﻿Williams 
  — 
  Twist 
  in 
  Steel 
  and 
  Nickel 
  Hods. 
  561 
  

  

  A 
  sample 
  of 
  the 
  rod 
  was 
  placed 
  in 
  dilute 
  nitric 
  acid 
  and 
  after 
  

   dissolving 
  for 
  a 
  little 
  while 
  spiral 
  ridges 
  were 
  plainly 
  to 
  be 
  

   seen 
  running 
  around 
  the 
  samples. 
  This 
  showed 
  that 
  the 
  rods 
  

   were 
  not 
  homogeneous 
  but 
  in 
  the 
  process 
  of 
  forming 
  had 
  been 
  

   given 
  a 
  definite 
  helical 
  structure. 
  We 
  know 
  that 
  magnetism 
  

   produces 
  mechanical 
  strains 
  in 
  ferromagnetic 
  substances 
  and 
  

   also 
  that 
  mechanical 
  stresses 
  produce 
  changes 
  in 
  magnetic 
  prop- 
  

   erties. 
  Hence 
  we 
  may 
  expect 
  that 
  in 
  the 
  case 
  of 
  the 
  rods 
  

   having 
  a 
  definite 
  mechanical 
  structure, 
  as 
  these 
  nickel 
  rods 
  do, 
  

   a 
  large 
  number 
  of 
  the 
  elementary 
  magnets 
  would 
  have 
  a 
  

   definite 
  orientation. 
  This 
  may 
  help 
  to 
  increase 
  the 
  permanent 
  

   magnetism 
  observed 
  in 
  these 
  rods. 
  

  

  Again, 
  if 
  these 
  elementary 
  magnets 
  are 
  elongated 
  as 
  has 
  

   been 
  suggested 
  and 
  swing 
  from 
  one 
  position 
  of 
  equilibrium 
  to 
  

   another, 
  then 
  in 
  their 
  swinging 
  they 
  would 
  produce 
  changes 
  in 
  

   length 
  along 
  the 
  spiral 
  formation 
  of 
  the 
  rod 
  and 
  consequently 
  

   a 
  twisting 
  due 
  to 
  a 
  longitudinal 
  held. 
  This 
  is 
  in 
  agreement 
  

   with 
  the 
  original 
  observation 
  of 
  Wiedemann, 
  who 
  found 
  that 
  

   reversing 
  the 
  direction 
  of 
  the 
  magnetic 
  held 
  did 
  not 
  reverse 
  

   the 
  direction 
  of 
  twist 
  in 
  rods 
  having 
  permanent 
  torsional 
  set, 
  

   that 
  is, 
  a 
  change 
  in 
  length 
  along 
  the 
  helix, 
  whether 
  it 
  is 
  due 
  to 
  

   an 
  up 
  or 
  a 
  down 
  field, 
  produces 
  the 
  same 
  sort 
  of 
  a 
  twist. 
  

   The 
  conditions, 
  therefore, 
  for 
  a 
  twist 
  due 
  to 
  a 
  longitudinal 
  

   magnetic 
  field 
  seem 
  to 
  be 
  (1) 
  the 
  presence 
  of 
  a 
  permanent 
  tor- 
  

   sional 
  set, 
  either 
  produced 
  at 
  the 
  time 
  the 
  rod 
  was 
  drawn 
  or 
  

   rolled 
  or 
  else 
  produced 
  by 
  the 
  experimenter 
  as 
  Weidemann 
  

   and 
  Smith 
  did 
  in 
  their 
  work; 
  or 
  (2) 
  the 
  elementary 
  magnets 
  

   may 
  be 
  swung 
  into 
  spiral 
  formations 
  by 
  magnetic 
  processes. 
  

  

  In 
  testing 
  about 
  fifteen 
  steel 
  rods 
  for 
  the 
  effect 
  here 
  studied 
  

   it 
  was 
  quite 
  evident 
  that 
  in 
  some 
  the 
  twist 
  was 
  largely 
  due 
  to 
  

   a 
  definite 
  setting 
  of 
  the 
  elementary 
  magnets 
  along 
  helical 
  lines 
  

   in 
  the 
  rod. 
  This 
  is 
  further 
  corroborated 
  by 
  the 
  fact 
  that 
  

   increased 
  permanent 
  magnetization 
  increased 
  the 
  effect. 
  The 
  

   initial 
  and 
  final 
  twists 
  for 
  the 
  nickel 
  rods 
  are 
  in 
  a 
  direction 
  to 
  

   increase 
  still 
  more 
  the 
  permanent 
  torsional 
  set. 
  

  

  These 
  results 
  show 
  that 
  for 
  some 
  specimens 
  of 
  ferromagnetic 
  

   substances 
  two 
  mechanical 
  effects 
  may 
  occur 
  when 
  a 
  longitudi- 
  

   nal 
  magnetic 
  field 
  is 
  imposed 
  upon 
  them, 
  viz., 
  a 
  change 
  in 
  

   length 
  and 
  a 
  twist. 
  These 
  effects 
  and 
  also 
  other 
  magneto- 
  

   strictive 
  effects 
  are 
  larger 
  in 
  nickel 
  than 
  in 
  iron 
  or 
  steel. 
  The 
  

   twist 
  for 
  steel 
  was 
  so 
  small 
  that 
  it 
  was 
  not 
  plotted. 
  The 
  maxi- 
  

   mum 
  twist 
  shown 
  in 
  fig. 
  2, 
  film 
  T 
  4 
  and 
  T 
  5 
  , 
  amounted 
  to 
  about 
  

   100 
  seconds 
  of 
  arc. 
  Following 
  each 
  graph 
  for 
  both 
  the 
  nickel 
  

   and 
  steel 
  rods, 
  the 
  spot 
  of 
  light 
  was 
  allowed 
  to 
  record 
  the 
  posi- 
  

   tion 
  of 
  deflection 
  when 
  the 
  field 
  was 
  thrown 
  off. 
  This 
  helps 
  

   to 
  make 
  the 
  twist 
  in 
  the 
  steel 
  rod 
  more 
  apparent. 
  The 
  twists 
  

   observed 
  in 
  the 
  nickel 
  rods 
  are, 
  as 
  has 
  been 
  said, 
  apparently 
  

  

  