218 ANNUAL REPOET SMITHSONIAN INSTITUTION, 19 3 9 



it therefore offers one method of analysis to determine the nature 

 of unknown materials received for examination. For instance, in 

 connection with the investigation of rape cases, it frequently becomes 

 necessary to examine clothing for the presence of seminal stains. 

 Advantage is taken of the fact that such stains fluoresce brilliantly 

 under the ultraviolet light, to localize certain areas which are then 

 subjected to specific tests for the stain in question. The time saved 

 by virtue of such a preliminary examination is immediately obvious. 



Again, drawing on the field of document examination, we find the 

 fluorescence of certain materials permitting their use as secret inks, 

 invisible when viewed by ordinary lighting but standing out vividly 

 in glowing contrast when subjected to ultraviolet illumination. Thus, 

 the ultraviolet affords a rapid and convenient method of examination 

 of documents or other evidence suspected of carrying a secret message. 

 A special case of this application of ultraviolet is found in the exami- 

 nation of evidence containing obliterated writing, that is, writing 

 which for some reason or other has been removed by physical or 

 chemical processes. In many such cases there remain imbedded in 

 the surface of the document, invisible to the eye, one or more con- 

 stituents of the original writing ink which when viewed under the 

 ultraviolet light reveal the fluorescent outline of the original. Plate 

 2, figure 1, is a photograph taken by the usual methods of a portion 

 of a page from an account book belonging to the subject of a case 

 under investigation by this Bureau. Evidence in the case indicated 

 that the subject had represented the bank account to be much larger 

 than it actually was. From a preliminary examination of the first 

 entry shown in plate 2, figure 1, it was apparent that a number had 

 been placed before the entry and then subsequently removed, although 

 it was not possible to tell definitely what the number had been. 

 Wlien placed under the ultraviolet light, however, a "4" was seen to 

 stand out in a faint fluorescent glow, before the original entry. This 

 "4" is clearly visible in illustration plate 2, figure 2. The evidence 

 made available through the use of ultraviolet light in this instance 

 was of material assistance in the subsequent prosecution and convic- 

 tion of the subject. 



In order to utilize the selective reflection and transmission charac- 

 teristics which several materials exhibit for the ultraviolet region, it 

 is necessary to employ the action of the ultraviolet light directly on 

 a photographic plate or other suitable recording medium. This 

 process is readily carried out, of course, by the utilization of quartz 

 optical systems and appropriate filters, resulting in incontrovertible 

 evidence in those instances where the materials involved are such as 

 to yield to this method of attack. Used to supplement each other, 

 the two ultraviolet techniques outlined above have proved so valuable 



