﻿164 
  Prof. 
  Q. 
  Majorana 
  on 
  the 
  Second 
  

  

  an 
  extension 
  justified 
  by 
  the 
  negative 
  results 
  of 
  certain 
  ex- 
  

   periments 
  (Michel 
  son 
  and 
  Morley, 
  Trouton 
  and 
  Noble) 
  by 
  

   which 
  it 
  was 
  sought 
  to 
  discover 
  the 
  absolute 
  motion 
  of 
  the 
  

   earth, 
  or 
  the 
  (Ethereal 
  wind 
  which 
  must 
  traverse 
  all 
  terrestrial 
  

   objects. 
  The 
  second 
  postulate 
  is 
  the 
  generalization 
  of 
  a 
  

   fundamental 
  principle 
  in 
  the 
  theory 
  of 
  sethereal 
  or 
  electro- 
  

   magnetic 
  undulations. 
  

  

  But 
  if 
  these 
  two 
  principles, 
  derived 
  from 
  quite 
  different 
  

   chapters 
  of 
  physics, 
  have 
  been 
  fully 
  accepted 
  severally 
  by 
  

   modern 
  physicists, 
  their 
  origin 
  has 
  been 
  almost 
  forgotten 
  ; 
  

   an 
  ingenious 
  structure 
  arose 
  upon 
  their 
  union 
  : 
  the 
  theory 
  

   of 
  relativity. 
  This 
  theory, 
  while 
  repudiating 
  according 
  to 
  

   Einstein 
  and 
  others 
  a 
  theoretical 
  conception 
  which 
  had 
  given 
  

   occasion 
  for 
  the 
  formulation 
  of 
  the 
  second 
  postulate 
  (the 
  

   aether), 
  serves 
  well 
  to 
  explain 
  the 
  insuccess 
  of 
  the 
  above- 
  

   cited 
  experiments. 
  

  

  Now 
  our 
  imagination, 
  accustomed, 
  as 
  W. 
  Ritz 
  has 
  said, 
  

   to 
  " 
  substantialize 
  " 
  physical 
  phenomena, 
  if 
  it 
  easily 
  grasps 
  

   the 
  essence 
  of 
  the 
  first 
  postulate, 
  does 
  not 
  do 
  so 
  in 
  the 
  case 
  

   of 
  the 
  second 
  ; 
  and 
  the 
  more 
  so 
  since, 
  as 
  has 
  already 
  been 
  

   said, 
  some 
  adherents 
  to 
  relativistic 
  theories 
  do 
  not 
  retain 
  as 
  

   necessary 
  the 
  existence 
  of 
  a 
  medium 
  of 
  transmission 
  (the 
  

   aether) 
  in 
  order 
  to 
  explain 
  the 
  constancy 
  of 
  c. 
  Moreover 
  on 
  

   the 
  second 
  postulate, 
  or, 
  more 
  precisely, 
  on 
  a 
  certain 
  portion 
  

   of 
  this, 
  depend 
  the 
  conclusions 
  which 
  appear 
  artificial 
  or 
  

   extraordinary 
  in 
  the 
  whole 
  relativistic 
  theory 
  *. 
  The 
  second 
  

   postulate 
  must 
  be 
  understood 
  in 
  the 
  sense 
  that 
  an 
  observer 
  

   who 
  measures 
  the 
  velocity 
  of 
  light 
  finds 
  always 
  the 
  same 
  

   value 
  if 
  both 
  he 
  and 
  the 
  source 
  be 
  at 
  rest, 
  relative 
  or 
  (if 
  the 
  

   possibility 
  be 
  admitted) 
  absolute, 
  or 
  if 
  the 
  source 
  or 
  the 
  

   observer, 
  or 
  both, 
  have 
  a 
  uniform 
  motion 
  of 
  translation. 
  In 
  

   short, 
  the 
  second 
  postulate 
  affirms 
  the 
  absolute 
  independence 
  

   of 
  c 
  of 
  any 
  contingency 
  whatever 
  of 
  uniform 
  motion 
  of 
  

   translation 
  of 
  the 
  source 
  or 
  of 
  the 
  observer. 
  

  

  It 
  is 
  known 
  that 
  an 
  hypothesis 
  of 
  a 
  mechanical 
  character 
  

   (emissive 
  or 
  ballistic), 
  according 
  to 
  which 
  to 
  the 
  ordinary 
  

   velocity 
  of 
  light 
  must 
  be 
  added 
  that 
  of 
  the 
  source, 
  can 
  

   explain, 
  like 
  the 
  theory 
  of 
  relativity, 
  the 
  failure 
  of 
  the 
  above- 
  

   quoted 
  experiments. 
  But 
  this 
  hypothesis 
  is 
  radically 
  in 
  

   contrast 
  with 
  the 
  electromagnetic 
  theory, 
  and 
  consequently 
  

   is 
  not 
  much 
  favoured 
  f- 
  But 
  in 
  any 
  case 
  laboratory 
  experi- 
  

   ments 
  can 
  be 
  conceived 
  which 
  should 
  decide 
  between 
  the 
  

  

  * 
  Carmichael, 
  Phys. 
  Eev. 
  xxxv. 
  p. 
  168 
  (1912). 
  

  

  t 
  In 
  this 
  connexion 
  should 
  be 
  recalled 
  the 
  important 
  critical 
  work 
  of 
  

   W. 
  Ritz 
  ((Euvres, 
  p. 
  317) 
  which 
  perhaps 
  has 
  not 
  been 
  taken 
  into 
  suffi- 
  

   cient 
  consideration 
  by 
  physicists. 
  

  

  