?ELL.— Opacity or Certain Glasses. 



Plate II. 



=> 1 » 



|.^^|^>4*''»>4^f M« M -^^fll^ 



Bare tube. 

 r> minutes 



Bare tube. 

 5 seconds. 



" Abiotic " radiations. 



Proc. Amer. Acad. Arts and Sciences. Vol. XLVI. 



