SCIENCE IN CRIME DETECTION — HOOVER 217 



result of a gradual development in several allied fields. However, 

 by noting the relation and application of various portions of the 

 electromagnetic radiant energy spectrum to specific crime detection 

 problems it is believed that a fairly representative, even if necessarily 

 somewhat brief and incomplete, picture of the subject as a whole 

 may be presented. 



Leaving the fascinating subject of spectrographic analj'sis which 

 in its broadest sense may encompass a relatively large portion of the 

 spectrum, and disregarding possible application of cosmic and radio- 

 active gamma radiation which at the present are of little more than 

 academic interest in relation to crime detection, there is found at 

 the short wave length end of the spectrum a powerful ally to law- 

 enforcement work in the X-ray. Probably the most important use 

 to which this valuable aid is put in police work lies in its application 

 to the examination of packages suspected of containing explosives. 

 Each year finds its quota of persons horribly mutilated or of homes 

 and business establishments wrecked bj^ such bombs, and the problem 

 confronting the oflScer who is charged with the responsibility of 

 investigating and destroying these weapons of a crazed mind is a 

 very real one. Fortunately, it is now possible in many instances 

 through the agency of the X-ray to ascertain the contents of a sus- 

 pected package without opening or otherwise disturbing the package 

 in any way, thereby permitting appropriate action to be taken in 

 the event the parcel is actually found to contain dangerous explosives. 



Plate 1, figure 1, is an X-ray photograph taken of a model bomb 

 showing the possibility of tracing the ignition wiring thus permitting 

 the bomb to be opened harmlessly. Plate 1, figure 2, on the other 

 hand, is an X-ray of a package received by a high Government official 

 and suspected of containing explosives, but found as indicated to 

 contain onlj^ a gavel presented by an admiring constituent, much to 

 the relief of the recipient. 



Above the X-rays in the radiant energy spectrum there is found 

 a type of radiation known as ultraviolet light, so named, of course, 

 because of its relation to the violet end of the visible spectrum which 

 will be discussed later. This portion of the spectrum, in addition to 

 exhibiting in general different selective reflection and transmission 

 characteristics from those encountered in the visible region, further 

 possesses the ability to excite to a state of luminescence many ma- 

 terials which are normally nonluminous, a phenomenon which is 

 known as fluorescence. 



Both of these properties find wide application in crime-detection 

 problems. Inasmuch as the fluorescent radiation is in general dif- 

 ferent in wave length or color from the incipient radiation and in 

 many instances is highly characteristic of the material illuminated. 



