﻿450 
  H. 
  D. 
  Day 
  — 
  Magnetic 
  Increment 
  

  

  Hence, 
  if 
  we 
  look 
  up 
  the 
  same 
  torque, 
  t, 
  between 
  two 
  counter- 
  

   twisted 
  wires 
  of 
  the 
  same 
  length, 
  Z, 
  and 
  radius 
  r, 
  On 
  is 
  constant. 
  

   If, 
  therefore, 
  On 
  correspond 
  to 
  the 
  unmagnetic 
  and 
  On" 
  to 
  the 
  

   magnetic 
  wire, 
  

  

  n' 
  — 
  nz=0—B' 
  

  

  or, 
  approximately, 
  — 
  =— 
  -. 
  Tims 
  the 
  relative 
  change 
  of 
  rigid- 
  

   n 
  6 
  

  

  ity 
  due 
  to 
  magnetization 
  is 
  equal 
  to 
  the 
  relative 
  change 
  of 
  

   twist 
  due 
  to 
  the 
  same 
  course. 
  This 
  is, 
  in 
  brief, 
  the 
  method 
  

   pursued 
  in 
  the 
  following 
  work. 
  Apart 
  from 
  the 
  inherent 
  and 
  

   unavoidable 
  irregularities 
  in 
  the 
  torsional 
  resilience 
  and 
  vis- 
  

   cosity 
  of 
  iron, 
  the 
  method 
  unfortunately 
  involves 
  the 
  fourth 
  

   power 
  of 
  the 
  radius. 
  It 
  has 
  the 
  advantage 
  of 
  a 
  differential 
  

   method, 
  however, 
  as 
  well 
  as 
  others 
  which 
  appear 
  in 
  the 
  follow- 
  

   ing 
  description. 
  

  

  Pure 
  iron 
  wires 
  were 
  first 
  prepared 
  by 
  drawing 
  through 
  

   steel 
  plates. 
  These 
  wires, 
  although 
  not 
  as 
  perfect 
  as 
  could 
  be 
  

   desired 
  for 
  observations 
  by 
  this 
  method, 
  were 
  free 
  from 
  all 
  but 
  

   microscopic 
  imperfections. 
  They 
  were 
  thoroughly 
  annealed 
  

   and 
  straightened 
  by 
  being 
  suspended 
  vertically 
  in 
  a 
  glass 
  tube 
  

   filled 
  with 
  dry 
  hydrogen 
  and 
  then 
  being 
  heated 
  to 
  a 
  cherry 
  

   red 
  by 
  the 
  passage 
  of 
  an 
  electric 
  current 
  through 
  them. 
  In 
  

   this 
  way, 
  bright, 
  smooth 
  wires 
  free 
  from 
  corrosion 
  were 
  

   obtained. 
  

  

  A 
  preliminary 
  trial 
  of 
  the 
  largest 
  size 
  of 
  wires 
  was 
  made 
  in 
  

   a 
  simple 
  form 
  of 
  the 
  apparatus 
  used. 
  It 
  was 
  then 
  found, 
  that, 
  

   along 
  with 
  the 
  effect 
  of 
  magnetization 
  on 
  the 
  rigidity 
  of 
  the 
  

   wire, 
  were 
  involved 
  other 
  effects 
  upon 
  its 
  rigidity 
  due 
  to 
  other 
  

   causes. 
  The 
  magnetizing 
  coil 
  became 
  much 
  heated 
  and 
  the 
  

   effect 
  of 
  its 
  rise 
  in 
  temperature 
  upon 
  the 
  rigidity 
  of 
  the 
  

   enclosed 
  wire 
  was 
  clearly 
  apparent. 
  A 
  group 
  of 
  curves 
  plotted 
  

   from 
  data 
  obtained 
  by 
  uniting 
  the 
  effects 
  of 
  temperature 
  and 
  

   magnetization 
  and 
  again 
  by 
  separating 
  the 
  two, 
  the 
  field 
  being 
  

   kept 
  constant, 
  showed 
  that 
  the 
  increment 
  of 
  rigidity 
  due 
  to 
  the 
  

   rise 
  in 
  temperature 
  was 
  of 
  the 
  opposite 
  sign 
  to 
  that 
  due 
  to 
  

   magnetization, 
  namely, 
  negative, 
  and 
  nearly 
  proportional 
  to 
  

   the 
  increase 
  of 
  temperature. 
  This 
  heat-effect 
  was 
  almost 
  

   entirely 
  removed 
  by 
  winding 
  the 
  helix 
  about 
  a 
  water-jacket, 
  

   through 
  which 
  a 
  stream 
  of 
  cold 
  water 
  was 
  kept 
  constantly 
  

   flowing 
  and 
  within 
  which 
  was 
  the 
  wire 
  to 
  be 
  magnetized. 
  

   Later, 
  the 
  other 
  wire 
  also 
  was 
  surrounded 
  by 
  a 
  similar 
  water- 
  

   jacket 
  through 
  which 
  the 
  same 
  stream 
  of 
  water 
  was 
  made 
  to 
  

   pass. 
  The 
  two 
  wires 
  were 
  thus 
  kept 
  at 
  the 
  same 
  uniform 
  tern- 
  

  

  