﻿Prof. 
  J. 
  Trowbridge 
  on 
  Positive 
  Rays. 
  697 
  

  

  as 
  possible, 
  but 
  more 
  numerous 
  and 
  more 
  varied 
  experiments 
  

   are 
  needed 
  before 
  it 
  will 
  be 
  possible 
  to 
  map 
  out 
  the 
  phenomena 
  

   with 
  exactness. 
  But 
  the 
  results 
  show 
  clearly 
  that 
  — 
  

  

  (1) 
  The 
  secondary 
  radiation 
  from 
  different 
  substances, 
  

   due 
  to 
  the 
  /3 
  and 
  y 
  rays 
  of 
  radium, 
  varies 
  in 
  quality, 
  those 
  

   of 
  lower 
  atomic 
  weight 
  returning 
  a 
  greater 
  proportion 
  of 
  less 
  

   penetrating 
  rays. 
  

  

  (2) 
  When 
  the 
  less 
  penetrating 
  portion 
  of 
  a 
  primary 
  beam 
  

   of 
  /3 
  rays 
  from 
  radium 
  is 
  sorted 
  out, 
  the 
  secondary 
  rays 
  also 
  

   become 
  more 
  penetrating. 
  

  

  (3) 
  In 
  view 
  of 
  these 
  considerations 
  the 
  ionization 
  current 
  

   due 
  to 
  secondary 
  radiation, 
  measured 
  in 
  a 
  chamber 
  of 
  the 
  

   ordinary 
  form, 
  does 
  not 
  give 
  a 
  simple 
  or 
  accurate 
  determination 
  

   of 
  the 
  nature 
  of 
  that 
  radiation. 
  

  

  LVI. 
  Positive 
  Rays. 
  By 
  John 
  Teowbridge*. 
  

  

  MY 
  intention 
  in 
  undertaking 
  this 
  investigation 
  was 
  to 
  

   endeavour 
  to 
  measure 
  the 
  group 
  velocity 
  of 
  the 
  

   positive 
  rays 
  by 
  producing 
  a 
  standing 
  wave 
  ; 
  or 
  a 
  stratum 
  of 
  

   maximum 
  collisions 
  in 
  an 
  exhausted 
  tube 
  in 
  the 
  space 
  between 
  

   the 
  anode 
  and 
  the 
  cathode. 
  In 
  the 
  case 
  of 
  an 
  oscillating 
  

   circuit, 
  if 
  we 
  call 
  \ 
  the 
  wave-length, 
  v 
  the 
  velocity 
  of 
  light, 
  

   t 
  the 
  time 
  of 
  a 
  half 
  oscillation, 
  s 
  the 
  distance 
  between 
  the 
  

   anode 
  and 
  the 
  cathode, 
  v 
  the 
  velocity 
  of 
  the 
  positive 
  rays, 
  

   we 
  have 
  

  

  X 
  = 
  vt, 
  (Eq. 
  1) 
  

  

  s 
  = 
  v% 
  (Eq. 
  2) 
  

  

  \ 
  , 
  vs 
  

  

  v 
  X 
  

  

  If, 
  by 
  tuning 
  a 
  circuit 
  containing 
  a 
  condenser, 
  self-induction 
  , 
  

   and 
  the 
  exhausted 
  tube, 
  the 
  stratum 
  of 
  maximum 
  collisions 
  

   could 
  be 
  formed 
  at 
  the 
  orifice 
  in 
  the 
  cathode, 
  it 
  was 
  thought 
  

   that 
  none 
  of 
  the 
  positive 
  rays 
  would 
  enter 
  the 
  canal 
  region 
  ; 
  

   if, 
  on 
  the 
  other 
  hand, 
  the 
  positive 
  rays 
  swung, 
  so 
  to 
  speak, 
  

   with 
  the 
  oscillations 
  of 
  the 
  circuit, 
  a 
  maximum 
  fluorescence 
  

   could 
  be 
  obtained 
  on 
  a 
  suitably 
  placed 
  willemite 
  screen. 
  

  

  The 
  circuit 
  was 
  arranged 
  as 
  follows 
  : 
  aleyden-jar 
  L, 
  fig. 
  1, 
  

   was 
  charged 
  by 
  a 
  storage 
  -battery 
  of 
  ten 
  thousand 
  cells, 
  

  

  * 
  Communicated 
  by 
  the 
  Author. 
  

  

  