﻿162 
  

  

  Dr. 
  J. 
  Kunz 
  on 
  Cathode 
  and 
  

  

  Experiment 
  1. 
  — 
  The 
  vacuum 
  was 
  made 
  by 
  means 
  of 
  a 
  

   mercury-pump 
  in 
  a 
  bulb 
  of 
  the 
  form 
  shown 
  in 
  fig. 
  1. 
  The 
  

   cathode 
  is 
  a 
  cylindrical 
  tube 
  of 
  brass, 
  2*4 
  cm. 
  long, 
  0*4 
  cm. 
  

   in 
  diameter. 
  

  

  Fig. 
  1. 
  

  

  The 
  anode 
  is 
  a 
  ring 
  of 
  

   aluminium. 
  The 
  wires 
  in 
  the 
  tube 
  are 
  

   insulated 
  from 
  one 
  another 
  by 
  glass 
  tubes, 
  

   and 
  the 
  bulb 
  is 
  sealed 
  up 
  with 
  ebonite 
  

   and 
  sealing-wax. 
  If 
  now 
  the 
  air 
  is 
  

   gradually 
  pumped 
  out, 
  at 
  a 
  certain 
  stage 
  

   the 
  cathode 
  is 
  found 
  to 
  be 
  surrounded 
  

   by 
  a 
  comparatively 
  dark 
  space, 
  called 
  

   Crookes's. 
  Beyond 
  this 
  dark 
  space 
  and 
  

   enveloping 
  it, 
  there 
  is 
  a 
  very 
  bright 
  

   luminous 
  ring, 
  called 
  the 
  negative 
  glow. 
  

   This 
  ring 
  passes 
  through 
  the 
  hole 
  of 
  the 
  

   cathode 
  and 
  emits 
  a 
  very 
  vivid 
  violet 
  

   light 
  Beyond 
  the 
  luminous 
  region 
  there 
  

   is 
  another 
  comparatively 
  dark 
  space 
  — 
  

   Faraday's 
  dark 
  space 
  — 
  of 
  a 
  very 
  variable 
  

   length 
  even 
  at 
  constant 
  pressure. 
  Be- 
  

   tween 
  this 
  dark 
  space 
  and 
  the 
  anode 
  

   there 
  is 
  a 
  luminous 
  column, 
  called 
  the 
  

   positive 
  column, 
  which, 
  when 
  the 
  current 
  and 
  pressure 
  

   are 
  within 
  certain 
  limits, 
  exhibits 
  the 
  well-known 
  alternations 
  

   of 
  dark 
  and 
  bright 
  spaces 
  — 
  the 
  striations. 
  If 
  now 
  the 
  

   pressure 
  is 
  diminished, 
  a 
  thin 
  layer 
  of 
  yellow 
  luminosity 
  

  

  \ 
  

  

  begins 
  to 
  spread 
  all 
  over 
  the 
  inner 
  and 
  outer 
  surface 
  of 
  the 
  

   negative 
  electrode, 
  the 
  negative 
  dark 
  space 
  gets 
  bigger, 
  the 
  

  

  light 
  in 
  the 
  hole 
  of 
  the 
  cathode 
  be 
  

  

  .,.- 
  -sger, 
  the 
  

   eonies 
  more 
  intense 
  : 
  it 
  is 
  

  

  