﻿Bancs 
  — 
  Trial 
  of 
  Interferential 
  Induction 
  oalance. 
  Ill 
  

  

  number 
  of 
  equidistant 
  small 
  holes 
  cut 
  near 
  the 
  margin. 
  

   Mounted 
  on 
  an 
  axle 
  and 
  rotated 
  by 
  a 
  small 
  electromotor, 
  it 
  was 
  

   supposed 
  that 
  the 
  speed 
  could 
  be 
  regulated 
  nearly 
  enough 
  by 
  

   inserting 
  resistances. 
  I 
  did 
  not 
  have 
  any 
  success 
  with 
  this 
  

   disc. 
  Though 
  I 
  was 
  able 
  to 
  increase 
  the 
  flashes 
  to 
  3000 
  per 
  

   second, 
  they 
  were 
  never 
  instantaneous 
  enough 
  for 
  the 
  work, 
  

   even 
  when 
  the 
  holes 
  were 
  reduced 
  to 
  an 
  extreme 
  of 
  smallness. 
  

   It 
  ought 
  not 
  to 
  be 
  difficult, 
  however, 
  to 
  reach 
  the 
  end 
  in 
  view 
  

   by 
  replacing 
  the 
  sodium 
  flame 
  F 
  by 
  a 
  hydrogen 
  G-eissler 
  

   tube. 
  The 
  light 
  would 
  have 
  to 
  be 
  analyzed 
  prismatically 
  and 
  

   the 
  period 
  of 
  intermittance 
  suitably 
  chosen. 
  Michelson* 
  has 
  

   shown 
  that 
  the 
  lines 
  of 
  the 
  hydrogen 
  spectrum 
  are 
  not 
  well 
  

   adapted 
  for 
  refined 
  refractometer 
  work. 
  In 
  the 
  present 
  case 
  

   the 
  number 
  of 
  fringes 
  in 
  question 
  is 
  only 
  a 
  very 
  few 
  (2 
  or 
  3), 
  

   so 
  that 
  I 
  do 
  not 
  think 
  there 
  will 
  be 
  difficulty 
  for 
  this 
  reason. 
  

  

  5. 
  The 
  apparatus 
  being 
  differential 
  in 
  type, 
  is 
  particularly 
  

   adapted 
  for 
  observing 
  the 
  Joule 
  expansion 
  phenomenon, 
  its 
  

   variation 
  with 
  the 
  field, 
  with 
  temperature 
  and 
  dimensions 
  of 
  

   the 
  core, 
  etc. 
  The 
  results 
  of 
  the 
  table 
  are 
  random 
  examples 
  

   among 
  many 
  data 
  obtained 
  with 
  continuous 
  currents. 
  The 
  

   first 
  column 
  shows 
  the 
  field 
  within 
  the 
  helix, 
  the 
  second 
  and 
  

   third 
  columns 
  the 
  expansions 
  in 
  millionths 
  of 
  the 
  length 
  of 
  

   core 
  for 
  each 
  helix 
  separately, 
  and 
  the 
  fourth 
  column 
  the 
  corre- 
  

   sponding 
  results 
  when 
  both 
  helices 
  were 
  in 
  circuit. 
  When 
  

   results 
  differed 
  the 
  mean 
  value 
  was 
  taken. 
  Since 
  the 
  motion 
  

   of 
  one 
  fringe 
  across 
  the 
  cross-hairs 
  of 
  the 
  telescope 
  corresponds 
  

   to 
  about 
  30/10 
  6 
  cm 
  (in 
  view 
  of 
  reflection) 
  and 
  since 
  the 
  iron 
  

   cores 
  are 
  about 
  30 
  cm 
  long, 
  the 
  elongation 
  is 
  about 
  10" 
  6 
  per 
  

   fringe. 
  Now 
  the 
  motion 
  of 
  less 
  than 
  one-tenth 
  fringe 
  is 
  

   discernable 
  ; 
  hence 
  an 
  elongation 
  of 
  one 
  ten-millionth 
  is 
  easily 
  

   recognized. 
  

  

  Field 
  

  

  Expansion 
  x 
  

  

  10 
  6 
  . 
  

  

  Remarks. 
  

  

  

  

  

  

  

  dynes/cm 
  2 
  . 
  

  

  Core 
  A. 
  Core 
  B. 
  

  

  Both. 
  

  

  

  

  4 
  

  

  •o 
  o-o 
  

  

  o-o 
  

  

  

  

  1 
  

  

  + 
  •2 
  -0-2 
  

  

  o-o 
  

  

  

  

  11 
  

  

  •3 
  —0-6 
  

  

  0-2 
  

  

  Incipient 
  shifting. 
  

  

  

  14 
  

  

  •6 
  

  

  0-6 
  

  

  0-2 
  

  

  

  

  18 
  

  

  •8 
  

  

  — 
  0-8 
  

  

  ... 
  

  

  

  

  20 
  

  

  •8 
  

  

  — 
  1-0 
  

  

  0-3 
  

  

  

  

  22 
  

  

  ]-2 
  

  

  — 
  1-5 
  

  

  0-4 
  

  

  Continual 
  shifting. 
  

  

  No 
  rotation. 
  

  

  30 
  

  

  1-2 
  

  

  — 
  1-2 
  

  

  

  

  

  44 
  

  

  •1 
  

  

  •5 
  

  

  0'2 
  

  

  Much 
  rotation. 
  

  

  

  100 
  , 
  

  

  

  

  0*5 
  

  

  Rotation. 
  

  

  

  600 
  

  

  ... 
  

  

  ... 
  

  

  _._ 
  

  

  Rotation. 
  

  

  

  * 
  Michelson 
  : 
  1. 
  c, 
  Annex, 
  III. 
  

  

  