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- 
mule 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 
