obtained for their identification. It is well known that pressure of the hand on the polished surface of gla.s.s or metal leaves a latent image very difficult to destroy, and which may be rendered visible by suitable applications, but few probably have suspected that this may be the case, to a considerable degree, with ordinary paper. Dr. Forgeot has shown that if a slightly greasy hand, such for example as a hand that has just been pa.s.sed through the hair, be pressed on clean paper, and if common ink be afterwards brushed lightly over the paper, it will refuse to lie thickly on the greasy parts, and that the result will be a very fair picture of the minute markings on the fingers. He has even used these productions as negatives, and printed good photographs from them. He has also sent me a photographic print made from a piece of gla.s.s which had been exposed to the vapour of hydrofluoric acid, after having been touched by a greasy hand. I have made many trials of his method with considerable success. It affords a way of obtaining serviceable impressions in the absence of better means. Dr. Forgeot's pamphlet describes other methods of a generally similar kind, which he has found to be less good than the above.

_Smoke Printing._--When other apparatus is not at hand, a method of obtaining very clear impressions is to smoke a plate over a lighted candle, to press the finger on the blackened surface, and then on an adhesive one. The following details must, however, be borne in mind: the plate must not be smoked too much, for the same reason that a slab must not be inked too much; and the adhesive surface must be only slightly damped, not wetted, or the impression will be blurred. A crockery plate is better than gla.s.s or metal, as the soot does not adhere to it so tightly, and it is less liable to crack. Professor Bowditch finds mica (which is sold at photographic stores in small sheets) to be the best material.

Certainly the smoke comes wholly off the mica on to the parts of the finger that touch it, and a beautiful negative is left behind, which can be utilised in the camera better than gla.s.s that has been similarly treated; but it does not serve so well for a plate that is intended to be kept ready for use in a pocket-book, its softness rendering it too liable to be scratched. I prefer to keep a slip of very thin copper sheeting in my pocket-book, with which, and with the gummed back of a postage stamp, or even the gummed fringe to a sheet of stamps, impressions can easily be taken. The thin copper quickly cools, and a wax match supplies enough smoke. The folders spoken of (p. 42) may be smoked instead of being inked, and are in some cases preferable to carry in the pocket or to send by post, being so easy to smoke afresh. Luggage labels that are thickly gummed at the back furnish a good adhesive surface. The fault of gummed paper lies in the difficulty of damping it without its curling up. The gummed paper sold by stationers is usually thinner than luggage labels, and still more difficult to keep flat. Paste rubbed in a very thin layer over a card makes a surface that holds soot firmly, and one that will not stick to other surfaces if accidentally moistened. Glue, isingla.s.s, size, and mucilage, are all suitable. It was my fortune as a boy to receive rudimentary lessons in drawing from a humble and rather grotesque master.

He confided to me the discovery, which he claimed as his own, that pencil drawings could be fixed by licking them; and as I write these words, the image of his broad swab-like tongue performing the operation, and of his proud eyes gleaming over the drawing he was operating on, come vividly to remembrance. This reminiscence led me to try whether licking a piece of paper would give it a sufficiently adhesive surface. It did so. Nay, it led me a step further, for I took two pieces of paper and licked both.

The dry side of the one was held over the candle as an equivalent to a plate for collecting soot, being saved by the moisture at the back from igniting (it had to be licked two or three times during the process), and the impression was made on the other bit of paper. An ingenious person determined to succeed in obtaining the record of a finger impression, can hardly fail altogether under any ordinary circ.u.mstances.

Physiologists who are familiar with the revolving cylinder covered with highly-glazed paper, which is smoked, and then used for the purpose of recording the delicate movements of a tracer, will have noticed the beauty of the impression sometimes left by a finger that had accidentally touched it. They are also well versed in the art of varnishing such impressions to preserve them in a durable form.

A cake of blacklead (plumbago), such as is sold for blackening grates, when rubbed on paper leaves a powdery surface that readily blackens the fingers, and shows the ridges distinctly. A small part of the black comes off when the fingers are pressed on sticky paper, but I find it difficult to ensure good prints. The cakes are convenient to carry and cleanly to handle. Whitening, and still more, whitening mixed with size, may be used in the same way, but it gathers in the furrows, not on the ridges.

_Casts_ give undoubtedly the most exact representation of the ridges, but they are difficult and unsatisfactory to examine, puzzling the eye by showing too conspicuously the variation of their heights, whereas we only want to know their courses. Again, as casts must be of a uniform colour, the finer lines are indistinctly seen except in a particular light.

Lastly, they are both c.u.mbrous to preserve and easily broken.

A sealing-wax impression is the simplest and best kind of cast, and the finger need not be burnt in making it. The plan is to make a considerable pool of flaming sealing-wax, stirring it well with the still unmelted piece of the stick, while it is burning. Then blow out the flame and wait a little, until the upper layer has cooled. Sealing-wax that has been well aflame takes a long time to harden thoroughly after it has parted with nearly all its heat. By selecting the proper moment after blowing out the flame, the wax will be cool enough for the finger to press it without discomfort, and it will still be sufficiently soft to take a sharp impression. Dentist's wax, which is far less brittle, is easily worked, and takes impressions that are nearly as sharp as those of sealing-wax; it has to be well heated and kneaded, then plunged for a moment in cold water to chill the surface, and immediately impressed. Gutta-percha can also be used. The most delicate of all impressions is that left upon a thick clot of varnish, which has been exposed to the air long enough for a thin film to have formed over it. The impression is transient, but lingers sufficiently to be easily photographed. It happened, oddly enough, that a few days after I had noticed this effect, and had been experimenting upon it, I heard an interesting memoir "On the Minute Structure of Striped Muscle, with special allusion to a new method of investigation by means of 'Impressions' stamped in Collodion," submitted to the Royal Society by Dr. John Berry Haycraft, in which an a.n.a.logous method was used to obtain impressions of delicate microscopic structures.

_Photographs_ are valuable in themselves, and the negatives serve for subsequent _enlargements_. They are unquestionably accurate, and the labour of making them being mechanical, may be delegated. If the print be in printer's ink on white paper, the process is straightforward, first of obtaining a negative and afterwards photo-prints from it. The importance of the paper or card used to receive the finger print being quite white, has already been pointed out. An imprint on white crockery-ware is beautifully clear. Some of the photographs may be advantageously printed by the ferro-prussiate process. The paper used for it does not curl when dry, its texture is good for writing on, and the blue colour of the print makes handwriting clearly legible, whether it be in ink or in pencil.

Prints on gla.s.s have great merits for use as lantern slides, but it must be recollected that they may take some days to dry, and that when dry the ink can be only too easily detached from them by water, which insinuates itself between the dry ink and the gla.s.s. Of course they could be varnished, if the trouble and cost were no objection, and so preserved.

The negative print left on an inked slab, after the finger has touched it, is sometimes very clear, that on smoked gla.s.s better, and on smoked mica the clearest of all. These have merely to be placed in the enlarging camera, where the negative image thrown on argento-bromide paper will yield a positive print. (See p. 90.)

I have made, by hand, many enlargements with a prism (camera lucida), but it is difficult to enlarge more than five times by means of it. So much shade is cast by the head that the prism can hardly be used at a less distance than 3 inches from the print, or one quarter the distance (12 inches) at which a book is usually read, while the paper on which the drawing is made cannot well be more than 15 inches below the prism; so it makes an enlargement of (4 15)/12 or five-fold. This is a very convenient method of a.n.a.lysing a pattern, since the lines follow only the axes of the ridges, as in Plate 3, Fig. 5. The prism and attached apparatus may be kept permanently mounted, ready for use at any time, without the trouble of any adjustment.

An enlarging pantagraph has also been of frequent use to me, in which the cross-wires of a low-power microscope took the place of the pointer. It has many merits, but its action was not equally free in all directions; the enlarged traces were consequently jagged, and required subsequent smoothing.

All hand-made enlargements are tedious to produce, as the total length of lineations to be followed is considerable. In a single finger print made by dabbing down the finger, their actual length amounts to about 18 inches; therefore in a five-fold enlargement of the entire print the pencil has to be carefully directed over five times that distance, or more than 7 feet.

Large copies of tracings made on transparent paper, either by the Camera Lucida or by the Pantagraph, are easily printed by the ferro-prussiate photographic process mentioned above, in the same way that plans are copied by engineers.

CHAPTER IV

THE RIDGES AND THEIR USES

The palmar surface of the hands and the soles of the feet, both in men and monkeys, are covered with minute ridges that bear a superficial resemblance to those made on sand by wind or flowing water. They form systems which run in bold sweeps, though the courses of the individual ridges are less regular. Each ridge (Plate 3, Fig. 5) is characterised by numerous minute peculiarities, called _Minutiae_ in this book, here dividing into two, and there uniting with another (_a_, _b_), or it may divide and almost immediately reunite, enclosing a small circular or elliptical s.p.a.ce (_c_); at other times its beginning or end is markedly independent (_d_, _e_); lastly, the ridge may be so short as to form a small island (_f_).

Whenever an inters.p.a.ce is left between the boundaries of different systems of ridges, it is filled by a small system of its own, which will have some characteristic shape, and be called a _pattern_ in this book.

[Ill.u.s.tration: PLATE 3.

FIG. 5. Characteristic peculiarities in Ridges (about 8 times the natural size).

FIG. 6. Systems of Ridges, and the Creases in the Palm.]

There are three particularly well-marked systems of ridges in the palm of the hand marked in Plate 3, Fig. 6, ~1~, as Th, AB, and BC. The system Th is that which runs over the ball of the thumb and adjacent parts of the palm. It is bounded by the line _a_ which starts from the middle of the palm close to the wrist, and sweeps thence round the ball of the thumb to the edge of the palm on the side of the thumb, which it reaches about half an inch, more or less, below the base of the fore-finger. The system AB is bounded towards the thumb by the above line _a_, and towards the little finger by the line _b_; the latter starts from about the middle of the little-finger side of the palm, and emerges on the opposite side just below the fore-finger. Consequently, every ridge that wholly crosses the palm is found in AB. The system BC is bounded thumbwards by the line _b_, until that line arrives at a point immediately below the axis of the fore-finger; there the boundary of BC leaves the line _b_, and skirts the base of the fore-finger until it reaches the interval which separates the fore and middle fingers. The upper boundary of BC is the line _c_, which leaves the little-finger side of the palm at a small distance below the base of the little finger, and terminates between the fore and middle fingers. Other systems are found between _c_ and the middle, ring, and little fingers; they are somewhat more variable than those just described, as will be seen by comparing the five different palms shown in Fig. 6.

An interesting example of the interpolation of a small and independent system occurs frequently in the middle of one or other of the systems AB or BC, at the place where the s.p.a.ce covered by the systems of ridges begins to broaden out very rapidly. There are two ways in which the necessary supply of ridges makes its appearance, the one is by a series of successive embranchments (Fig. 6, ~1~), the other is by the insertion of an independent system, as shown in ~4~, ~5~. Another example of an interpolated system, but of rarer occurrence, is found in the system Th, on the ball of the thumb, as seen in ~2~.

Far more definite in position, and complex in lineation, are the small independent systems which appear on the bulbs of the thumb and fingers.

They are more instructive to study, more easy to cla.s.sify, and will alone be discussed in this book.

In the diagram of the hand, Fig. 6, ~1~, the three chief cheiromantic creases are indicated by dots, but are not numbered. They are made (1) by the flexure of the thumb, (2) of the four fingers simultaneously, and (3) of the middle, ring, and little fingers simultaneously, while the fore-finger remains extended. There is no exact accordance between the courses of the creases and those of the adjacent ridges, less still do the former agree with the boundaries of the systems. The accordance is closest between the crease (1) and the ridges in Th; nevertheless that crease does not agree with the line _a_, but usually lies considerably within it. The crease (2) cuts the ridges on either side, at an angle of about 30 degrees. The crease (3) is usually parallel to the ridges between which it runs, but is often far from accordant with the line _c_. The creases at the various joints of the thumb and fingers cut the ridges at small angles, say, very roughly, of 15 degrees.

The supposition is therefore untenable that the courses of the ridges are wholly determined by the flexures. It appears, however, that the courses of the ridges and those of the lines of flexure may be in part, but in part only, due to the action of the same causes.

The fact of the creases of the hand being strongly marked in the newly-born child, has been considered by some to testify to the archaic and therefore important character of their origin. The crumpled condition of the hand of the infant, during some months before its birth, seems to me, however, quite sufficient to account for the creases.