﻿126 
  Mr. 
  H. 
  S. 
  Allen 
  on 
  the 
  Relation 
  between 
  

  

  because 
  of 
  the 
  periodic 
  doubling 
  of 
  certain 
  lines 
  in 
  their 
  

   spectra. 
  Such 
  doubling 
  would 
  occur 
  owing 
  to 
  the 
  well- 
  

   known 
  Doppler 
  effect, 
  when 
  the 
  two 
  components 
  are 
  moving 
  

   one 
  away 
  from, 
  and 
  the 
  other 
  towards, 
  the 
  earth. 
  The 
  

   orbital 
  velocity 
  can 
  be 
  computed 
  from 
  the 
  separation 
  of 
  the 
  

   lines, 
  and 
  amounts 
  in 
  some 
  cases 
  to 
  as 
  much 
  as 
  150 
  miles 
  per 
  

   second 
  or 
  many 
  times 
  that 
  of 
  the 
  earth 
  in 
  its 
  orbit. 
  Now 
  

   consider 
  the 
  moment 
  when 
  the 
  two 
  components 
  are 
  in 
  the 
  line 
  

   joining 
  the 
  star 
  to 
  the 
  earth. 
  One 
  A 
  will 
  be 
  moving 
  to 
  the 
  

   right, 
  and 
  the 
  other 
  B 
  to 
  the 
  left 
  with 
  a 
  velocity 
  of 
  150 
  miles 
  

   per 
  second. 
  If 
  the 
  effect 
  of 
  motion 
  of 
  the 
  source 
  on 
  aber- 
  

   ration 
  is 
  at 
  all 
  comparable 
  with 
  that 
  of 
  motion 
  of 
  the 
  receiver, 
  

   we 
  should 
  expect 
  (when 
  the 
  light 
  then 
  leaving 
  the 
  star 
  

   reaches 
  the 
  earth) 
  to 
  see 
  star 
  A 
  displaced 
  to 
  the 
  right 
  and 
  B 
  

   to 
  the 
  left. 
  The 
  star 
  would 
  appear 
  double 
  in 
  a 
  telescope, 
  and 
  

   the 
  apparent 
  doubling 
  would 
  occur 
  periodically, 
  and 
  alter- 
  

   nately 
  with 
  the 
  separation 
  of 
  the 
  spectroscopic 
  lines. 
  That 
  

   no 
  such 
  doubling 
  is 
  seen 
  is 
  very 
  strong, 
  if 
  not 
  absolutely 
  

   conclusive 
  evidence 
  of 
  the 
  fact 
  we 
  set 
  out 
  to 
  establish, 
  that 
  

   motion 
  of 
  the 
  source 
  does 
  not 
  affect 
  aberration 
  and 
  it 
  forms 
  a 
  

   real 
  logical 
  basis 
  for 
  postulating 
  an 
  aether. 
  

  

  XII. 
  A 
  Preliminary 
  Note 
  on 
  the 
  Relation 
  between 
  Primary 
  

   and 
  Secondary 
  Kontyen 
  Radiation. 
  By 
  H. 
  S. 
  Allen, 
  

   ALA., 
  B.Sc* 
  

  

  WHEN 
  the 
  Rontgen 
  radiation 
  from 
  a 
  focus-tube 
  falls 
  

   upon 
  the 
  surface 
  of 
  certain 
  solids, 
  the 
  surface 
  becomes 
  

   the 
  source 
  of 
  a 
  secondary 
  radiation. 
  These 
  " 
  Secondary 
  

   Rontgen 
  Rays" 
  are 
  in 
  many 
  respects 
  similar 
  to 
  the 
  ordinary 
  

   rays 
  which 
  produce 
  them. 
  Their 
  properties 
  have 
  been 
  

   investigated 
  by 
  Sagnac 
  f, 
  Perrin 
  J, 
  and 
  Townsend§. 
  Both 
  

   primary 
  and 
  secondary 
  rays 
  render 
  a 
  gas 
  through 
  which 
  they 
  

   pass 
  a 
  conductor, 
  but 
  while 
  the 
  primary 
  rays 
  suffer 
  very 
  little 
  

   absorption 
  the 
  secondary 
  rays 
  are 
  almost 
  entirely 
  absorbed 
  

   within 
  a 
  few 
  millimetres 
  at 
  atmospheric 
  pressure. 
  The 
  

   object 
  of 
  the 
  present 
  investigation 
  is 
  to 
  compare 
  the 
  total 
  

   ionization 
  produced 
  by 
  the 
  secondary 
  rays 
  with 
  that 
  which 
  

   would 
  be 
  produced 
  by 
  the 
  primary 
  if 
  they 
  continued 
  their 
  

   path 
  in 
  the 
  original 
  medium. 
  Then, 
  supposing 
  that 
  the 
  total 
  

   ionization, 
  if 
  not 
  equal 
  to, 
  is 
  at 
  least 
  proportional 
  to 
  the 
  

  

  * 
  Communicated 
  by 
  Prof. 
  J. 
  J. 
  Thomson. 
  

  

  t 
  Journal 
  de 
  Physique, 
  3rd 
  series, 
  viii, 
  Feb. 
  1899. 
  

  

  J 
  Comptes 
  Rendus, 
  cxxiv. 
  p. 
  455. 
  

  

  § 
  Proc. 
  Camb. 
  Phil. 
  Soc. 
  x. 
  Part 
  iv. 
  1900. 
  

  

  