FIG. 6. 



,, XT With " N " rays proceeding 



Without N rays. from & Ner nst lamp. 



FJG. 7. 



Without " N " rays. 



With " N " rays produced 

 by two large files. 



[To face p. 66. 



N.B. The strise and most of the spots in the figures do not exist in the 

 original photograph, but are the result of the inability of the 

 photogravure process to reproduce images of this kind. 



