STORING-UP OF " N" RAYS 39 



been extinguished and removed the phos- 

 phorescent glow, to my great surprise, remained 

 almost as strong as ever, but was darkened by 

 the interposition of lead, or wet paper, or the 

 hand, between the lantern and the sulphide. 

 Nothing was altered by the suppression of the 

 Auer burner, except that the observed actions 

 grew progressively weaker. At the end of 

 twenty minutes they still existed, but were 

 scarcely noticeable. 



Studying closely the circumstances of the 

 phenomenon, I was not long in recognizing that 

 the quartz lens had itself become a source of 

 " N " rays ; for when this was removed, all 

 action on the sulphide ceased, whereas if it was 

 brought nearer the sulphide, even laterally, the 

 latter would become more luminous. I then 

 took a quartz plate 1 5 mms. thick, whose surface 

 formed a square of 5-cm. sides, and exposed this 

 to the " N " rays emitted by an Auer burner 

 through two sheets of aluminium and some 

 black paper. It became as active as the lens ; 

 when brought nearer the sulphide, it seemed, 

 according to Bichat's expression, as if a veil 

 darkening it was being removed. A still more 



