Science and the Criminal

by C. Ainsworth Mitchell

The principle underlying such identification is that the letters upon a new typewriter are arranged at very nearly equal spaces from each other and produce a fully horizontal line of writing. But after being in use for a very short period some of the letters are certain to get out of alignment, and to give faults in their relative position, which are usually reproduced every time those letters are struck. Thus, for instance, an “a” may be a little above the line and an “r” fall too much to the right, and these peculiarities will almost invariably recur throughout every scrap of writing done upon that machine, until the alignment has been adjusted. In no two machines are exactly the same variations in the relative positions of the different letters likely to occur. The chances of this happening is exceedingly remote, for there are some seventy letters and signs upon a typewriter.

A practical illustration of the value of the evidence thus afforded, was seen in a case that occurred about a year ago. It was suspected that a letter had been written in collusion with a clerk in a certain office, and proof of this was thought likely to have considerable influence upon the issue of the trial.

When this letter, which was in typewriting, was compared with another letter that had unquestionably been written in that office it was found that the faults of alignment in both were identical. Wherever a letter, or combination of letters, in the one fell above or below the line, the same thing occurred in the other, and wherever there was unequal spacing between two letters the distances were invariably equal in both cases.

In addition to this, the ink, which was of the violet type, contained the same pigment, and the watermarks on the two sheets of paper were the same.

There could, therefore, be no reasonable doubt as to the two letters having been written upon the same machine. As a matter of fact, this proof of collusion did not carry the weight that had been expected, for the case was decided upon issues that were not affected by such proof.

With the aid of a measuring-scale upon the eyepiece of the microscope it is possible to measure the thickness of strokes of writing only ten thousands of an inch across, and in some cases to prove in this way that a certain part of a document was written at a different time or with a different pen than the remainder of the writing.

In attempting to reproduce a signature a forger will probably make a preliminary outline with a blacklead pencil and then go over this with ink.

The imperfect removal of the pencil marks may then betray the fraud, as in the Whalley will case described on another page. In some instances the particles of the graphite may be seen with the aid of the microscope to project beyond the upper layer of ink.

Additions and alterations made to the letters in writing are clearly visible when magnified, and may be demonstrated in court by means of a photographic enlargement. Any irregularities in the edges of the letters or any break between one part of a letter and another appear much more pronounced when examined in this way, for all faults are enormously intensified. Thus the figure “0” might be altered into “9” by the addition of a stroke, or a “3” turned into an “8,” but it would be practically impossible to do this in such a manner as not to show when slightly magnified.

The accompanying illustrations, for which the writer is indebted to Mr. A. S. Osborn and the proprietors of Knowledge, will make these points clearer. In Fig. A is shown the result of an attempt to change the number “11” into “17” by the addition of a stroke to the top of the second “1.” The small inset represents the appearance of the fraudulent alteration, while beneath it is seen the microscopical enlargement, in which the joining of the added portion is plainly visible.