﻿532 
  Dr. 
  Gr. 
  Johnstone 
  Stoney 
  on 
  Evidence 
  

  

  value 
  of 
  1 
  — 
  2rc 
  decreases. 
  Hence 
  an 
  upper 
  limit 
  may 
  be 
  

   obtained 
  by 
  putting 
  1 
  — 
  2n 
  equal 
  to 
  its 
  value 
  at 
  the 
  lower 
  

   temperature 
  limit, 
  and 
  we 
  may 
  write 
  

  

  «=— 
  (l-*»)«lfo-*l). 
  

  

  To 
  take 
  a 
  very 
  favourable 
  case, 
  we 
  may 
  suppose 
  the 
  

  

  electrolyte 
  to 
  be 
  LiOH. 
  Here 
  we 
  have 
  for 
  18° 
  C. 
  1 
  — 
  2n 
  = 
  '7. 
  

   p 
  

  

  ft) 
  = 
  1, 
  and 
  — 
  = 
  "0000867 
  when 
  e 
  is 
  expressed 
  in 
  volts. 
  Taking 
  

  

  ^2"~^i 
  = 
  100 
  as 
  a 
  fairly 
  extreme 
  temperature-interval, 
  we 
  get 
  

   * 
  = 
  -006 
  volt. 
  

  

  This 
  rough 
  calculation 
  shows 
  that 
  in 
  the 
  case 
  of 
  salt- 
  

   solutions 
  the 
  maximum 
  initial 
  potential-difference 
  arising 
  

   from 
  the 
  Thomson 
  effect 
  would 
  only 
  amount, 
  under 
  ordinary 
  

   conditions, 
  to 
  a 
  few 
  thousandths 
  of 
  a 
  volt 
  at 
  the 
  most. 
  This 
  

   result 
  justifies 
  the 
  neglecting 
  of 
  the 
  Thomson 
  P.D. 
  in 
  the 
  

   measurement 
  of 
  thermo-electric 
  cells, 
  except 
  when 
  the 
  experi- 
  

   mental 
  error 
  is 
  less 
  than 
  one-thousandth 
  of 
  a 
  volt. 
  

   Holywood, 
  Co. 
  Down, 
  April 
  1898. 
  

  

  LVII. 
  Evidence 
  that 
  JRontgen 
  Rays 
  are 
  Ordinary 
  Light. 
  

   By 
  G. 
  Johnstone 
  Stoney, 
  M.A., 
  D.Sc, 
  FM.S* 
  

  

  TN 
  4 
  Nature 
  ' 
  of 
  the 
  28th 
  of 
  last 
  April, 
  p. 
  607, 
  Lord 
  Ray- 
  

   JL 
  leigh 
  calls 
  attention 
  to 
  the 
  fact 
  that 
  under 
  Sir 
  Greorge 
  

   Stokes's 
  theory 
  of 
  Rontgen 
  rays 
  — 
  that 
  which 
  is 
  known 
  as 
  

   the 
  hedge-firing 
  theory 
  — 
  we 
  are 
  justified 
  in 
  expecting 
  a 
  large 
  

   proportion 
  of 
  ordinary 
  light 
  of 
  short 
  wave-length 
  in 
  the 
  

   radiation 
  from 
  the 
  shield 
  which 
  receives 
  and 
  arrests 
  the 
  

   " 
  kathode 
  rays." 
  This 
  he 
  infers 
  generally 
  from 
  the 
  properties 
  

   of 
  Fourier's 
  theorem, 
  without 
  entering 
  into 
  the 
  details 
  which 
  

   seem 
  necessary 
  ; 
  and 
  I 
  understand 
  him 
  accordingly 
  to 
  put 
  

   forward 
  the 
  conclusion 
  as 
  an 
  opinion 
  we 
  are 
  justified 
  in 
  

   strongly 
  holding, 
  though 
  not 
  actually 
  proved. 
  It 
  may 
  

   therefore 
  not 
  be 
  useless 
  to 
  publish 
  a 
  proof 
  which 
  the 
  present 
  

   writer 
  had 
  worked 
  out 
  for 
  his 
  own 
  satisfaction. 
  An 
  explicit 
  

   proof 
  seems 
  the 
  more 
  desirable 
  inasmuch 
  as 
  Fourier's 
  

   theorem, 
  except 
  where 
  it 
  can 
  be 
  applied 
  throughout 
  to 
  the 
  

   actual 
  conditions 
  which 
  exist 
  in 
  nature, 
  furnishes 
  only 
  

   kinematical 
  resolutions 
  which 
  may 
  differ 
  materially 
  from 
  

   the 
  actual 
  physical 
  resolutions 
  effected 
  by 
  nature 
  f. 
  

  

  * 
  Communicated 
  by 
  the 
  Author. 
  

  

  t 
  For 
  example, 
  all 
  the 
  resolutions 
  effected 
  by 
  Fourier's 
  theorem 
  in 
  the 
  

   paper 
  beginning- 
  on 
  p. 
  281 
  of 
  the 
  Phil. 
  Mag. 
  for 
  April 
  1897, 
  are 
  of 
  this 
  

   illusory 
  kind. 
  The 
  component 
  motions 
  furnished 
  by 
  that 
  investigation 
  

   do 
  not 
  fulfil 
  the 
  necessary 
  condition 
  that 
  each 
  separately 
  can 
  he 
  propa- 
  

   gated 
  by 
  the 
  medinm. 
  

  

  