﻿60 
  Dr. 
  M. 
  Wolfke 
  on 
  a 
  New 
  

  

  opening 
  as 
  to 
  have 
  its 
  aluminium 
  side 
  outwards. 
  Behind 
  

   these 
  foils 
  the 
  photographic 
  plate 
  is 
  placed. 
  

  

  Thus 
  on 
  one 
  half 
  of 
  the 
  opening 
  the 
  positive 
  rays 
  fall 
  

   upon 
  a 
  heavy-metal 
  surface, 
  and 
  on 
  the 
  other 
  half 
  upon 
  an 
  

   aluminium 
  surface. 
  The 
  characteristic 
  radiation 
  of 
  the 
  

   heavy 
  metal 
  being 
  more 
  intense 
  and 
  harder 
  than 
  that 
  of 
  

   aluminium, 
  it 
  reaches 
  the 
  photographic 
  plate 
  with 
  an 
  in- 
  

   tensity 
  not 
  perceptibly 
  diminished. 
  On 
  the 
  other 
  hand, 
  the 
  

   characteristic 
  radiation 
  of 
  aluminium 
  is 
  weak 
  and 
  soft 
  and 
  is 
  

   absorbed 
  to 
  a 
  large 
  extent 
  by 
  the 
  layer 
  of 
  heavy 
  metal 
  through 
  

   which 
  it 
  has 
  to 
  pass. 
  Therefore, 
  if 
  it 
  is 
  true 
  that 
  the 
  cha- 
  

   racteristic 
  radiation 
  of 
  the 
  heavy 
  metal 
  is 
  excited 
  by 
  positive 
  

   rays, 
  then 
  the 
  impression 
  produced 
  on 
  the 
  photographic 
  plate 
  

   must 
  be 
  stronger 
  beneath 
  that 
  half 
  of 
  the 
  opening 
  where 
  the 
  

   positive 
  rays 
  fall 
  upon 
  heavy 
  metal, 
  and 
  less 
  strong 
  beneath 
  

   the 
  other 
  half, 
  where 
  they 
  encounter 
  an 
  aluminium 
  foil. 
  

   The 
  higher 
  the 
  intensity 
  of 
  excitation 
  of 
  the 
  characteristic 
  

   rays, 
  the 
  more 
  pronounced 
  will 
  be 
  this 
  difference 
  in 
  the 
  

   strength 
  of 
  the 
  impression 
  obtained. 
  

  

  Such 
  secondary 
  cathode 
  raj's 
  as 
  might 
  have 
  been 
  produced 
  

   by 
  the 
  positive 
  rays 
  and 
  the 
  X-rays 
  in 
  the 
  channel 
  itself 
  were 
  

   deflected 
  behind 
  the 
  channel, 
  and 
  prevented 
  from 
  entering 
  

   the 
  opening 
  in 
  the 
  box 
  by 
  means 
  of 
  a 
  field 
  of 
  sufficient 
  power 
  

   created 
  between 
  channel 
  and 
  box. 
  

  

  In 
  order 
  to 
  eliminate 
  the 
  effect 
  that 
  might 
  have 
  been 
  pro- 
  

   duced 
  by 
  any 
  irregularity 
  of 
  thickness 
  in 
  the 
  two 
  foils, 
  every 
  

   test 
  made 
  was 
  checked 
  by 
  a 
  second 
  exposure 
  with 
  the 
  same 
  

   foils 
  as 
  in 
  the 
  first 
  case, 
  but 
  turned 
  about 
  so 
  as 
  to 
  have 
  their 
  

   relative 
  position 
  reversed. 
  

  

  In 
  order 
  to 
  avoid 
  too 
  strong 
  heating 
  of 
  the 
  foils 
  by 
  these 
  

   powerful 
  positive 
  rays, 
  the 
  exposures 
  were 
  intermittent 
  so 
  

   that 
  short 
  exposures 
  alternated 
  with 
  longer 
  breaks. 
  

  

  Two 
  heavy 
  metals, 
  tin 
  and 
  lead, 
  were 
  treated. 
  The 
  foils 
  

   used 
  were 
  *016 
  mm. 
  thick 
  in 
  the 
  case 
  of 
  tin 
  and 
  '028 
  mm. 
  in 
  

   the 
  case 
  of 
  lead 
  ; 
  the 
  thickness 
  of 
  the 
  aluminium 
  foil 
  was 
  

   •007 
  mm. 
  

  

  The 
  experiments 
  have 
  shown 
  that 
  ichen 
  acted 
  upon 
  hy 
  positive 
  

   rays, 
  either 
  of 
  these 
  metals 
  emitted 
  a 
  penetrating 
  radiation 
  of 
  

   fair 
  intensity 
  ivhich 
  is 
  probably 
  its 
  characteristic 
  radiation. 
  

  

  When 
  tin 
  was 
  tested, 
  all 
  photographs 
  without 
  exception 
  

   showed 
  a 
  very 
  marked 
  contrast 
  — 
  that 
  is, 
  where 
  the 
  positive 
  

   rays 
  fell 
  upon 
  the 
  tin 
  surface, 
  the 
  darkening 
  of 
  the 
  plate 
  was 
  

   strongly 
  pronounced, 
  while 
  the 
  other 
  half 
  of 
  the 
  circular 
  

   imprint 
  showed 
  but 
  a 
  faint 
  darkening. 
  The 
  photograph 
  

   obtained 
  is 
  seen 
  in 
  the 
  annexed 
  figure, 
  and 
  this 
  result 
  was 
  in 
  

   accordance 
  with 
  anticipation. 
  

  

  