﻿in 
  Positive 
  Rays 
  in 
  Hydrogen. 
  899 
  

  

  the 
  values 
  for 
  different 
  spectral 
  lines 
  were 
  made 
  but 
  a 
  little 
  

   smaller. 
  

  

  The 
  observed 
  values 
  of 
  the 
  velocities 
  are 
  given 
  in 
  the 
  

   following 
  table. 
  

  

  Table 
  II. 
  

   Cathode 
  Falls 
  2650 
  volts. 
  Length 
  of 
  dark 
  space 
  3*0 
  cm. 
  

  

  Telocity 
  of 
  rays 
  

   the 
  cathode, 
  

  

  i 
  

  

  approaching 
  

   cm. 
  sec. 
  

  

  Velocity 
  of 
  reflected 
  rays 
  

   in 
  cm./sec. 
  

  

  

  Minimum. 
  

  

  Densest 
  portion. 
  

  

  Minimum. 
  

  

  Densest 
  portion. 
  

  

  

  1-20x107 
  

  

  1-43 
  

  

  1-49 
  

  

  1-41x107 
  

  

  1-46 
  

  

  1-40 
  

  

  rooxiO' 
  

  

  1-34 
  

  

  1-21x107 
  

   1-31 
  

  

  It 
  is 
  seen 
  that 
  the 
  minimum 
  velocity 
  is 
  not 
  constant 
  for 
  

   different 
  wavelengths, 
  the 
  differences 
  being 
  rather 
  larger 
  

   than 
  the 
  errors 
  of 
  measurement. 
  Since 
  H^ 
  generally 
  

   appears 
  on 
  the 
  photographic 
  plates 
  weaker 
  than 
  H^ 
  and 
  

   stronger 
  than 
  H.y, 
  the 
  result 
  cannot 
  be 
  explained 
  as 
  a 
  photo- 
  

   graphic 
  effect. 
  The 
  minimum 
  velocity 
  is 
  approximately 
  

   inverselv 
  proportional 
  to 
  the 
  square 
  root 
  of 
  the 
  wavelength, 
  

   the 
  product 
  of 
  these 
  two 
  quantities 
  having 
  the 
  following 
  

   values. 
  

  

  (rays 
  approaching 
  (reflected 
  rays), 
  

   the 
  cathode). 
  

  

  forH„ 
  97-1 
  85-0 
  

  

  H^ 
  99-7 
  93-4 
  

  

  H,^ 
  98-1 
  

  

  Stark 
  and 
  Steubing 
  * 
  have 
  found 
  this 
  law 
  to 
  hold 
  for 
  the 
  

   minimum 
  velocity 
  behind 
  the 
  cathode. 
  In 
  front 
  of 
  the 
  

   cathode, 
  although 
  the 
  light 
  is 
  fainter, 
  there 
  is 
  the 
  advantage 
  

   that 
  the 
  edge 
  of 
  the 
  shifted 
  line 
  is 
  sharper. 
  

  

  The 
  variations 
  in 
  the 
  measurements 
  of 
  the 
  velocity 
  corre- 
  

   sponding 
  to 
  the 
  densest 
  portion 
  of 
  the 
  shifted 
  line 
  do 
  not 
  lie 
  

   outside 
  the 
  limits 
  of 
  the 
  errors 
  of 
  measurement. 
  

  

  * 
  Stark 
  and 
  Steubing, 
  Ann. 
  d. 
  Phys. 
  xxviii. 
  p. 
  974 
  (1909). 
  

  

  