﻿A 
  New 
  Harmonic 
  Analyser. 
  85 
  

  

  almost 
  neutralized 
  the 
  self-inductance, 
  which 
  was 
  one 
  henry 
  

   for 
  each 
  coil, 
  or 
  four 
  henrys 
  for 
  them 
  in 
  series. 
  

  

  Altogether 
  the 
  results 
  of 
  experiment 
  justify 
  me 
  in 
  claiming 
  

   that 
  these 
  methods 
  will 
  take 
  a 
  prominent 
  place 
  in 
  electrical 
  

   measurement, 
  especially 
  where 
  fluid 
  resistances, 
  inductances, 
  

   and 
  capacities 
  are 
  to 
  be 
  measured. 
  They 
  also 
  seem 
  to 
  me 
  to 
  

   settle 
  the 
  question 
  as 
  to 
  standard 
  inductances 
  or 
  capacities, 
  

   as 
  inductances 
  have 
  a 
  real 
  constant 
  which 
  can 
  now 
  be 
  com- 
  

   pared 
  to 
  1 
  in 
  10,000 
  at 
  least. 
  

  

  It 
  is 
  to 
  be 
  noted 
  that 
  all 
  the 
  methods 
  15 
  to 
  24 
  can 
  be 
  

   modified 
  by 
  passing 
  the 
  main 
  current 
  through 
  one 
  coil 
  of 
  the 
  

   electrodynamometer 
  and 
  the 
  branch 
  current 
  through 
  the 
  other. 
  

   The 
  deflexion 
  will 
  then 
  be 
  zero 
  for 
  a 
  more 
  complicated 
  re- 
  

   lation 
  than 
  the 
  ones 
  given. 
  If, 
  however, 
  one 
  adjustment 
  is 
  

   known 
  and 
  made, 
  the 
  method 
  gives 
  the 
  other 
  equation. 
  

  

  Thus 
  method 
  18 
  requires 
  R 
  y 
  R" 
  — 
  R'R 
  y/ 
  = 
  0. 
  Hence, 
  when 
  

   this 
  is 
  satisfied 
  we 
  must 
  have 
  the 
  other 
  condition 
  alone 
  to 
  be 
  

   satisfied. 
  Also 
  in 
  method 
  22, 
  when 
  we 
  know 
  the 
  ratio 
  of 
  

   the 
  self 
  and 
  mutual 
  inductances 
  in 
  the 
  coil, 
  the 
  resistances 
  

   can 
  be 
  adjusted 
  to 
  satisfy 
  one 
  equation, 
  while 
  the 
  experiment 
  

   will 
  give 
  the 
  other, 
  and 
  hence 
  the 
  capacity 
  in 
  terms 
  of 
  the 
  

   inductance. 
  Again, 
  pass 
  a 
  current 
  whose 
  phase 
  can 
  be 
  varied 
  

   through 
  one 
  coil 
  of 
  the 
  electrodynamometer, 
  and 
  connect 
  the 
  

   circuit 
  to 
  be 
  tested 
  through 
  the 
  other. 
  Vary 
  the 
  adjustments 
  

   of 
  resistances 
  until 
  the 
  deflexion 
  is 
  zero, 
  however 
  the 
  phase 
  

   of 
  current 
  through 
  the 
  first 
  coil 
  may 
  be 
  varied. 
  

  

  The 
  best 
  methods 
  to 
  apply 
  the 
  first 
  modification 
  to 
  are 
  

   15 
  a, 
  16 
  a 
  and 
  b, 
  18, 
  20, 
  21, 
  22, 
  and 
  24. 
  In 
  these 
  either 
  a 
  

   Wheatstone 
  bridge 
  can 
  be 
  adjusted 
  or 
  the 
  ratio 
  of 
  the 
  self 
  

   and 
  mutual 
  inductances 
  in 
  a 
  given 
  coil 
  can 
  be 
  assumed 
  

   known 
  and 
  the 
  resistance 
  adjusted 
  thereby. 
  

  

  The 
  value 
  of 
  this 
  addition 
  is 
  in 
  the 
  increased 
  accuracy 
  and 
  

   sensitiveness 
  of 
  the 
  method, 
  an 
  increase 
  of 
  more 
  than 
  one 
  

   hundredfold 
  being 
  assured. 
  

  

  As 
  a 
  standard 
  I 
  recommend 
  two 
  or 
  three 
  coils 
  laid 
  together 
  

   with 
  their 
  inductances 
  determined, 
  and 
  not 
  a 
  condenser, 
  even 
  

   an 
  air 
  condenser. 
  

  

  YI. 
  A 
  New 
  Harmonic 
  Analyser. 
  

   By 
  A. 
  A. 
  Michelson 
  and 
  S. 
  W. 
  Stratton*. 
  

  

  [Plates 
  XI.-XVIIL] 
  

  

  EVERYONE 
  who 
  has 
  had 
  occasion 
  to 
  calculate 
  or 
  to 
  con- 
  

   struct 
  graphically 
  the 
  resultant 
  of 
  a 
  large 
  number 
  of 
  

   simple 
  harmonic 
  motions, 
  has 
  felt 
  the 
  need 
  of 
  some 
  simple 
  

   * 
  Communicated 
  by 
  the 
  Authors. 
  

  

  \ 
  

  

  