﻿116 
  Barus 
  — 
  Trial 
  of 
  Interferential 
  Induction 
  balance. 
  

  

  smaller 
  self-induction, 
  retaining 
  the 
  condition 
  of 
  identity. 
  

   Thus 
  if 
  only 
  a 
  single 
  layer 
  of 
  wire 
  is 
  used 
  on 
  the 
  above 
  frame, 
  

   and 
  if 
  the 
  core 
  of 
  half 
  the 
  above 
  diameter 
  (made 
  tubular 
  or 
  

   cross-shaped 
  in 
  section) 
  be 
  inserted, 
  the 
  self-induction 
  will 
  be 
  

   reduced 
  to 
  *002 
  henrys, 
  and 
  the 
  impedance 
  for 
  10,000 
  vibra- 
  

   tions 
  to 
  126 
  ohms. 
  The 
  field 
  of 
  this 
  helix 
  is 
  14 
  dynes 
  per 
  

   ampere, 
  and 
  since 
  half 
  this 
  value 
  is 
  just 
  sufficient 
  to 
  elongate 
  

   the 
  cores 
  appreciably, 
  about 
  90 
  volts 
  would 
  be 
  needed 
  to 
  pro- 
  

   duce 
  the 
  vibration, 
  apart 
  from 
  the 
  favorable 
  condition 
  of 
  reso- 
  

   nance. 
  Finally, 
  in 
  view 
  of 
  the 
  large 
  factor 
  R/ 
  L 
  — 
  750, 
  after 
  

   0*0001 
  second 
  the 
  extra 
  current 
  has 
  kept 
  the 
  current 
  strength 
  

   reduced 
  to 
  about 
  1 
  per 
  cent 
  of 
  the 
  maximum 
  value. 
  Hence 
  

   the 
  current 
  must 
  be 
  100 
  times 
  stronger 
  than 
  when 
  it 
  acts 
  con- 
  

   tinuously, 
  R/L 
  — 
  750, 
  requiring 
  70 
  volts 
  to 
  maintain 
  it. 
  

  

  To 
  summarize 
  : 
  Setting 
  considerations 
  of 
  mechanism 
  aside, 
  

   an 
  arrangement 
  of 
  the 
  kind 
  shown 
  above 
  supplied 
  with 
  about 
  

   100 
  volts 
  ought 
  to 
  indicate 
  the 
  retardation 
  along 
  something 
  

   over 
  a 
  single 
  knot 
  of 
  wire 
  of 
  the 
  high 
  capacity 
  stated, 
  inserted 
  

   between 
  the 
  helices. 
  This 
  retardation 
  will 
  be 
  exhibited 
  by 
  the 
  

   passage 
  of 
  one 
  yellow 
  interference 
  fringe 
  across 
  the 
  cross- 
  hairs 
  

   of 
  the 
  telescope. 
  

  

  Brown 
  University, 
  Providence, 
  R. 
  I. 
  

  

  

  