﻿Dispersion 
  of 
  Magnetic 
  Rotatory 
  Power. 
  153 
  

  

  Edgcumbe 
  and 
  Messrs. 
  Nalder 
  Bros. 
  & 
  Thompson. 
  In 
  the 
  

   former, 
  the 
  primary 
  and 
  secondary 
  windings 
  were 
  close 
  

   together, 
  giving 
  good 
  ratio 
  but 
  large 
  phase 
  displacement 
  ; 
  

   and 
  it 
  is 
  noticeable 
  that 
  throughout 
  lower 
  phase-displacement 
  

   is 
  got 
  by 
  greater 
  loss 
  o£ 
  ratio, 
  as 
  indicated 
  in 
  the 
  tests 
  on 
  the 
  

   experimental 
  transformer. 
  In 
  the 
  Nalder 
  transformer, 
  the 
  

   primary 
  and 
  secondary 
  coils 
  are 
  wound 
  on 
  thick 
  porcelain 
  

   bobbins 
  side 
  by 
  side. 
  The 
  leakage 
  is 
  therefore 
  somewhat 
  

   large, 
  producing 
  a 
  variation 
  of 
  ratio 
  of 
  about 
  8 
  per 
  cent, 
  

   between 
  2 
  and 
  18 
  amperes 
  ; 
  but 
  this 
  is 
  accompanied 
  by 
  a 
  

   phase-displacement 
  which 
  is 
  less 
  than 
  *2° 
  over 
  the 
  range 
  

   from 
  6 
  to 
  18 
  amperes 
  or 
  the 
  upper 
  two-thirds 
  of 
  the 
  range. 
  

   Such 
  a 
  transformer 
  therefore, 
  if 
  used 
  with 
  a 
  wattmeter, 
  and 
  

   calibrated 
  with 
  it, 
  should 
  do 
  fairly 
  well 
  for 
  commercial 
  

   testing. 
  

  

  In 
  conclusion 
  it 
  should 
  be 
  noted 
  that 
  the 
  tests 
  on 
  all 
  four 
  

   transformers 
  give 
  results 
  which 
  are 
  not 
  very 
  widely 
  different, 
  

   and 
  the 
  results 
  may 
  therefore 
  be 
  taken 
  as 
  fairly 
  representative 
  

   of 
  the 
  behaviour 
  of 
  instrument 
  transformers. 
  

  

  The 
  writer 
  wishes 
  to 
  express 
  his 
  thanks 
  to 
  his 
  senior 
  

   Demonstrator, 
  Mr. 
  A. 
  0. 
  Jolley, 
  for 
  great 
  assistance 
  in 
  the 
  

   experimental 
  work, 
  and 
  to 
  Mr. 
  A. 
  F. 
  Burgess, 
  B.Sc, 
  for 
  

   checking 
  the 
  calculations. 
  

  

  X. 
  On 
  the 
  Dispersion 
  of 
  Magnetic 
  Rotatory 
  Power 
  in 
  the 
  

   neighbourhood 
  of 
  Rands 
  of 
  Absorption 
  in 
  the 
  case 
  of 
  Rare 
  

   Earths. 
  Remarks 
  on 
  the 
  subject 
  of 
  recent 
  communications 
  

   by 
  Prof 
  R. 
  W. 
  Wood 
  and 
  Mr. 
  G. 
  J. 
  Elias. 
  By 
  Jean 
  

   Becquerel 
  *. 
  

  

  [Plate 
  V.] 
  

  

  THE 
  question 
  of 
  the 
  variation 
  of 
  magnetic 
  rotatory 
  power 
  

   in 
  the 
  neighbourhood 
  of 
  bands 
  of 
  absorption 
  has 
  given 
  

   rise 
  to 
  numerous 
  researches 
  and 
  stimulated 
  much 
  controversy. 
  

  

  The 
  various 
  explanations 
  of 
  the 
  phenomenon 
  of 
  magnetic 
  

   rotatory 
  polarization 
  can 
  be 
  grouped 
  into 
  two 
  principal 
  

   theories 
  f, 
  which 
  give 
  results 
  which 
  are 
  almost 
  identical 
  for 
  

   the 
  rotatory 
  dispersion 
  in 
  transparent 
  regions, 
  but 
  which 
  are 
  

   different 
  for 
  variations 
  of 
  the 
  rotatory 
  power 
  near 
  to 
  and 
  

   within 
  an 
  absorption-band. 
  

  

  According 
  to 
  " 
  the 
  molecular 
  current 
  theory 
  " 
  the 
  rotation 
  

   will 
  be 
  produced 
  in 
  opposite 
  senses 
  on 
  the 
  two 
  sides 
  of 
  a 
  

   band, 
  On 
  the 
  contrary, 
  according 
  to 
  the 
  hypothesis 
  based 
  

   on 
  the 
  Hall 
  effect, 
  the 
  rotations 
  will 
  be 
  in 
  the 
  same 
  sense 
  on 
  

  

  * 
  Communicated 
  by 
  the 
  Author. 
  

  

  f 
  See 
  Drude, 
  Lehrbuch 
  der 
  Optik, 
  1906, 
  p. 
  406. 
  

  

  