﻿172 
  Prof. 
  J. 
  J. 
  Thomson 
  on 
  a 
  Theory 
  of 
  the 
  Connexion 
  

  

  we 
  may 
  confidently 
  assume 
  to 
  possess 
  the 
  same 
  properties 
  as 
  

   the 
  direct 
  cathodic 
  rays. 
  

  

  (c) 
  The 
  rays 
  emanating 
  from 
  the 
  posterior 
  part 
  of 
  a 
  very 
  

   thin 
  sheet, 
  the 
  anterior 
  part 
  of 
  which 
  is 
  struck 
  by 
  the 
  cathodic 
  

   rays, 
  also 
  possess 
  the 
  same 
  properties 
  as 
  these. 
  

  

  (d) 
  A 
  pencil 
  of 
  cathodic 
  rays 
  appears 
  as 
  made 
  up 
  of 
  various 
  

   rays 
  of 
  different 
  natures. 
  When 
  they 
  strike 
  on 
  a 
  substance 
  

   of 
  a 
  very 
  small 
  thickness 
  they 
  seem 
  to 
  possess 
  the 
  power 
  of 
  

   passing 
  through 
  it, 
  but 
  in 
  the 
  same 
  way 
  as 
  if 
  they 
  passed 
  

   through 
  a 
  filter, 
  which 
  would 
  allow 
  a 
  passage 
  more 
  or 
  less 
  

   easy 
  to 
  some 
  of 
  them 
  than 
  to 
  the 
  others. 
  

  

  XVII. 
  A 
  Theory 
  of 
  the 
  Connexion 
  between 
  Cathode 
  and 
  Rontgen 
  

   Rays. 
  By 
  J. 
  J. 
  Thomson, 
  M.A., 
  F.R.S., 
  Cavendish 
  Pro- 
  

   fessor 
  of 
  Experimental 
  Physics, 
  Cambridge*. 
  

  

  AMOVING 
  electrified 
  particle 
  is 
  surrounded 
  by 
  a 
  mag- 
  

   netic 
  field, 
  the 
  lines 
  of 
  magnetic 
  force 
  being 
  circles 
  

   having 
  the 
  line 
  of 
  motion 
  of 
  the 
  particle 
  for 
  axis. 
  If 
  the 
  

   particle 
  be 
  suddenly 
  stopped, 
  there 
  will, 
  in 
  consequence 
  of 
  

   electromagnetic 
  induction, 
  be 
  no 
  instantaneous 
  change 
  in 
  the 
  

   magnetic 
  field 
  ; 
  the 
  induction 
  gives 
  rise 
  to 
  a 
  magnetic 
  field, 
  

   which 
  for 
  a 
  moment 
  compensates 
  for 
  that 
  destroyed 
  by 
  the 
  

   stopping 
  of 
  the 
  particle. 
  The 
  new 
  field 
  thus 
  introduced 
  is 
  

   not, 
  however, 
  in 
  equilibrium, 
  but 
  moves 
  off 
  through 
  the 
  

   dielectric 
  as 
  an 
  electric 
  pulse. 
  In 
  this 
  paper 
  we 
  calculate 
  the 
  

   magnetic 
  force 
  and 
  electric 
  intensity 
  carried 
  by 
  the 
  pulse 
  to 
  

   any 
  point 
  in 
  the 
  dielectric. 
  

  

  The 
  distribution 
  of 
  magnetic 
  force 
  and 
  electric 
  intensity 
  

   around 
  the 
  moving 
  particle 
  depends 
  greatly 
  on 
  the 
  velocity 
  

   of 
  the 
  particle, 
  if 
  this 
  velocity 
  is 
  so 
  small 
  that 
  the 
  square 
  of 
  

   its 
  ratio 
  to 
  the 
  velocity 
  of 
  light 
  can 
  be 
  neglected, 
  then 
  the 
  

   electric 
  intensity 
  is 
  symmetrically 
  distributed 
  round 
  the 
  

   particle, 
  and 
  at 
  a 
  distance 
  r 
  from 
  it 
  is 
  equal 
  to 
  e/r* 
  2 
  , 
  where 
  e 
  

   is 
  the 
  charge 
  on 
  the 
  particle 
  ; 
  the 
  lines 
  of 
  magnetic 
  force 
  are 
  

   circles 
  with 
  the 
  line 
  of 
  motion 
  of 
  the 
  particle 
  for 
  axis 
  ; 
  the 
  

   magnitude 
  of 
  the 
  magnetic 
  force 
  at 
  a 
  point 
  P 
  is 
  ive 
  sin 
  6/r 
  2 
  , 
  

   where 
  w 
  is 
  the 
  velocity 
  of 
  the 
  particle, 
  and 
  6 
  the 
  angle 
  a 
  

   radius 
  from 
  the 
  particle 
  to 
  P 
  makes 
  with 
  the 
  direction 
  of 
  

   motion. 
  

  

  When, 
  however, 
  the 
  velocity 
  of 
  the 
  particle 
  is 
  so 
  great 
  

   that 
  we 
  can 
  no 
  longer 
  neglect 
  the 
  square 
  of 
  its 
  ratio 
  to 
  the 
  

   velocity 
  of 
  light, 
  the 
  distribution 
  of 
  electric 
  intensity 
  is 
  no 
  

   longer 
  uniform, 
  the 
  electric 
  intensity, 
  along 
  with 
  the 
  magnetic 
  

   force, 
  tends 
  to 
  concentrate 
  in 
  the 
  equatorial 
  plane, 
  that 
  is, 
  the 
  

   * 
  Communicated 
  by 
  the 
  Author. 
  

  

  