﻿TTansformations 
  of 
  X- 
  Rays. 
  117 
  

  

  were 
  obtained. 
  Let 
  the 
  value 
  of 
  the 
  ratio 
  o£ 
  the 
  deflexions 
  

   of 
  the 
  gold-leaves 
  in 
  E3 
  and 
  Ei 
  be 
  rg, 
  and 
  when 
  the 
  tertiary 
  

   radiator 
  was 
  removed 
  and 
  the 
  air 
  alone 
  in 
  its 
  neighbourhood 
  

   acted 
  as 
  a 
  source 
  o£ 
  tertiary 
  rays, 
  let 
  the 
  corresponding 
  value 
  

   of 
  the 
  ratio 
  be 
  ^2'. 
  

  

  The 
  tertiary 
  radiator 
  Hg 
  was 
  then 
  replaced 
  and 
  the 
  ratio 
  rg 
  

   again 
  found, 
  and 
  then 
  finally 
  removing 
  E.2 
  the 
  readings 
  for 
  

   the 
  ratio 
  ?'i 
  were 
  repeated. 
  

  

  Working 
  with 
  an 
  X-ray 
  bulb, 
  having 
  an 
  auxiliary 
  spark- 
  

   gap, 
  it 
  was 
  found 
  that 
  in 
  the 
  steady 
  state 
  the 
  two 
  sets 
  of 
  

   values 
  for 
  Vi 
  and 
  likewise 
  those 
  for 
  ?'2 
  showed 
  agreement 
  to 
  

   within 
  2 
  per 
  cent. 
  

  

  In 
  no 
  case 
  was 
  the 
  air-effect 
  r/ 
  more 
  than 
  1 
  per 
  cent, 
  of 
  

   the 
  value 
  of 
  ri, 
  in 
  most 
  cases 
  less 
  than 
  \ 
  oi 
  1 
  per 
  cent.; 
  and 
  

   in 
  no 
  case 
  was 
  the 
  air-eftect 
  r^ 
  more 
  than 
  2 
  per 
  cent, 
  of 
  the 
  

   value 
  of 
  ?'2 
  when 
  the 
  characteristic 
  homogeneous 
  radiation 
  

   was 
  excited. 
  

  

  In 
  those 
  cases 
  where 
  the 
  penetrating 
  power 
  of 
  the 
  secondary 
  

   beam 
  did 
  not 
  exceed 
  that 
  of 
  the 
  characteristic 
  radiation 
  from 
  

   the 
  tertiary 
  radiator 
  employed, 
  the 
  air-effect 
  r^ 
  became 
  of 
  

   considerable 
  importance, 
  being 
  as 
  high 
  as 
  ^ 
  of 
  ^2 
  in 
  some 
  

   cases. 
  The 
  author 
  hopes 
  to 
  obtain 
  more 
  reliable 
  data 
  in 
  

   these 
  particular 
  cases 
  in 
  the 
  course 
  of 
  further 
  experiments. 
  

  

  It 
  will 
  be 
  seen 
  later, 
  however, 
  that 
  an 
  accurate 
  knowledge 
  

   of 
  these 
  particular 
  data 
  is 
  not 
  essential 
  in 
  the 
  present 
  investi- 
  

   gation. 
  

  

  It 
  was 
  estimated 
  that 
  if 
  in 
  all 
  other 
  cases 
  ^ 
  of 
  the 
  air- 
  

   effect 
  was 
  taken 
  in 
  addition 
  to 
  the 
  normal 
  leakage, 
  and 
  this 
  

   subtracted 
  in 
  each 
  case 
  from 
  the 
  direct 
  effect 
  when 
  the 
  

   metallic 
  radiator 
  was 
  in 
  position, 
  the 
  resulting 
  ratios 
  finally 
  

   obtained 
  would 
  be 
  accurate 
  to 
  at 
  least 
  2 
  per 
  cent. 
  If 
  a 
  denote 
  

   the 
  ratio 
  of 
  the 
  normal 
  leakage 
  in 
  any 
  given 
  time 
  in 
  the 
  

   electroscope 
  E2 
  to 
  the 
  deflexion 
  in 
  E^ 
  in 
  the 
  same 
  time, 
  with 
  a 
  

   primary 
  beam 
  as 
  during 
  the 
  actual 
  experiment, 
  then 
  since 
  

   the 
  normal 
  leakage 
  is 
  compensated 
  for 
  in 
  E3, 
  the 
  ratio 
  of 
  the 
  

   ionizations 
  in 
  the 
  electroscopes 
  E3 
  and 
  Eg 
  due 
  to 
  the 
  homo- 
  

   geneous 
  radiations 
  

  

  2 
  2 
  '2 
  

  

  •\, 
  ^'^ 
  , 
  = 
  R 
  (say), 
  

  

  If 
  the 
  absorption 
  coefficient 
  of 
  the 
  homogeneous 
  radiation 
  

   from 
  a 
  given 
  tertiary 
  radiator 
  by 
  Al 
  be 
  denoted 
  by 
  \c,, 
  and 
  

   that 
  of 
  the 
  exciting 
  secondary 
  radiation 
  by 
  Xj, 
  then 
  as 
  long 
  

   as 
  X-i 
  = 
  or 
  is 
  > 
  X2 
  the 
  value 
  of 
  R 
  is 
  quite 
  small 
  and 
  approxi- 
  

   mately 
  constant. 
  As 
  Xi 
  decreases 
  through 
  the 
  value 
  Xg 
  wo 
  

   get 
  a 
  ra})id 
  increase 
  in 
  the 
  value 
  of 
  li, 
  and 
  for 
  a 
  comparatively 
  

  

  