Thumb or finger-prints are absolutely serviceable and certain in the detection of crime or in establishing a person’s identity.

That this system may be most effectively employed as an adjunct to the rogue’s gallery for fixing the identity of criminals there can be no doubt, since, from various experiments made it has been demonstrated that impressions made from the dermal furrows of the thumb or finger of no two persons can be sufficiently identical, when inspected under a microscope, to be mistaken one for the other; and that it is a powerful agency for the detection of criminals.

Very often, on the scene of a crime, finger marks are found on glossy surfaces (bottles, glasses, window panes, door plates, painted and varnished walls, etc.).  By a comparison of such impressions, photographed by a special process, it is easy either to discover the maker of the finger marks observed at the scene of the crime, or to establish the innocence of a suspected person whose digital impressions have nothing in common with those marks.

Note and study fac-simile impressions of thumb-prints and finger-prints in Appendix at end of this book.

CHAPTER XI

DETECTING FORGERY WITH THE MICROSCOPE

Determining Questionable Signatures By the Aid of a Microscope—­A
Magnifying Glass Not Powerful Enough—­Character of Ink Easily
Told—­The Microscope and a Knowledge of Its Use—­Experience and
Education of an Examiner of Great Assistance—­An Expert’s Opinion—­The
Use of the Microscope Recommended—­Illustrating a Method of
Forgery—­What a Microscopic Examination Reveals—­How to Examine Forged
Handwriting with a Microscope—­Experts and a Jury—­What the Best
Authorities Recommend.

In all examinations of questioned signatures to determine the individual habit of the writer the use of the compound microscope is a necessity to obtain the best field for study and analysis for the reason that the most important details are often so minute that they cannot be seen with the naked eye in sufficient size to determine their individual character and accuracy.  A magnifying glass has but a limited field in this class of work, for it is not easily held in position steadily for continued observation and study, besides it has not the requisite power for the work.  The lower powers of the compound microscope are but available for the examination of signatures for the reason that when the higher powers are used but little of the signature is in the field of vision, although the power of the lens may be increased when some particular point or feature in the writing requires greater enlargement for more perfect definition.  The higher powers of the microscope are sometimes used to ascertain the character of inks with which the writing is done, and also to determine the character of the paper on which a signature is written, which at times becomes important.  For all practical uses of the microscope in the examination of signatures the range of object enlargement occurring between a three-inch and an inch objective will be found to answer the purpose, as the various powers of the lenses become important in making the analysis.