﻿into 
  the 
  'Skin 
  y 
  -effect 
  in 
  Electrical 
  Oscillators. 
  429 
  

  

  4,770,000 
  for 
  electric-light 
  carbon, 
  we 
  obtain 
  the 
  following 
  

  

  table 
  :— 
  

  

  Table 
  I. 
  

  

  Frequency 
  

  

  Thickness 
  of 
  Skin.' 
  

  

  Copper. 
  

  

  Platinum. 
  

  

  Carbon. 
  

  

  Millions. 
  

   375 
  

  

  825 
  

  

  2000 
  

  

  3200 
  

  

  cm. 
  

   000033 
  

  

  000022 
  

  

  000014 
  

  

  0-00011 
  

  

  cm. 
  

   0-00002 
  

  

  cm. 
  

   0-01749 
  

  

  We 
  can 
  obtain 
  an 
  approximate 
  value 
  for 
  the 
  thickness 
  of 
  

   the 
  c 
  skin 
  ; 
  in 
  another 
  way. 
  Suppose 
  the 
  conductor 
  to 
  be 
  a 
  

   circular 
  cylinder. 
  From 
  Stefan's 
  formula 
  (2) 
  

  

  I— 
  \/? 
  

  

  and 
  assuming 
  that, 
  as 
  with 
  steady 
  currents, 
  the 
  resistance 
  is 
  

   inversely 
  proportional 
  to 
  the 
  area 
  of 
  the 
  section 
  used 
  by 
  the 
  

   current, 
  the 
  oscillatory 
  current 
  must 
  occupy 
  the 
  R/U'th 
  part 
  

  

  of 
  the 
  section. 
  Since 
  this 
  portion 
  is 
  

   surface 
  we 
  have 
  

  

  2irax 
  = 
  yy, 
  x 
  7ra 
  2 
  , 
  

  

  thin 
  laver 
  next 
  the 
  

  

  and 
  

  

  / 
  ItfX 
  

  

  = 
  ™V 
  "a 
  X 
  

   r 
  = 
  1 
  /T 
  ; 
  

  

  27T 
  V 
  tip 
  

  

  which 
  turns 
  out 
  to 
  be 
  precisely 
  the 
  value 
  we 
  obtained 
  before 
  

  

  (id. 
  

  

  Hertz 
  * 
  stated 
  that, 
  as 
  far 
  as 
  he 
  could 
  observe, 
  the 
  nature 
  

   of 
  the 
  metal 
  out 
  of 
  which 
  his 
  resonator 
  was 
  formed 
  had 
  no 
  

   influence 
  upon 
  the 
  phenomena, 
  but 
  experiments 
  by 
  Bjerknesf 
  

   did 
  not 
  confirm 
  this 
  conclusion. 
  He 
  found 
  the 
  efficiency 
  of 
  

   the 
  metals 
  copper, 
  brass, 
  silver, 
  platinum, 
  nickel, 
  iron, 
  to 
  be 
  

   in 
  the 
  order 
  in 
  which 
  they 
  are 
  here 
  named. 
  By 
  depositing 
  

  

  * 
  ' 
  Electric 
  Waves,' 
  p. 
  45. 
  

  

  t 
  Wied. 
  Ann. 
  xlviii. 
  p. 
  592 
  (1893). 
  

  

  