﻿Transformations 
  of 
  X-Rays. 
  Ill 
  

  

  of 
  a 
  similar 
  electroscope 
  E2 
  placed 
  in 
  the 
  path 
  o£ 
  the 
  secondary 
  

   beam 
  passing 
  down 
  the 
  tube 
  D 
  (R2 
  removed) 
  as 
  indicated 
  in 
  

   the 
  Plan 
  ; 
  the 
  size 
  of 
  the 
  aperture 
  in 
  the 
  wall 
  of 
  this 
  electro- 
  

   scope 
  beino- 
  3x2 
  cms. 
  

  

  It 
  was 
  found 
  that 
  by 
  carefully 
  shielding 
  the 
  electroscopes 
  

   El 
  and 
  Eg 
  from 
  draughts 
  and 
  sudden 
  changes 
  of 
  temperature 
  

   very 
  reliable 
  readings 
  could 
  be 
  obtained, 
  the 
  motion 
  of 
  the 
  

   gold-leaf 
  being 
  absolutely 
  dead-beat. 
  

  

  Preliminary 
  experiments 
  also 
  showed 
  that 
  with 
  a 
  given 
  

   radiator 
  R^ 
  in 
  position 
  (1(2 
  being 
  removedj 
  the 
  ratio 
  of 
  the 
  

   deflexions 
  in 
  E, 
  and 
  Eo 
  when 
  the 
  bulb 
  had 
  reached 
  a 
  steady 
  

   state 
  rarely 
  varied 
  by 
  more 
  than 
  1 
  per 
  cent, 
  during 
  a 
  series 
  

   of 
  readings. 
  

  

  The 
  ordinary 
  Wilson 
  type 
  of 
  electroscope 
  was 
  found 
  to 
  be 
  

   quite 
  unsuitable 
  as 
  a 
  means 
  of 
  measuring 
  the 
  tertiary 
  radia- 
  

   tion 
  ; 
  the 
  type 
  of 
  electroscope 
  described 
  by 
  R. 
  T. 
  Beatty 
  in 
  

   his 
  paper 
  on 
  '' 
  Secondary 
  Rontgen 
  Radiation 
  in 
  Air 
  " 
  * 
  was 
  

   finally 
  adopted. 
  Briefly 
  described, 
  this 
  consisted 
  of 
  a 
  brass 
  

   case 
  having 
  two 
  sliding 
  quadrants 
  insulated 
  from 
  the 
  case 
  and 
  

   charged 
  to 
  potentials 
  of 
  +240 
  and 
  —240 
  volts 
  respectively 
  ; 
  

   an 
  insulated 
  gold-leaf 
  hung 
  vertically 
  between 
  them 
  and 
  was 
  

   connected 
  to 
  the 
  wire 
  e, 
  which 
  projected 
  into 
  and 
  was 
  

   insulated 
  from 
  the 
  ionization-chamber 
  I, 
  which 
  itself 
  was 
  

   insulated 
  and 
  charged 
  to 
  + 
  240 
  volts. 
  An 
  adjustable 
  com- 
  

   pensating 
  -chamber 
  insulated 
  and 
  charged 
  to 
  —240 
  volts 
  

   eliminated 
  the 
  normal 
  ionization 
  in 
  the 
  chamber 
  I. 
  The 
  

   sensitiveness 
  of 
  the 
  electroscope 
  was 
  adjustable 
  by 
  means 
  of 
  

   the 
  sliding 
  quadrants. 
  

  

  With 
  the 
  order 
  of 
  sensitiveness 
  required 
  in 
  all 
  the 
  experi- 
  

   ments 
  described, 
  the 
  motion 
  of 
  the 
  gold-leaf 
  was 
  dead-beat, 
  

   and 
  a 
  series 
  of 
  readings 
  of 
  the 
  ratio 
  of 
  deflexions 
  in 
  electro- 
  

   scopes 
  El 
  and 
  Eg 
  showed 
  that 
  with 
  deflexions 
  up 
  to 
  20 
  scale- 
  

   divisions 
  in 
  E2 
  this 
  could 
  be 
  obtained 
  with 
  an 
  accuracy 
  of 
  

   2 
  per 
  cent, 
  with 
  certainty. 
  

  

  A 
  calibration 
  of 
  electroscopes 
  Ei 
  and 
  Eg 
  showed 
  that 
  the 
  

   value 
  of 
  a 
  deflexion 
  of 
  a 
  scale-division 
  was 
  the 
  same 
  within 
  

   1 
  per 
  cent, 
  throughout 
  the 
  range 
  of 
  scale 
  employed. 
  

  

  The 
  sensitiveness 
  of 
  Eg 
  was 
  adjusted 
  and 
  then 
  maintained 
  

   constant 
  throughout 
  a 
  given 
  series 
  of 
  readings, 
  and 
  in 
  all 
  

   readings 
  a 
  constant 
  deflexion 
  of 
  E3 
  was 
  used, 
  thus 
  eliminating 
  

   the 
  effect 
  of 
  the 
  slight 
  change 
  in 
  value 
  of 
  a 
  scale-division 
  

   which 
  was 
  found 
  to 
  exist 
  in 
  different 
  parts 
  of 
  the 
  scale. 
  

  

  Preliminary 
  experiments 
  showed 
  that 
  the 
  secondary 
  radia- 
  

   tion 
  from 
  air 
  together 
  with 
  other 
  stray 
  eff'ects 
  were 
  very 
  

  

  * 
  R. 
  T. 
  Beatty, 
  Phil. 
  Mag-. 
  Nov. 
  1907, 
  pp. 
  604-614. 
  

  

  