﻿Hig) 
  h- 
  Frequency 
  Spectra 
  in 
  Geissler 
  Tubes. 
  967 
  

  

  Descriptive. 
  

  

  During 
  the 
  earlier 
  stages 
  of 
  the 
  work, 
  ordinary 
  glass 
  

   discharge 
  tubes 
  were 
  used, 
  with 
  electrodes 
  of 
  platinum 
  and 
  

   aluminium. 
  It 
  was 
  found, 
  however, 
  that 
  enormous 
  heating 
  

   took 
  place 
  in 
  these 
  discharge 
  tubes, 
  and 
  after 
  only 
  a 
  few 
  

   seconds' 
  action 
  they 
  collapsed, 
  owing 
  to 
  softening 
  of 
  the 
  glass 
  

   or 
  uneven 
  expansion 
  at 
  the 
  electrodes. 
  Geissler 
  tubes 
  of 
  the 
  

   usual 
  pattern, 
  but 
  with 
  external 
  electrodes, 
  were 
  then 
  tried. 
  

   Three 
  forms 
  of 
  external 
  electrode 
  were 
  tested, 
  and 
  one 
  

   consisting 
  of 
  small 
  cups 
  of 
  mercury 
  round 
  the 
  bulbs 
  was 
  

   eventually 
  decided 
  on. 
  The 
  current 
  was 
  led 
  to 
  the 
  tube 
  by 
  

   means 
  of 
  a 
  platinum-tipped 
  wire 
  dipping 
  into 
  one 
  of 
  these 
  

   cups, 
  and 
  the 
  exit 
  wire 
  dipped 
  into 
  that 
  round 
  the 
  other 
  bulb. 
  

   This 
  type 
  of 
  external 
  electrode 
  does 
  not 
  appear 
  to 
  have 
  been 
  

   used 
  hitherto, 
  and 
  can 
  be 
  specially 
  recommended 
  as 
  being- 
  

   more 
  generally 
  useful 
  than 
  the 
  ordinary 
  forms, 
  viz.: 
  (a) 
  Tin- 
  

   foil 
  wrappings 
  round 
  the 
  bulbs, 
  (b) 
  Cylindrical 
  brass 
  cups 
  

   round 
  the 
  bulbs, 
  the 
  intervening 
  space 
  being 
  tightly 
  packed 
  

   with 
  powdered 
  graphite. 
  The 
  danger 
  of 
  piercing 
  the 
  tube 
  

   owing 
  to 
  imperfect 
  contact 
  of 
  electrode 
  and 
  glass 
  was 
  found 
  

   to 
  be 
  greatly 
  reduced 
  by 
  use 
  of 
  these 
  external 
  mercury 
  

   cups. 
  But 
  even 
  with 
  these 
  cups 
  surrounding 
  the 
  glass 
  bulbs, 
  

   the 
  tubes 
  were 
  still 
  liable 
  to 
  collapse, 
  owing 
  to 
  the 
  great 
  

   heating 
  produced 
  by 
  the 
  present 
  type 
  of 
  discharge. 
  Where 
  

   the 
  glass 
  was 
  slightly 
  thinner 
  than 
  in 
  the 
  surrounding 
  parts, 
  

   the 
  current 
  appeared 
  to 
  pass 
  more 
  readily, 
  and 
  the 
  consequent 
  

   rapid 
  local 
  heating 
  very 
  soon 
  resulted 
  in 
  holes 
  being 
  blown 
  

   through 
  the 
  bulbs. 
  After 
  much 
  preliminary 
  work 
  on 
  various 
  

   tubes, 
  it 
  was 
  ultimately 
  decided 
  to 
  use 
  tubes 
  of 
  fused 
  silica*. 
  

   These 
  were 
  of 
  the 
  pattern 
  shown 
  in 
  fig. 
  1. 
  Connexion 
  was 
  

  

  Fig. 
  1. 
  

  

  S»MCA 
  

  

  MERCVB.Y 
  

   ASBESTOS 
  COLLAR. 
  

  

  To 
  PVMP 
  

  

  SCALING 
  WAX 
  

   OOINT 
  

  

  made 
  with 
  the 
  rest 
  of 
  the 
  glass 
  apparatus 
  by 
  means 
  of 
  a 
  

   sealing-wax 
  joint, 
  mercury-sealed 
  as 
  shown 
  in 
  figure. 
  The 
  

   electrodes 
  were 
  of 
  the 
  external 
  mercury 
  form, 
  and 
  consisted 
  

  

  * 
  As 
  obtainable 
  from 
  the 
  Silica 
  Syndicate, 
  Hatton 
  Garden, 
  London. 
  

  

  