﻿440 
  Trowbridge 
  — 
  Production 
  of 
  the 
  X-rays 
  

  

  dently 
  produced 
  by 
  the 
  qutcoming 
  of 
  gases 
  which 
  have 
  been 
  

   occluded 
  in 
  the 
  metallic 
  terminals 
  and 
  on 
  the 
  glass 
  walls 
  of 
  the 
  

   tube. 
  Dr. 
  Rollins 
  of 
  Boston 
  has 
  lately 
  described 
  in 
  the 
  Elec- 
  

   trical 
  Engineer 
  what 
  seems 
  to 
  me 
  a 
  crucial 
  experiment 
  in 
  this 
  

   connection. 
  Two 
  Rontgen-ray 
  tubes 
  of 
  the 
  ordinary 
  focus 
  

   plane 
  pattern 
  were 
  joined 
  together 
  by 
  a 
  cross 
  connection 
  which 
  

   was 
  at 
  right 
  angle 
  to 
  the 
  axes 
  of 
  the 
  tubes. 
  The 
  arrangement 
  

   thus 
  constituted 
  a 
  double 
  X-ray 
  tube. 
  This 
  was 
  exhausted 
  to 
  a 
  

   high 
  degree; 
  the 
  same 
  degree 
  of 
  rarefaction 
  was 
  present 
  in 
  

   both 
  tubes. 
  One 
  of 
  the 
  tubes 
  was 
  then 
  heated 
  until 
  a 
  differ- 
  

   ence 
  of 
  potential 
  competent 
  to 
  produce 
  a 
  spark 
  in 
  air 
  of 
  an 
  

   inch 
  excited 
  the 
  X-rays 
  with 
  great 
  brilliancy 
  ; 
  at 
  the 
  same 
  time 
  

   a 
  difference 
  of 
  potential 
  giving 
  a 
  spark 
  of 
  eight 
  inches 
  could 
  

   not 
  excite 
  these 
  rays 
  in 
  the 
  other 
  connecting 
  tube 
  ; 
  the 
  same 
  

   degree 
  of 
  vacuum, 
  so 
  to 
  speak, 
  existed 
  in 
  both 
  tubes. 
  The 
  

   phenomenon 
  of 
  the 
  occlusion 
  of 
  gases 
  seems 
  to 
  be 
  the 
  control- 
  

   ling 
  one 
  in 
  the 
  production 
  of 
  the 
  rays 
  and 
  not 
  the 
  degree 
  of 
  

   exhaustion. 
  With 
  the 
  steady 
  battery 
  current 
  one 
  can 
  watch 
  

   this 
  phenomenon 
  to 
  great 
  advantage. 
  When 
  the 
  tube 
  is 
  heated 
  

   to 
  a 
  certain 
  critical 
  temperature 
  a 
  blue 
  cloud 
  proceeds 
  from 
  one 
  

   anode 
  and 
  is 
  met 
  by 
  the 
  cathode 
  beam 
  from 
  the 
  cathode. 
  If 
  

   the 
  strength 
  of 
  the 
  current 
  is 
  then 
  gradually 
  increased 
  by 
  

   diminishing 
  the 
  resistance 
  in 
  the 
  circuit 
  this 
  blue 
  cloud 
  fills 
  

   the 
  entire 
  tube 
  and 
  the 
  anticathode 
  grows 
  white-hot 
  and 
  the 
  

   X-rays 
  cease 
  to 
  appear. 
  When 
  the 
  current 
  is 
  diminished 
  the 
  

   anticathode 
  sinks 
  to 
  a 
  cherry 
  red, 
  the 
  blue 
  cloud 
  contracts 
  and 
  

   sinks 
  into 
  the 
  anode 
  and 
  the 
  X-rays 
  come 
  out 
  with 
  great 
  bril- 
  

   liancy. 
  The 
  disappearance 
  of 
  the 
  blue 
  cloud 
  betokens 
  a 
  rise 
  

   of 
  resistance 
  in 
  the 
  tube 
  ; 
  for 
  the 
  glow 
  on 
  the 
  anticathode 
  

   grows 
  less 
  and 
  less, 
  and 
  presently 
  if 
  the 
  current 
  is 
  not 
  increased 
  

   the 
  tube 
  is 
  completely 
  extinguished 
  and 
  a 
  reheating 
  is 
  neces- 
  

  

  sai 
  T- 
  

  

  A 
  steady 
  battery 
  current 
  with 
  an 
  adjustable 
  liquid 
  resistance 
  

  

  is 
  indispensable, 
  I 
  believe, 
  if 
  we 
  wish 
  to 
  study 
  the 
  best 
  con- 
  

   ditions 
  for 
  producing 
  the 
  rays. 
  A 
  storage 
  battery 
  of 
  forty 
  

   thousand 
  volts 
  enables 
  me 
  to 
  try 
  a 
  wide 
  range 
  of 
  voltage 
  and 
  

   current 
  strength 
  ; 
  moreover 
  the 
  radiant 
  point 
  of 
  the 
  rays 
  is 
  less 
  

   likely 
  to 
  produce 
  ghosts. 
  The 
  tubes 
  glow 
  in 
  a 
  perfectly 
  steady 
  

   way 
  and 
  the 
  degree 
  of 
  excitation 
  of 
  the 
  rays 
  seems 
  to 
  be 
  under 
  

   perfect 
  control. 
  The 
  phenomenon 
  of 
  occlusion 
  in 
  an 
  X-ray 
  

   tube 
  having 
  such 
  an 
  important 
  bearing 
  on 
  the 
  subject 
  of 
  the 
  

   passage 
  of 
  gases 
  through 
  a 
  rarefied 
  space, 
  I 
  was 
  interested 
  to 
  

   trace 
  the 
  phenomenon 
  from 
  a 
  pressure 
  one 
  or 
  two 
  millimeters 
  

   up 
  to 
  the 
  X-ray 
  stage. 
  I 
  used 
  for 
  this 
  purpose 
  an 
  end-on 
  tube 
  

   of 
  a 
  peculiar 
  construction. 
  One 
  end 
  of 
  the 
  tube 
  was 
  blown 
  

   out 
  into 
  a 
  thin 
  bulb 
  through 
  which 
  the 
  X-rays 
  could 
  be 
  

   observed 
  ; 
  it 
  was 
  possible 
  to 
  heat 
  this 
  tube 
  strongly 
  so 
  as 
  to 
  

  

  