﻿20 
  Prof. 
  L. 
  T. 
  More 
  on 
  Theories 
  

  

  mass, 
  multiplied 
  by 
  the 
  velocity 
  o£ 
  light, 
  

  

  dW 
  = 
  Ydm 
  (6)" 
  

  

  (Substituting 
  energy, 
  E, 
  for 
  momentum 
  we 
  obtain 
  

  

  ^E 
  

   ''dm=^J; 
  (7)" 
  

  

  By 
  the 
  pure 
  mathematician 
  any 
  quantity 
  of 
  an 
  equation 
  

   may 
  be 
  considered 
  either 
  as 
  a 
  constant 
  or 
  as 
  a 
  variable, 
  but 
  

   such 
  is 
  not 
  the 
  case 
  when 
  the 
  equation 
  is 
  an 
  expression 
  of 
  a 
  

   physical 
  law. 
  Quantities 
  are 
  then 
  fixed 
  as 
  constants 
  or 
  as 
  

   variables, 
  according 
  ms 
  our 
  experience 
  requires 
  them 
  to 
  be. 
  

   If 
  in 
  equation 
  (5) 
  the 
  velocity 
  of 
  light 
  is 
  said 
  to 
  be 
  a 
  constant 
  

   and 
  the 
  "mass 
  of 
  radiation" 
  a 
  variable, 
  some 
  necessity, 
  or 
  

   at 
  least 
  some 
  plausibility, 
  must 
  be 
  given 
  to 
  what 
  is 
  otherwise 
  

   an 
  arbitrary 
  assumption 
  contrary 
  to 
  our 
  ideas 
  and 
  experience. 
  

  

  One 
  might 
  eciually 
  well 
  transform 
  the 
  equation 
  for 
  potential 
  

   energy 
  

  

  into 
  the 
  differential 
  

  

  dF 
  = 
  (gh)dm, 
  

  

  and 
  declare 
  that 
  a 
  change 
  in 
  the 
  potential 
  energy 
  of 
  a 
  body 
  

   is 
  due 
  to 
  a 
  variation 
  in 
  the 
  mass 
  of 
  a 
  body 
  maintained 
  in 
  a 
  

   constant 
  position. 
  From 
  this 
  axiom 
  we 
  may 
  deduce 
  the 
  law 
  

   that 
  mass 
  is 
  a 
  function 
  of 
  the 
  position 
  of 
  a 
  body, 
  just 
  as 
  

   readily 
  as 
  Dr. 
  Lewis 
  proves 
  it 
  a 
  function 
  of 
  momentum. 
  

   The 
  only 
  difficulty 
  is 
  that 
  experience 
  teaches 
  diff'erently. 
  

   Measurements 
  of 
  the 
  velocity 
  of 
  light 
  all 
  show 
  that 
  it 
  

   decreases 
  when 
  passing 
  into 
  absorbing 
  media, 
  and 
  Nichols 
  

   and 
  Hull 
  detected 
  a 
  change 
  in 
  position 
  or 
  motion 
  of 
  a 
  body 
  

   which 
  absorbs 
  light 
  and 
  not 
  a 
  change 
  in 
  its 
  mass. 
  Nor 
  is 
  it 
  

   made 
  clear 
  how 
  the 
  quantity 
  of 
  m, 
  which 
  in 
  (5) 
  refers 
  to 
  a 
  

   beam 
  of 
  radiation, 
  later 
  is 
  the 
  mass 
  of 
  the 
  absorbing 
  body. 
  

  

  Again, 
  other 
  questions 
  arise 
  in 
  connexion 
  with 
  this 
  theory. 
  

   If 
  a 
  body, 
  emitting 
  radiant 
  energy, 
  loses 
  1*111x10"^^ 
  

   gramme 
  for 
  every 
  erg 
  expended, 
  a 
  simple 
  calculation, 
  from 
  

   the 
  estimate 
  that 
  the 
  sun 
  radiates 
  6 
  x 
  10^^ 
  calories 
  (pounds 
  per 
  

   degree 
  centigrade) 
  in 
  a 
  year, 
  gives 
  a 
  mass 
  of 
  1*2 
  x 
  10^^ 
  

   grammes 
  a 
  year 
  for 
  its 
  loss 
  in 
  mass. 
  Such 
  a 
  quantity 
  should 
  

   Lave 
  an 
  influence 
  on 
  cosmic 
  problems. 
  

  

  Another 
  difficulty 
  occurs 
  of 
  a 
  more 
  serious 
  nature. 
  The 
  

   " 
  something 
  possessing 
  mass 
  '' 
  whose 
  momentum 
  is 
  a 
  beam 
  

   of 
  radiation 
  has 
  no 
  mass 
  while 
  it 
  is 
  a 
  part 
  of 
  the 
  radiating 
  body 
  

   before 
  it 
  begins 
  its 
  journey 
  of 
  radiation. 
  In 
  the 
  free 
  sether 
  

  

  