﻿166 
  Prof. 
  Q. 
  Majorana 
  on 
  the 
  Second 
  

  

  hypotheses, 
  and 
  these 
  values 
  differ 
  by 
  a 
  term 
  of 
  the 
  first 
  

   order 
  in 
  ft. 
  If 
  then 
  the 
  Doppler 
  effect 
  is 
  measured, 
  by 
  

   observation 
  of 
  the 
  wave-length, 
  different 
  results 
  should 
  be 
  

   obtained 
  according 
  as 
  the 
  one 
  or 
  the 
  other 
  hypothesis 
  is 
  

   adopted*. 
  Now 
  observations 
  of 
  the 
  Doppler 
  effect 
  have 
  

   already 
  been 
  made 
  by 
  measuring 
  the 
  displacement 
  of 
  the 
  

   spectral 
  lines, 
  employing 
  either 
  prisms 
  or 
  diffraction-gratings. 
  

   In 
  the 
  case 
  of 
  prisms 
  it 
  may 
  be 
  observed 
  that 
  all 
  the 
  theories 
  

   of 
  dispersion 
  hitherto 
  admitted 
  lead 
  to 
  the 
  supposition 
  that 
  

   this 
  phenomenon 
  can 
  only 
  depend 
  on 
  the 
  frequency 
  of 
  the 
  

   incident 
  luminous 
  vibrations. 
  Consequently 
  the 
  displace- 
  

   ment 
  of 
  the 
  spectral 
  lines 
  may 
  be 
  caused 
  by 
  the 
  simple 
  

   variation 
  in 
  frequency 
  due 
  to 
  the 
  Doppler 
  effect, 
  and 
  this 
  

   whether, 
  for 
  the 
  light, 
  the 
  hypothesis 
  of 
  a 
  stationary 
  aether 
  is 
  

   adopted, 
  or 
  a 
  ballistic 
  or 
  emissive 
  theory. 
  From 
  this 
  point 
  

   of 
  view, 
  therefore, 
  the 
  question 
  whether 
  the 
  velocity 
  of 
  

   propagation 
  of 
  the 
  light 
  emitted 
  by 
  a 
  source 
  does 
  or 
  does 
  

   not 
  change 
  with 
  the 
  velocity 
  of 
  the 
  latter 
  remains 
  unanswered. 
  

   But 
  the 
  Doppler 
  effect 
  has 
  been 
  established 
  with 
  diffraction- 
  

   gratings 
  as 
  well 
  as 
  with 
  prisms, 
  and 
  for 
  astronomical 
  as 
  well 
  

   as 
  terrestrial 
  sources 
  f. 
  Now 
  the 
  function 
  of 
  a 
  grating, 
  from 
  

   the 
  geometrical 
  point 
  of 
  view, 
  may 
  be 
  regarded 
  as 
  depending 
  

   exclusively 
  on 
  the 
  values 
  of 
  the 
  incident 
  wave-lengths 
  ; 
  the 
  

   positions 
  of 
  the 
  successive 
  spectral 
  lines 
  remain 
  exactly 
  

   determined 
  by 
  those 
  values. 
  But 
  since, 
  according 
  to 
  the 
  

   ballistic 
  or 
  emissive 
  hypothesis, 
  the 
  value 
  of 
  X 
  does 
  not 
  vary 
  

   with 
  the 
  velocity 
  of 
  the 
  source, 
  we 
  see 
  that 
  the 
  grating 
  

   should 
  not 
  give 
  an 
  appreciable 
  result 
  in 
  the 
  study 
  of 
  the 
  

   Doppler 
  effect, 
  and 
  this, 
  as 
  is 
  known, 
  is 
  not 
  in 
  agreement 
  

   with 
  experience. 
  We 
  may 
  then 
  conclude 
  from 
  observations 
  

   of 
  the 
  Doppler 
  phenomenon 
  in 
  the 
  stars 
  and 
  the 
  limb 
  of 
  the 
  

   sun 
  with 
  moving 
  mirrors 
  (Galitzin 
  & 
  Wilip), 
  or 
  again 
  in 
  

   the 
  canal 
  rays 
  (Stark, 
  Paschen), 
  that 
  the 
  velocity 
  of 
  light 
  is 
  

   absolutely 
  constant 
  and 
  independent 
  of 
  the 
  movement 
  of 
  the 
  

   source 
  ; 
  this 
  is 
  equivalent 
  to 
  the 
  rejection 
  of 
  the 
  ballistic 
  or 
  

   emissive 
  theory. 
  This 
  is 
  Tolman's 
  opinion 
  {, 
  in 
  contradiction 
  

   to 
  that 
  of 
  Stewart 
  §. 
  Indeed, 
  it 
  should 
  be 
  borne 
  in 
  mind 
  

   that 
  the 
  ordinary 
  grating 
  theory 
  || 
  may 
  not 
  apply 
  exactly 
  in 
  

   the 
  case 
  of 
  a 
  mechanical 
  (ballistic 
  or 
  emissive) 
  theory 
  of 
  

  

  * 
  These 
  conclusions 
  are 
  identical 
  with 
  those 
  already 
  published 
  by 
  

   other 
  authors 
  ; 
  see, 
  e. 
  g., 
  Tolman, 
  Phys. 
  Rev. 
  xxi. 
  p. 
  26 
  (1910). 
  

  

  f 
  Galitzin 
  & 
  Wilip, 
  Communications 
  Ace. 
  Musse, 
  1907, 
  p. 
  213 
  : 
  Stark, 
  

   Ann. 
  d. 
  Phys. 
  xxviii. 
  p. 
  974 
  (1909). 
  

  

  t 
  Phys. 
  Rev. 
  xxxv. 
  p. 
  136 
  (1912). 
  

  

  § 
  Phys. 
  Rev. 
  xxxii. 
  p. 
  418 
  (1911). 
  

  

  i| 
  La 
  Rosa, 
  Nuovo 
  Cimento, 
  iii. 
  p. 
  356 
  (1912). 
  

  

  