﻿in 
  Iron 
  hy 
  Rapidly 
  Oscillating 
  Current 
  -fields. 
  507 
  

  

  Rayleigh's 
  method 
  was 
  employed 
  for 
  determining 
  the 
  

   largest 
  self-induction 
  (137 
  x 
  10 
  6 
  cms.) 
  used. 
  

  

  The 
  other 
  self-inductions, 
  including 
  those 
  of 
  the 
  sets 
  of 
  

   solenoids, 
  were 
  too 
  small 
  to 
  enable 
  Rayleigh's 
  method 
  to 
  be 
  

   applied, 
  and 
  were 
  not 
  of 
  a 
  form 
  to 
  permit 
  the 
  use 
  of 
  Max- 
  

   well's 
  formula; 
  so 
  advantage 
  was 
  taken 
  of 
  the 
  deflexion 
  of 
  the 
  

   cathode-rays 
  by 
  the 
  oscillatory 
  currents 
  produced 
  by 
  the 
  

   leyden-jar 
  discharges, 
  to 
  compare 
  them 
  with 
  the 
  standard 
  

   self-inductions 
  given 
  above. 
  As 
  we 
  have 
  already 
  seen, 
  the 
  

   deflexion 
  due 
  to 
  the 
  oscillatory 
  current 
  is 
  proportional 
  to 
  

  

  'V\/-r'i 
  if 
  now 
  the 
  sparking 
  distance 
  and 
  capacity 
  are 
  kept 
  

  

  constant, 
  the 
  deflexion 
  is 
  inversely 
  proportional 
  to 
  the 
  square 
  

   root 
  of 
  L. 
  

  

  To 
  determine, 
  for 
  example, 
  the 
  self-induction 
  of 
  the 
  three 
  

   coils 
  of 
  the 
  first 
  (or 
  615 
  turn) 
  system 
  of 
  solenoids, 
  placed 
  in 
  

   series, 
  by 
  comparison 
  with 
  the 
  standard 
  coils 
  I. 
  and 
  II. 
  : 
  — 
  

   Let 
  a 
  be 
  the 
  deflexion 
  when 
  only 
  the 
  three 
  solenoids 
  are 
  

   in 
  the 
  secondary 
  circuit, 
  no 
  other 
  self-induction 
  being 
  

   in 
  circuit 
  *; 
  

   /3 
  the 
  deflexion 
  when 
  in 
  addition 
  the 
  standard 
  coil 
  I. 
  is 
  in 
  

   circuit, 
  and 
  y 
  the 
  deflexion 
  when 
  this 
  is 
  replaced 
  by 
  

   the 
  standard 
  coil 
  II. 
  

   Then 
  L= 
  8xl0 
  6 
  _ 
  22xl0 
  6 
  

  

  ~(i)'-M?)'-'' 
  

  

  The 
  following 
  table 
  gives 
  the 
  deflexions 
  actually 
  observed. 
  

   Table 
  III. 
  

  

  a. 
  

  

  fL 
  

  

  r- 
  

  

  L 
  in 
  cms. 
  as 
  determined 
  with 
  

  

  Standard 
  Coil 
  I. 
  Standard 
  Coil 
  II. 
  

  

  66 
  

   65 
  

   1 
  63 
  

   61 
  

   63 
  

   70 
  

   70 
  

   47 
  

   51 
  

  

  50 
  

   49 
  

   48 
  

   47 
  

   48 
  

   54 
  

   53 
  

   37 
  

   40 
  

  

  38 
  

   38 
  

   37 
  

   37 
  

   37 
  

   42 
  

   41 
  

   28 
  

   30 
  

  

  11-2x10° 
  

   105 
  „ 
  

   HI 
  „ 
  

   11-7 
  „ 
  

   ll'l 
  „ 
  

   H-8 
  „ 
  

   108 
  „ 
  

   130 
  „ 
  

   12-8 
  „ 
  

  

  11-2x10° 
  

   11-4 
  „ 
  

   11-6 
  „ 
  

   12'8 
  „ 
  

   11-6 
  „ 
  

   124 
  „ 
  

   11-5 
  „ 
  

   12-0 
  ., 
  

   116 
  „ 
  

  

  Mean 
  values 
  for 
  L 
  1T5X 
  10° 
  118x 
  10" 
  

  

  * 
  Note. 
  Two 
  of 
  the 
  three 
  solenoids 
  were 
  used 
  to 
  deflect 
  the 
  rays 
  

  

  see 
  sketch. 
  

  

  