FORENSIC MICROSCOPY. 137 



of the finger the outer ridges, the loop, and the basal 

 ridges ■will cut off between them a triangle, known as 

 the delta (2, Fig. 51); this is the loop type. Finally, 

 the ridges on the bulb may be so twisted as to form a 

 complete circle cutting off two deltas, one on either side; 

 this is the whorl type (3, Fig. 51). 



A classification of the ten digits according to their 

 arches, loops, and whorls serves for a primary division 

 of finger-print cards into a number of general classes. 

 Since, however, certain combinations of these digital for- 

 mulae are much more common than others, further sub- 

 division must be made ; and this may be accomplished by 

 studying the minuter structures of the finger-print, and 

 particularly by counting the ridges in the loops of those 

 digits which show that structure. It is here that the 

 microscope comes into play, since such details cannot 

 well be made out with the naked eye. A magnification 

 of only ten or twenty diameters is, however, generally de- 

 sirable; hence the instrument used must be either a simple 

 microscope, preferably mounted on a stand, or a com- 

 pound microscope of very low power and very wide field. 



5. The Examination of Documents. — ^In the study of 

 disputed documents the microscope may be of considera- 

 ble service to the legal expert. The material of which 

 paper is made, its texture and sizing, and its water-marks 

 should first be noted, the character of the writing instru- 

 ment and the grooves it cuts upon the paper, if a steel 

 pen, being possibly significant. Inks may be tested by 

 various chemical methods; but much may be learned 

 under the microscope from an observation of the color 



