﻿1875.] 
  On 
  the 
  Electro 
  dynamic 
  Qualities 
  of 
  Metals. 
  

  

  445 
  

  

  Y. 
  " 
  Electrodynamic 
  Qualities 
  of 
  Metals. 
  (Continued 
  from 
  Phil. 
  

   Trans, 
  for 
  February 
  28, 
  1856.)— 
  Part 
  VI. 
  Effects 
  of 
  Stress 
  

   on 
  Magnetization." 
  By 
  Prof. 
  Sir 
  W. 
  Thomson, 
  LL.D., 
  

   E.R.S. 
  Received 
  May 
  27, 
  1875. 
  

  

  (Abstract.) 
  

  

  "Weber's 
  method, 
  by 
  aid 
  of 
  electromagnetic 
  induction 
  and 
  a 
  " 
  ballistic 
  

   galvanometer" 
  to 
  measure 
  it, 
  which 
  has 
  been 
  practised 
  with 
  so 
  much 
  

   success 
  by 
  Thalen, 
  Roland, 
  and 
  others, 
  has 
  been 
  used 
  in 
  the 
  investigation 
  

   of 
  which 
  the 
  results 
  are 
  at 
  present 
  communicated 
  ; 
  but 
  partial 
  trials 
  have 
  

   been 
  made 
  by 
  the 
  direct 
  magnetometric 
  method 
  (deflections 
  of 
  a 
  needle), 
  

   and 
  this 
  method 
  is 
  kept 
  in 
  view 
  for 
  testing 
  slow 
  changes 
  of 
  magnetiza- 
  

   tion 
  which 
  the 
  electromagnetic 
  method 
  fails 
  to 
  detect. 
  

  

  The 
  metals 
  experimented 
  on 
  have 
  been 
  steel 
  pianoforte- 
  wire, 
  of 
  the 
  

   kind 
  used 
  for 
  deep-sea 
  soundings 
  by 
  the 
  American 
  Navy 
  and 
  British 
  

   cable-ships 
  ; 
  and 
  soft-iron 
  wires 
  of 
  about 
  the 
  same 
  gauge, 
  but 
  of 
  several 
  

   different 
  qualities. 
  

  

  I. 
  Steel. 
  

  

  The 
  steel 
  wire 
  weighs 
  about 
  14| 
  lbs. 
  per 
  nautical 
  mile 
  and 
  bears 
  

   230 
  lbs. 
  "Weights 
  of 
  from 
  28 
  lbs. 
  to 
  112 
  lbs. 
  were 
  hung 
  on 
  it 
  and 
  taken 
  

   off, 
  and 
  results 
  described 
  shortly 
  as 
  follows 
  were 
  found 
  : 
  — 
  

  

  (1) 
  The 
  magnetization 
  is 
  diminished 
  by 
  hanging 
  on 
  weights, 
  and 
  

   increased 
  by 
  taking 
  the 
  weights 
  off, 
  when 
  the 
  magnetizing 
  current 
  is 
  kept 
  

   flowing. 
  

  

  (2) 
  The 
  residual 
  magnetism 
  remaining 
  after 
  the 
  current 
  is 
  stopped 
  is 
  

   also 
  diminished 
  by 
  hanging 
  on 
  the 
  weights, 
  and 
  increased 
  by 
  taking 
  

   them 
  off. 
  

  

  (3) 
  The 
  absolute 
  amount 
  of 
  the 
  difference 
  of 
  magnetization 
  produced 
  

   by 
  putting 
  on 
  and 
  taking 
  off 
  weights 
  is 
  greater 
  with 
  the 
  mere 
  residual 
  mag- 
  

   netism 
  when 
  the 
  current 
  is 
  stopped 
  than 
  with 
  the 
  whole 
  magnetism 
  when 
  

   the 
  magnetizing 
  current 
  is 
  kept 
  flowing. 
  

  

  (4) 
  The 
  change 
  of 
  magnetization 
  produced 
  by 
  making 
  the 
  magnetizing 
  

   current 
  always 
  in 
  one 
  direction 
  and 
  stopping 
  it 
  is 
  greater 
  with 
  the 
  weights 
  

   on 
  than 
  off. 
  

  

  (5) 
  After 
  the 
  magnetizing 
  current 
  has 
  been 
  made 
  in 
  either 
  direction 
  

   and 
  stopped, 
  the 
  effect 
  of 
  making 
  it 
  in 
  the 
  reverse 
  direction 
  is 
  less 
  with 
  

   the 
  weights 
  on 
  than 
  off. 
  

  

  (6) 
  The 
  difference 
  announced 
  in 
  (5) 
  is 
  a 
  much 
  greater 
  difference 
  than 
  

   that 
  in 
  the 
  opposite 
  direction 
  between 
  the 
  effects 
  of 
  stopping 
  the 
  current 
  

   with 
  weights 
  on 
  and 
  weights 
  off, 
  announced 
  in 
  (4). 
  

  

  (7) 
  When 
  the 
  current 
  is 
  suddenly 
  reversed, 
  the 
  magnetic 
  effect 
  is 
  less 
  

   with 
  the 
  weights 
  on 
  than 
  with 
  the 
  weights 
  off. 
  

  

  