﻿476 
  

  

  Presents. 
  

  

  [May 
  13, 
  

  

  experiments 
  made 
  to-day 
  for 
  the 
  purpose 
  of 
  finding 
  accurately 
  the 
  amount 
  

   of 
  the 
  negative 
  current 
  which, 
  by 
  neutralizing 
  the 
  vertical 
  force 
  of 
  the 
  

   earth 
  or 
  the 
  wire, 
  gives 
  an 
  accurate 
  zero 
  effect 
  for 
  the 
  " 
  off 
  " 
  and 
  " 
  on/' 
  

   The 
  dotted 
  prolongation 
  of 
  the 
  curve 
  through 
  the 
  plus's, 
  to 
  cut 
  the 
  line 
  

   of 
  abscissas 
  on 
  its 
  negative 
  side, 
  is 
  ideal, 
  and 
  is 
  inserted 
  to 
  illustrate 
  the 
  

   relation 
  of 
  this 
  curve 
  to 
  the 
  other. 
  By 
  the 
  two 
  curves 
  cutting 
  the 
  line 
  

   of 
  abscissas 
  at 
  +8 
  and 
  —8, 
  we 
  see 
  that 
  8 
  is 
  the 
  strength 
  of 
  the 
  current, 
  

   measured 
  on 
  the 
  scale 
  of 
  the 
  battery-galvanometer, 
  which 
  gives 
  a 
  magnetic 
  

   force 
  in 
  the 
  axis 
  of 
  the 
  helix 
  equal 
  to 
  the 
  vertical 
  component 
  of 
  the 
  ter- 
  

   restrial 
  magnetic 
  force. 
  

  

  7. 
  Next 
  a 
  series 
  of 
  experiments 
  to 
  test 
  the 
  inductive 
  effects 
  of 
  

   repeatedly 
  making 
  the 
  current 
  always 
  in 
  one 
  direction, 
  and 
  stopping 
  it, 
  

   with 
  the 
  weight 
  of 
  14 
  lbs. 
  always 
  on, 
  and 
  again 
  with 
  the 
  weight 
  off, 
  and 
  

   this 
  with 
  various 
  degrees 
  of 
  current, 
  feebler 
  than 
  those 
  used 
  in 
  the 
  earlier 
  

   experiments. 
  The 
  results 
  with 
  all 
  the 
  different 
  intensities 
  of 
  magnetizing 
  

   force 
  thus 
  applied 
  were 
  the 
  same 
  in 
  kind 
  as 
  that 
  which 
  I 
  found 
  on 
  the 
  

   23rd 
  of 
  December, 
  operating 
  with 
  a 
  much 
  stronger 
  magnetizing 
  force 
  on 
  

   the 
  first 
  soft-iron 
  wire 
  tried 
  ; 
  that 
  is 
  to 
  say 
  (contrarily 
  to 
  what 
  I 
  had 
  found 
  

   in 
  the 
  steel 
  wires), 
  the 
  change 
  of 
  magnetization 
  produced 
  by 
  repeated 
  appli- 
  

   cations 
  and 
  annidlings 
  of 
  the 
  magnetizing 
  force 
  of 
  the 
  helix 
  ivas 
  greater 
  with 
  

   the 
  weight 
  off 
  than 
  on. 
  

  

  [Note 
  on 
  Diagram, 
  added 
  July 
  2, 
  1875. 
  — 
  A 
  continuation 
  of 
  the 
  experi- 
  

   ments 
  with 
  higher 
  and 
  higher 
  magnetiziug 
  powers, 
  since 
  the 
  communica- 
  

   tion 
  of 
  this 
  paper, 
  disproves 
  the 
  negative 
  minimum 
  indicated 
  by 
  the 
  

   curves 
  on 
  the 
  diagram, 
  and 
  proves 
  an 
  asymptotic 
  approach 
  to 
  a 
  value 
  

   approximately 
  — 
  12, 
  of 
  ordinates, 
  for 
  infinitely 
  great 
  positive 
  values 
  of 
  

   the 
  abscissas.] 
  

  

  Presents 
  received, 
  May 
  13, 
  1875. 
  

  

  Transactions. 
  

  

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