Phil.  Mag.  Ser.  6,  Vol.  11,  PL  IT. 
Fig.  1. 
-*■  8  layers  of  foil. 
-*■  bare. 
Magnification  1*4. 
Fig.  2. 
Magnification  1*4. 
Fig.  3. 
->-  air  bands. 
-*•  vacuum  bands. 
Magnification  1*4. 
