﻿550 
  Dr. 
  C. 
  G. 
  Barkla 
  and 
  Mr. 
  C. 
  A. 
  Sadler 
  on 
  

  

  5. 
  For 
  all 
  substances, 
  the 
  potential- 
  difference 
  increases 
  with 
  

   pressure 
  (except 
  for 
  very 
  low 
  pressures), 
  with 
  the 
  E.M.F. 
  

   producing 
  the 
  discharge, 
  and 
  the 
  distance 
  between 
  the 
  

   electrodes. 
  

  

  6. 
  In 
  air, 
  and 
  probably 
  in 
  all 
  gases, 
  the 
  angular 
  velocity 
  

   of 
  rotation 
  is 
  proportional 
  to 
  the 
  E.M.F. 
  producing 
  the 
  

   discharge, 
  and 
  increases 
  as 
  the 
  spark-length 
  decreases. 
  

  

  , 
  «. 
  « 
  KAS 
  

  

  /. 
  feince 
  — 
  gc 
  r 
  9 
  7 
  ' 
  

  

  m 
  yds 
  

  

  1 
  

  

  x 
  

  

  K^KjS 
  ; 
  

  

  but 
  since 
  S 
  increases 
  with 
  density 
  and 
  T 
  also 
  increases 
  with 
  

   density, 
  K^K 
  2 
  rapidly 
  decreases 
  as 
  density 
  increases. 
  

  

  8. 
  KjKo 
  is 
  independent 
  of 
  the 
  distance 
  between 
  the 
  elec- 
  

   trodes 
  (except 
  in 
  so 
  far 
  as 
  the 
  potential-difference 
  in 
  the 
  

   discharge 
  depends 
  on 
  it) 
  but 
  varies 
  with 
  the 
  E.M.F. 
  of 
  

   the 
  discharge. 
  

  

  I 
  have 
  to 
  thank 
  Professor 
  J. 
  J. 
  Thomson 
  for 
  permission 
  

   to 
  work 
  at 
  the 
  Cavendish 
  Laboratory 
  and 
  for 
  many 
  valuable 
  

   suggestions. 
  

  

  XL 
  VTII. 
  Homogeneous 
  Secondary 
  Rontgen 
  Radiations. 
  By 
  

   Charles 
  G. 
  Barkla, 
  M.A., 
  JJ.Sc, 
  Lecturer 
  in 
  Advanced 
  

   Electricity, 
  and 
  Charles 
  A. 
  Sadler, 
  M.Sc, 
  Demonstrator 
  

   in 
  Physics, 
  University 
  of 
  Liverpool* 
  . 
  

  

  THOUGH 
  there 
  are 
  many 
  phenomena 
  of 
  Secondary 
  

   Rontgen 
  Rays 
  still 
  awaiting 
  investigation, 
  it 
  seems 
  

   desirable 
  in 
  publishing 
  the 
  results 
  of 
  recent 
  experiments 
  — 
  

   principally 
  on 
  the 
  homogeneous 
  secondary 
  radiations 
  — 
  that 
  

   a 
  general 
  survey 
  should 
  be 
  made 
  of 
  the 
  whole 
  subject 
  of 
  

   " 
  Secondary 
  X-Rays 
  emitted 
  by 
  substances 
  subject 
  to 
  

   X-Rays/' 
  and 
  that 
  a 
  more 
  concise 
  statement 
  of 
  the 
  experi- 
  

   mental 
  results 
  and 
  the 
  conclusions 
  based 
  on 
  these 
  should 
  

   be 
  given. 
  This, 
  indeed, 
  appears 
  a 
  necessity 
  not 
  only 
  in 
  

   order 
  to 
  make 
  intelligible 
  the 
  results 
  of 
  what 
  would 
  other- 
  

   wise 
  appear 
  isolated 
  experiments 
  of 
  little 
  significance, 
  but 
  to 
  

   exhibit 
  the 
  observed 
  limitations 
  or 
  the 
  generality 
  of 
  laws 
  

  

  * 
  Communicated 
  by 
  the 
  Physical 
  Society 
  : 
  read 
  June 
  12, 
  1908. 
  

   The 
  expenses 
  of 
  this 
  research 
  have 
  been 
  partially 
  covered 
  by 
  a 
  

   Government 
  Grant 
  through 
  the 
  Royal 
  Society.— 
  C. 
  G. 
  B. 
  

  

  