In the case of the method by actual measure ments although only a small fraction of the total number of relations is noted, yet these are in numerical form and can be averaged and the results compared directly.
The principle on which the method by in vestigation of proportions of parts rests is that the spaces between various distinctive points of a signature bear numerical relations to each other, and to the heights of certain letters, which are constant within comparatively narrow limits whether the signature be written small or large.
The following illustration (Fig. 3) represents a small part of a letter written with pen and ink and photographed at an enlargement of 30 diameters: Another valuable individ uality in writings executed by means of pen and ink are the irregularities observed in the mar gins of the lines when examined under a suffi ciently high power of the microscope (about 120 diameters). How far this examination will en able one to identify an individual is not yet known, but it has been established that there are characters in the general disposition, num ber, arranrement and position of these serra tions, which remain comparatively constant in the writings of the same individual with differ ent pens, ink and paper, and under different mental and physical conditions, and which therefore cannot have other source than peculiar motions imparted to the writing instrument and writing fluid by the writer.
Tables for the de termination of the character of inks by qualitative chemical tests have been published by Robertson, Hofmann and others. To the same end
special devices have been made to solve questions relating to the composition of inks with out affecting the document or writing fluid: Doremus by means of the spectroscope, Frazer through absorption of light admitted to and re flected by the ink through colored prisms. Sharples has shown that an otherwise invisible record may be made visible through shorter or longer ex - ' posure to tne sensitive plate or the pnoto graphic camera, etc.
Chabot, The Handwriting of Junius Professionally with a preface and collateral evidence, by the Hon. Edward Twisleton (1871) ; Cross & Bevan, Text-Book of Paper-Making' (1888) ; S. Weir Mitchell, M. D., (Mary Reynolds: a Case of Double with a letter on the handwritings peculiar to each of the two states by Persifor Frazer). Transactions of the Col lege of Physicians of Philadelphia (April 4, 1888) ; Gal ton, of Blurred Finger-Prints) (1893) ; Persifor Frazer, liotics or the Study of Documents) (1894) ; Hagan, 'Disputed (1894) Ber tillon, 'La comparaison des ecritures et l'iden tification graphique) (Revue Scientifique, 18 Dec. 1897 and 1 Jan. 1898) ; Itasse, 'Le faux devant l'histoire, devant la science, et devant la loi) (1898); Persifor Frazer, 'Des faux en ecriture et de l'ecriture. Traduit par M. L. Vossion et Mme. H. Bouete (1899) ; Minovici, 'Les faux en icriture et la photographie au service de la justice' ; Ames, 'Forgery, its De tection and Illustration' (1900).