﻿532 
  Prof. 
  D. 
  X. 
  Mallik 
  on 
  Magnetic 
  

  

  the 
  distance 
  between 
  the 
  electrodes 
  and 
  the 
  nature 
  o£ 
  the 
  

   gas, 
  the 
  discharge 
  passes, 
  but 
  this 
  discharge 
  when 
  it 
  becomes 
  

   continuous 
  is, 
  as 
  a 
  rule 
  (§ 
  18), 
  in 
  the 
  form 
  of 
  a 
  spray 
  or 
  

   shower 
  consisting 
  of 
  infinite 
  number 
  of 
  streams 
  or 
  " 
  rays 
  " 
  

   all 
  round 
  the 
  axis 
  of 
  the 
  tube. 
  This 
  discharge 
  is 
  unaffected 
  

   when 
  the 
  electromagnet 
  is 
  excited. 
  

  

  Figs. 
  2, 
  3 
  (PI. 
  XXL) 
  are 
  photographs 
  * 
  of 
  such 
  a 
  discharge 
  

   in 
  air. 
  The 
  streams 
  seem 
  to 
  be 
  reflected 
  at 
  the 
  side 
  of 
  the 
  

   vessel 
  ; 
  their 
  shape 
  therefore 
  depends 
  partly 
  at 
  least 
  on 
  

   the 
  shape 
  and 
  dimensions 
  of 
  the 
  vessel 
  and 
  the 
  electrodes. 
  

   Fig. 
  3 
  shows 
  also 
  a 
  few 
  bright 
  streaks. 
  They 
  were 
  formed 
  

   temporarily, 
  one 
  after 
  the 
  other, 
  during 
  exposure 
  of 
  the 
  plate, 
  

   and 
  were 
  the 
  results 
  of 
  the 
  confluence 
  of 
  a 
  certain 
  number 
  of 
  

   " 
  streams." 
  

  

  3. 
  As 
  the 
  exhaustion 
  proceeds, 
  more 
  and 
  more 
  of 
  the 
  rays 
  

   aggregate 
  into 
  a 
  band 
  which 
  becomes 
  brighter 
  and 
  thicker 
  

   as 
  aggregation 
  proceeds. 
  This 
  band 
  is 
  at 
  first 
  unsteady 
  

   owing 
  evidently 
  to 
  the 
  fact 
  that 
  there 
  is 
  a 
  continuous 
  change 
  

   in 
  the 
  constituent 
  streams. 
  Fig. 
  3 
  shows 
  the 
  initial 
  stage 
  of 
  

   this 
  process. 
  

  

  4. 
  The 
  bright 
  band 
  gradually 
  becomes 
  steady 
  when 
  the 
  

   constituents 
  do 
  not 
  any 
  longer 
  change 
  with 
  time. 
  It 
  then 
  

   extends 
  from 
  a 
  definite 
  point 
  on 
  the 
  ring 
  to 
  the 
  nearest 
  

   point 
  of 
  the 
  disk 
  (cathode), 
  which 
  is 
  partially 
  surrounded 
  

   by 
  a 
  glow. 
  

  

  In 
  the 
  present 
  apparatus 
  (in 
  which 
  the 
  ring 
  has 
  a 
  gap) 
  

   this 
  point 
  in 
  the 
  ring 
  is 
  about 
  180° 
  from 
  this 
  gap. 
  It 
  is 
  

   apparently 
  the 
  point 
  in 
  the 
  ring 
  at 
  which 
  the 
  electric 
  density 
  

   is 
  greatest, 
  and 
  the 
  path 
  of 
  the 
  band 
  then 
  meets 
  the 
  anode 
  

   at 
  the 
  point 
  at 
  which 
  normal 
  electric 
  force 
  is 
  greatest. 
  

  

  Fig. 
  4 
  (PL 
  XXL) 
  shows 
  a 
  fully 
  developed 
  " 
  band 
  " 
  dis 
  

   charge. 
  [The 
  dark 
  space 
  in 
  this 
  is 
  only 
  apparent 
  by 
  

   contrast.] 
  

  

  5. 
  The 
  pressure 
  at 
  which 
  this 
  band 
  attains 
  steadiness 
  ar.d 
  

   definite 
  form 
  depends 
  on 
  the 
  E.M.F. 
  of 
  the 
  induction-coil 
  

   and 
  also 
  on 
  the 
  distance 
  between 
  the 
  electrodes 
  and 
  the 
  

   nature 
  of 
  the 
  gas. 
  

  

  With 
  the 
  induction-coil 
  I 
  have 
  used 
  in 
  these 
  experiments, 
  

   and 
  for 
  air, 
  when 
  there 
  were 
  three 
  cells 
  in 
  the 
  primary 
  

   circuit, 
  this 
  state 
  was 
  attained 
  somewhere 
  about 
  the 
  pressure 
  

   of 
  22 
  millimetres 
  of 
  mercury. 
  With 
  four 
  cells 
  it 
  was 
  about 
  

   2Q 
  millimetres, 
  and 
  with 
  five 
  cells 
  about 
  30 
  millimetres, 
  the 
  

   distance 
  between 
  the 
  electrodes 
  being 
  18 
  cm. 
  

  

  6. 
  It 
  is 
  when 
  the 
  discharge 
  forms 
  a 
  band 
  of 
  definite 
  shape 
  

   that 
  rotation 
  ensues 
  on 
  the 
  application 
  of 
  the 
  magnetic 
  field. 
  

  

  * 
  Kindly 
  taken 
  for 
  me 
  by 
  Mr. 
  Hughes 
  of 
  the 
  Cavendish 
  Laboratory. 
  

  

  