Science and the Criminal

by C. Ainsworth Mitchell

The present writer, however, has been unable to confirm these statements. It is true that differences in intensity appear upon the negative, but these are not any more pronounced than the differences obvious to the eye in the writing, and the use of special plates and screens does not give any more satisfactory results.

The chief use of the photographic methods is to distinguish differences in form rather than in colour, and to record them for purposes of demonstration.

One direction in which photography is particularly useful is in deciphering the words in faded ink upon old documents, for the yellow colour of the ancient vellum is due to the formation of iron oxide.

Of recent years photography has supplied another valuable means of detecting alterations in documents, and it has been found particularly useful for demonstrating to a judge and jury the results of a microscopical examination.

Photographic reproduction and enlargement has the advantage over chemical methods of not producing any alteration in the ink or paper, and in some instances is just as effective as the latter. In the examination of wills, for instance, it is necessary to obtain the express permission of the President of the Probate Court, before any chemical tests may be applied to the document, and except under special circumstances such permission would certainly be refused.

All the details of the writing and of the texture of the paper may be recorded by the camera, and a photographic enlargement may then be made to any required extent, so as to obtain what practically amounts to a record of the microscopical appearance. And the process has the additional advantage over microscopical examination that a large portion of the magnified surface may be examined at the same time, whereas in studying a document under the microscope, the view is restricted to a very minute portion of the surface.

With the more general use of the typewriter it became possible to write libellous letters with much less risk of detection than in the case of letters written in ordinary pen and ink, for the machine eliminates the personal characteristics of the writer.

The differences between various makes of typing ink are also less pronounced than the differences between different kinds of writing ink, and the proof of the identical character of two inks has, therefore, usually less significance.

There are, however, certain typewriting inks, which are characteristic from the fact that they contain finely-divided carbon, and are, therefore, unlike most typing inks, exceedingly permanent, and it is also possible to distinguish between the more common violet aniline inks by the different degrees of resistance that they offer to bleaching reagents.

Although it is not possible to identify the writer of a typed document by a study of the typing it is frequently not a difficult matter with the aid of the microscope to identify the machine upon which it was written.