﻿Rotation 
  of 
  Electric 
  Discharge. 
  549 
  

  

  am 
  also 
  engaged 
  in 
  working 
  out 
  a 
  theory 
  of 
  these 
  rotations. 
  

   In 
  the 
  meantime, 
  the 
  following 
  conclusions 
  are 
  justified 
  by 
  the 
  

   results 
  already 
  obtained. 
  

  

  Conclusions. 
  

  

  1. 
  The 
  discharge 
  in 
  a 
  De 
  La 
  Rive's 
  tube, 
  in 
  general, 
  passes 
  

   through 
  three 
  stages, 
  " 
  showery/' 
  " 
  band," 
  and 
  " 
  glow.-" 
  

  

  In 
  air, 
  when 
  the 
  distance 
  between 
  the 
  electrodes 
  is 
  small, 
  

   the 
  first 
  stage 
  is 
  absent. 
  

  

  2. 
  The 
  discharge 
  rotates 
  under 
  the 
  influence 
  of 
  the 
  mag- 
  

   netic 
  field, 
  only 
  when 
  it 
  is 
  in 
  the 
  form 
  of 
  a 
  "band/' 
  over 
  

   a 
  range 
  of 
  pressure, 
  depending 
  on 
  the 
  nature 
  of 
  the 
  gas 
  or 
  

   vapour 
  in 
  the 
  tube, 
  the 
  E.M.F. 
  producing 
  the 
  discharge, 
  and 
  

   the 
  distance 
  between 
  the 
  electrodes. 
  

  

  3. 
  Gases 
  can 
  be 
  divided 
  into 
  two 
  groups 
  as 
  regards 
  the 
  law 
  

   of 
  rotation 
  : 
  

  

  (1) 
  In 
  gases 
  such 
  as 
  Air, 
  H 
  *, 
  N 
  *, 
  jST 
  2 
  0, 
  i. 
  e., 
  probably 
  all 
  

   elementary 
  gases 
  and 
  those 
  which 
  do 
  not 
  decompose 
  

   under 
  the 
  electric 
  discharge, 
  for 
  a 
  certain 
  range 
  of 
  

   pressure 
  (depending 
  on 
  the 
  distance 
  between 
  the 
  elec- 
  

   trodes 
  and 
  E.M.F. 
  producing 
  the 
  discharge) 
  

  

  t 
  = 
  constant, 
  which 
  varies 
  inversely 
  as 
  the 
  density 
  of 
  the 
  

  

  gas, 
  where 
  T 
  is 
  the 
  period 
  of 
  rotation 
  at 
  pressure 
  p. 
  For 
  

  

  lower 
  pressures, 
  {p 
  decreases 
  as 
  pressure 
  decreases. 
  

  

  (2) 
  In 
  other 
  gases 
  (e. 
  g., 
  C0 
  2 
  , 
  S0 
  2 
  ), 
  which 
  probably 
  

   tend 
  to 
  decompose 
  when 
  the 
  discharge 
  passes 
  through 
  

  

  them, 
  and 
  probably 
  all 
  vapours 
  (e. 
  </., 
  C 
  CI4), 
  £ 
  increases 
  

  

  with 
  pressure 
  and 
  with 
  the 
  density 
  of 
  the 
  gas 
  (fig. 
  13). 
  

  

  4. 
  In 
  the 
  case 
  of 
  the 
  first 
  group 
  of 
  gases, 
  for 
  pressures 
  at 
  

  

  which 
  there 
  is 
  rotation 
  according 
  to 
  the 
  law 
  7^ 
  = 
  constant, 
  

  

  the 
  potential-difference 
  between 
  the 
  electrodes 
  is 
  a 
  linear 
  

   function 
  of 
  the 
  pressure. 
  

  

  For 
  each 
  group 
  the 
  potential-difference 
  between 
  the 
  elec- 
  

   trode 
  increases 
  with 
  the 
  density 
  of 
  the 
  gas. 
  

  

  * 
  Prof. 
  H. 
  A. 
  "Wilson 
  and 
  Mr. 
  Martyn 
  have 
  investigated 
  the 
  law 
  

   relating; 
  to 
  these 
  gases. 
  

  

  