SCIENCE IN" CRIME DETECTION — HOOVER 219 



that they have become an indispensable part of many routine exami- 

 nations. 



Immediately above the ultraviolet portion of the spectrum, there 

 appear in orderly sequence the visible colors ranging from violet 

 through extreme red, and inasmuch as these colors are directly in- 

 volved in the all-important process of vision, it obviously would be 

 futile to attempt, even in a much more comprehensive discussion than 

 space permits here, to touch upon more than a very few of the 

 applications to crime detection. Some of these, how^ever, are so 

 outstanding as to demand consideration. 



Foremost among these is the microscope as we know it today. 

 With these "seven-league glasses" it becomes possible for the expert 

 to ascertain whether the wisp of hair found clinging to the door 

 hinge of a suspected hit-and-run automobile is identical with com- 

 parison specimens of hair removed from the head of the child found 

 lying unconscious with a fractured skull at the edge of the road near 

 a small southern community; whether the printed fabric found 

 wrapped around a murdered victim's neck in another instance is 

 identical with similar fabric found at the home of a suspect; or 

 whether the stain appearing upon an ax recovered at the home of a 

 suspect is only rust, as claimed by the suspect, or is in fact a stain 

 caused by blood of human origin received when the ax was utilized 

 in a vicious attack on one of the suspect's neighbors. 



By adding polarizing elements to the microscope, the petrographer 

 is able to examine the colored interference patterns produced by 

 biref ringent crystalline materials and thereby determine, for example, 

 whether the soil removed from the shoes of a suspect is similar in 

 mineral content and structure to soil taken from the area where a 

 safe, which had been stolen from a mercantile store, had been forced 

 open and the contents looted. 



In the field of firearms identification, we find a somewhat different 

 modification of the microscope employed. Of several problems 

 which properly fall within the scope of this work, the principal one 

 deals with the examination of evidence — ^bullets and cartridge cases — 

 in an effort to ascertain whether they have been fired from a suspected 

 weapon recovered during the investigation. Such an examination is 

 based upon the existence on both bullet and cartridge case of many 

 minute markings, arising in the case of the bullet from its passage 

 over the microscopic imperfections present in the gun barrel, and in 

 the case of the shell from various imperfections in the breech face, 

 firing pin, and similar sources. It has been amply demonstrated 

 that each weapon creates a combination of such microscopic marks 

 which is not duplicated by any other weapon; accordingly, each 

 weapon, in effect, places its "fingerprint" upon all projectiles or shells 



