﻿GrIBSOX, 
  

  

  Phil.Mag.Ser. 
  6, 
  Vol. 
  26, 
  PL 
  XX. 
  

  

  Fig. 
  1. 
  — 
  Tube 
  diameter 
  -78 
  

  

  llli'' 
  

  

  Fig. 
  2.— 
  Tube 
  diameter 
  1-680 
  cm. 
  

  

  Fig. 
  3.— 
  Tube 
  diameter 
  2'G95 
  cm. 
  

  

  