At Scotland Yard a metallic brace is in use for the purpose of forcing
refractory prisoners to leave correct impressions upon the records.
One application of this brace is persuasive enough to cause the
culprit to hasten to comply with a request for his signature.
A small slab stone is covered with ink, which is distributed with a
sprayer, and the prisoner is compelled to place his fingers in the ink
and then firmly implant them upon paper.
On a regular prescribed form impressions are taken so that the flexure
of the last joint shall be at a given point on the record.
The digits are taken singly and then an imprint is made of all of them
simultaneously.
When the prisoner has finished imprinting the record he is called upon
for his signature, and immediately underneath the name, as written by
himself, an imprint is left of the right forefinger.
For the edification of American police, Mr. Ferrier demonstrates that
upon a sheet of paper you may sprinkle some charcoal dust and press
it upon the paper with your thumb and then blow the dust off and the
imprint of the digit will remain.