﻿TWENTIETH 
  CENTUEY 
  PHYSICS 
  MILLIKAN 
  197 
  

  

  everywhere 
  been 
  verified, 
  but 
  it 
  is 
  one 
  which 
  is 
  to 
  the 
  present 
  day 
  

   comi:>letely 
  inexplicable 
  in 
  terms 
  of 
  the 
  nineteenth 
  century 
  wave 
  

   theory. 
  It 
  obviousiy 
  fits 
  better 
  some 
  sort 
  of 
  corpuscular 
  theory 
  than 
  

   a 
  wave 
  theory. 
  It 
  is 
  a 
  new 
  phenomenon 
  of 
  stupendous 
  importance 
  

   for 
  the 
  understanding 
  of 
  the 
  foundations 
  of 
  the 
  physical 
  world 
  in 
  

   which 
  we 
  live. 
  

  

  Sixth. 
  But 
  now 
  came, 
  about 
  1913, 
  the 
  discovery 
  of 
  the 
  effect 
  

   inverse 
  to 
  the 
  last. 
  Not 
  only 
  was 
  the 
  energy 
  communicated 
  to 
  an 
  

   electron 
  by 
  an 
  ether 
  wave 
  which 
  was 
  absorbed 
  by 
  that 
  electron, 
  

   proportional 
  to 
  the 
  frequency 
  of 
  the 
  wave, 
  but 
  when 
  atoms 
  of 
  sub- 
  

   stances 
  like 
  glowing 
  hydrogen, 
  for 
  example, 
  emit 
  ether 
  waves, 
  the 
  

   frequency 
  of 
  the 
  emitted 
  light 
  can 
  be 
  found 
  by 
  considering 
  the 
  

   electron 
  in 
  the 
  act 
  of 
  emission 
  to 
  have 
  fallen 
  from 
  one 
  energy 
  level 
  

   A\, 
  to 
  a 
  second 
  E., 
  and 
  to 
  have 
  emitted 
  a 
  frequency 
  proportional 
  to 
  

   the 
  change 
  in 
  energy, 
  i. 
  e., 
  to 
  E^ 
  — 
  En, 
  the 
  factor 
  of 
  proportionality 
  

   being 
  the 
  same 
  universal 
  constant 
  A; 
  so 
  that 
  the 
  equation 
  A\=^i&'2~'^<'»' 
  

   gives 
  a 
  reciprocal 
  relation 
  between 
  the 
  electronic 
  energy 
  and 
  ether 
  

   wave 
  energy. 
  This 
  experimental 
  discovery, 
  first, 
  that 
  the 
  frequency 
  

   of 
  an 
  ether 
  wave 
  may 
  be 
  taken 
  as 
  a 
  measure 
  of 
  its 
  energy 
  available 
  

   for 
  absorption 
  by 
  electrons, 
  and 
  second, 
  that 
  the 
  energy 
  hv 
  can 
  

   interplay 
  in 
  this 
  way 
  between 
  ether 
  waves 
  and 
  electrons 
  in 
  atoms 
  

   is 
  so 
  irreconcilable 
  with 
  the 
  wave 
  theory 
  of 
  the 
  nineteenth 
  century 
  

   that 
  Einstein 
  has 
  suggested 
  abandoning 
  the 
  wave 
  theory 
  of 
  light 
  

   altogether 
  and 
  returning 
  to 
  a 
  modified 
  corpuscular 
  theory 
  of 
  the 
  

   transmission 
  of 
  radiant 
  energy 
  through 
  space. 
  Also 
  at 
  the 
  hands 
  

   of 
  A. 
  H. 
  Compton 
  this 
  new 
  light-dart 
  theory 
  has 
  recently 
  had 
  new 
  

   and 
  striking 
  success, 
  but 
  nobody 
  has 
  as 
  yet 
  been 
  able 
  to 
  show 
  how 
  

   such 
  a 
  light-dart 
  theory 
  can 
  account 
  for 
  the 
  scores 
  of 
  interference 
  

   phenomena 
  so 
  beautifully 
  explained 
  by 
  the 
  wave 
  theory. 
  Such 
  is 
  the 
  

   impasse 
  confronting 
  physics 
  to-day 
  in 
  its 
  endeavor 
  to 
  obtain 
  a 
  

   picture 
  of 
  the 
  mechanism 
  of 
  the 
  transmission 
  of 
  radiant 
  energj?- 
  

   through 
  space. 
  We 
  have 
  discovered 
  a 
  whole 
  group 
  of 
  new 
  phe- 
  

   nomena 
  of 
  radiation 
  to 
  which 
  the 
  old 
  hnvs 
  do 
  not 
  apply; 
  yet 
  we 
  

   must 
  retain 
  the 
  old 
  laws 
  for 
  the 
  interpretation 
  of 
  the 
  old 
  phenomena. 
  

  

  Seventh. 
  Not 
  only 
  are 
  we 
  at 
  present 
  comiDletel}^ 
  unable 
  to 
  form 
  

   any 
  consistent 
  picture 
  of 
  the 
  mechanism 
  of 
  the 
  transmission 
  of 
  

   radiant 
  energj?-, 
  but 
  new 
  experiments 
  have 
  recently 
  come 
  to 
  light 
  

   which 
  show 
  conclusively 
  that 
  the 
  frequency 
  of 
  an 
  ether 
  wave 
  is 
  not 
  

   produced 
  by, 
  and 
  does 
  not 
  correspond 
  to, 
  a 
  synchronously 
  vibrating 
  

   electronic 
  tuning 
  fork 
  within 
  the 
  atom 
  at 
  all. 
  We 
  can 
  at 
  present 
  

   make 
  no 
  mechanical 
  picture 
  whatever 
  of 
  the 
  act 
  by 
  which 
  an 
  ether 
  

   wave 
  is 
  born 
  and 
  started 
  out 
  on 
  its 
  journey 
  through 
  space. 
  Two 
  

   electrons 
  within 
  the 
  same 
  atom 
  have 
  been 
  definitely 
  found 
  in 
  some 
  

   instances 
  to 
  jump 
  simultaneously 
  each 
  to 
  a 
  new 
  position, 
  and 
  the 
  

   sum 
  of 
  the 
  energies 
  of 
  these 
  two 
  changes 
  is 
  somehow 
  integrated 
  by 
  

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