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  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1927 
  

  

  Note 
  that 
  these 
  properties 
  are 
  completely 
  independent 
  of 
  all 
  theories 
  

   as 
  to 
  the 
  nature 
  of 
  electromagnetic 
  waves. 
  - 
  

  

  We 
  can 
  produce 
  and 
  study 
  electromagnetic 
  waves 
  of 
  an 
  infinite 
  

   variety 
  of 
  frequencies 
  ranging 
  from 
  very 
  long 
  wireless 
  waves, 
  kilo- 
  

   meters 
  long, 
  up 
  through 
  heat 
  waves 
  to 
  light 
  waves 
  of 
  wave 
  length 
  

   of 
  the 
  order 
  of 
  t^-ottit 
  mm., 
  up 
  still 
  farther 
  through 
  ultra-violet 
  rays 
  

   to 
  X 
  rays 
  of 
  frequencies 
  10,000 
  times 
  that 
  of 
  ordinary 
  light, 
  and 
  

   up 
  again 
  through 
  gamma 
  rays 
  to 
  the 
  cosmic 
  rays 
  of 
  frequencies 
  again 
  

   1,000 
  times 
  those 
  of 
  X 
  rays. 
  All 
  this 
  to 
  show 
  that 
  the 
  physics 
  of 
  

   the 
  ether 
  is 
  not 
  a 
  vague 
  set 
  of 
  ideas 
  but 
  that 
  it 
  deals 
  with 
  sharply 
  

   measurable 
  experimental 
  facts, 
  the 
  validity 
  of 
  which 
  is 
  unquestioned, 
  

   and 
  which 
  are 
  completely 
  independent 
  of 
  all 
  speculations 
  and 
  theories. 
  

  

  Now, 
  if 
  in 
  1890 
  any 
  physicist 
  had 
  been 
  asked 
  to 
  describe 
  the 
  mode 
  

   of 
  interaction 
  between 
  ether 
  waves, 
  and, 
  say, 
  electrons 
  in 
  atoms, 
  he 
  

   would 
  presumably 
  have 
  answered 
  with 
  great 
  definiteness 
  and 
  assur- 
  

   ance 
  about 
  as 
  follows 
  : 
  

  

  It 
  is 
  essentially 
  the 
  same 
  as 
  the 
  mode 
  of 
  interaction 
  between 
  a 
  timing 
  fork, 
  

   or 
  a 
  piano 
  string, 
  and 
  the 
  air 
  waves 
  produced 
  by 
  its 
  vibration. 
  The 
  fork 
  

   sends 
  out 
  into 
  the 
  surrounding 
  air 
  a 
  series 
  of 
  waves 
  the 
  period 
  of 
  which 
  

   of 
  course 
  synelirouizes 
  witli 
  the 
  peritxl 
  of 
  the 
  vibrating 
  prong. 
  If 
  just 
  such 
  

   a 
  series 
  of 
  waves 
  should 
  fall 
  upon 
  the 
  fork 
  when 
  at 
  rest 
  it 
  would 
  pick 
  up 
  

   these 
  waves 
  and 
  be 
  set 
  into 
  vibration 
  by 
  them. 
  But 
  this 
  would 
  be 
  true 
  when, 
  

   and 
  only 
  when, 
  the 
  frequency 
  of 
  the 
  impressed 
  or 
  on-coming 
  waves 
  coincides 
  

   with 
  the 
  natural 
  frequency 
  of 
  the 
  tuning 
  fork. 
  Precisely 
  similarly 
  the 
  elec- 
  

   trical 
  charges 
  — 
  now 
  called 
  electrons 
  — 
  which 
  are 
  in 
  the 
  atoms 
  of 
  matter 
  when 
  

   these 
  atoms 
  are 
  for 
  example 
  in 
  the 
  suns 
  and 
  stars, 
  are 
  set 
  into 
  all 
  sorts 
  of 
  rapid 
  

   vibrati(ms 
  and 
  these 
  vibrating 
  electrical 
  bodies 
  impress 
  their 
  individual, 
  or 
  

   better 
  their 
  integrated, 
  wave 
  form 
  upon 
  the 
  ether 
  just 
  exactly 
  as 
  the 
  instruments 
  

   of 
  the 
  orchestra 
  impress 
  their 
  integrated 
  wave 
  form 
  upon 
  the 
  air 
  which 
  trans- 
  

   mits 
  it 
  to 
  your 
  ear. 
  

  

  Now 
  up 
  to 
  1900 
  all 
  the 
  phenomena 
  of 
  ether 
  waves 
  had 
  seemed 
  to 
  

   fit 
  accurately 
  and 
  beautifully 
  into 
  this 
  sort 
  of 
  wave 
  theory. 
  Its 
  

   succcesses 
  were 
  almost 
  countless. 
  It 
  explained 
  beautiful 
  and 
  intri- 
  

   cate 
  phenomena 
  like 
  the 
  colors 
  of 
  soap 
  bubbles 
  and 
  interference 
  

   patterns 
  of 
  even 
  the 
  most 
  complicated 
  sort. 
  Up 
  to 
  1900, 
  I 
  say, 
  the 
  

   theory 
  had 
  never 
  failed. 
  But 
  during 
  the 
  first 
  15 
  years 
  of 
  this 
  

   century 
  there 
  was 
  discovered 
  a 
  group 
  of 
  new 
  phenomena 
  which 
  

   baiiled 
  explanation 
  in 
  terms 
  of 
  nineteenth 
  century 
  ether 
  physics. 
  

   These 
  phenomena 
  are 
  as 
  follows: 
  When 
  ether 
  waves 
  of 
  sufficiently 
  

   high 
  frequency 
  are 
  allowed 
  to 
  fall 
  upon 
  the 
  atoms 
  of 
  matter 
  they 
  are 
  

   found 
  to 
  jerk 
  the 
  electrons 
  from 
  these 
  atoms, 
  and 
  in 
  so 
  doing 
  to 
  com- 
  

   municate 
  to 
  them 
  a 
  kinetic 
  energy 
  which 
  is 
  independent 
  of 
  the 
  inten- 
  

   sity 
  of 
  the 
  incident 
  waves, 
  but 
  is 
  accurately 
  proportional 
  to 
  their 
  

   frequency; 
  i. 
  e., 
  kinetic 
  energy 
  imparted=^= 
  A 
  v 
  — 
  ^ 
  where 
  A 
  is 
  a 
  uni- 
  

   versal 
  constant, 
  v 
  the 
  frequency 
  of 
  the 
  incident 
  waves, 
  and 
  p 
  the 
  work 
  

   necessary 
  to 
  detach 
  the 
  electron 
  from 
  the 
  metal. 
  This 
  is 
  a, 
  phenom- 
  

   enon 
  that 
  has 
  been 
  checked 
  in 
  all 
  sorts 
  of 
  ways 
  and 
  has 
  always 
  and 
  

  

  