Great care is now taken officially to secure the correct order of fingers, as on that the validity of the method depends, and the whole utility of the classification.
Inspectors Stedman and Collins, in the work just quoted, state that when finger-prints are required to be produced as evidence in a court of justice, “they are first enlarged 5 diameters direct with an enlarging camera. The negatives are afterwards placed in an electric light enlarging lantern, with which it is possible to obtain a photographic enlargement of a finger-print 36 inches square, such a photograph being as large as is ever likely to be required.”
In my Guide to Finger-Print Identification (p. 62) I have advocated uniform enlargement of all such exhibits on the decimal or metric system, and hope that international agreement on this point may be secured. Apart from criminal services its scientific utility would ultimately be very great. The objection that an English jury would dislike being confronted with the technicalities of a foreign and “mathematical” system is very easily met. An English jury—and no jury in the world is fairer or clearer-headed—would only, in any case, have to compare two figures similarly enlarged, one being that of the accused person’s fingers, taken while in custody, and the other, either a similar official record of another date, or a smudgy mark from some blotting-pad, window-pane, drinking-glass, bottle, or the like. The two exhibits, paired for comparison, would have been enlarged exactly on the same scale, whatever that scale might have been. For purposes of judicial comparison, therefore, English terms and English instruments might be used throughout, and no inconvenience could be felt by the most insularly prejudiced jury that could possibly be got together.
When a photographic enlargement has been made, it is necessary to be able readily to test its conformity with the enlargement to be compared with it, or if there be not strict agreement, to allow for and calculate the admitted discrepancy. This may easily be done by an application of the “rule of three.”
Reduced Copy of Police Register Form
Reverse Side of Form
It may be necessary to test the concurrence of curved lines in two exhibits similarly enlarged. At one time I used strips of plumber’s lead, placed edgeways on the curved lines to be compared. They could be flexed so as to show the various sinuosities, however complex, but leaden tapes cannot readily be made to retain the form imparted to them. Copper wire I found to be stiffer, but it readily warps off the plane. An excellent way is to draw on transparent paper a line corresponding to the curved line seen underneath. The transparency is then transferred and adjusted to the other enlargement, the curves of which should be seen to be congruent. The instrument called “flexible curves” which is used by engineers and mechanical draughtsmen I at last tried, and found it to be exceedingly serviceable for such comparisons. The pattern “B,” self-clamping, 12-inch size, is for most cases the most suitable. Other patterns are made also, in sizes of 9 and 18 inches. The “B” pattern has a flexible steel strip, like the lead tape just mentioned. After the curve or series of sinuosities has been adjusted correctly, the shape is rigidly retained by means of a stiff-hinged link-work arrangement attached by tabs. The strip of steel should not be pressed down between two tabs, and when bending or straightening out the instrument one should do so bit by bit, beginning at one end and continuing onwards from there. This useful self-clamping instrument used to be supplied by Mr. Wm. Brooks, scientific instrument maker, 33 Fitzroy Street, Tottenham Court Road, London. Another instrument of this kind, the “Curve Rule” is sold by Mr. W. Harling, 47 Finsbury Pavement, E.C., and is figured here.
