﻿of 
  Rigidity 
  in 
  Strong 
  Fields. 
  453 
  

  

  eter, 
  extended 
  downward 
  from 
  the 
  plate. 
  These 
  slits 
  were 
  

   engaged 
  by 
  a 
  cross-wire, 
  2, 
  which 
  passed 
  through 
  the 
  middle 
  of 
  

   the 
  sleeve 
  d, 
  and 
  was 
  soldered 
  to 
  it. 
  It 
  is 
  readily 
  seen 
  that 
  by 
  

   this 
  means 
  any 
  definite 
  amount 
  of 
  twist 
  could 
  be 
  imparted 
  to 
  

   the 
  system 
  of 
  wires 
  at 
  its 
  lower 
  end. 
  Moreover, 
  the 
  cross- 
  

   wire 
  z 
  being 
  free 
  to 
  move 
  up 
  and 
  down 
  the 
  slits 
  in 
  the 
  pillars, 
  

   the 
  tensile 
  strain 
  upon 
  the 
  wires 
  would 
  not 
  be 
  altered 
  by 
  the 
  

   twisting 
  process. 
  

  

  Provision 
  was 
  also 
  made 
  for 
  allowing 
  the 
  wires 
  to 
  take 
  a 
  

   position 
  of 
  zero 
  twist 
  at 
  the 
  beginning 
  of 
  each 
  experiment 
  ; 
  

   for 
  the 
  entire 
  lower 
  part 
  of 
  the 
  apparatus 
  was 
  supported 
  on 
  

   the 
  standard 
  already 
  referred 
  to 
  by 
  means 
  of 
  a 
  clamp, 
  which 
  

   could 
  be 
  raised 
  or 
  lowered 
  by 
  turning 
  a 
  thumb-screw. 
  To 
  

   accomplish 
  this, 
  the 
  lower 
  half 
  of 
  the 
  apparatus 
  was 
  raised 
  by 
  

   means 
  of 
  the 
  screw, 
  until 
  the 
  cross-wire 
  z 
  swung 
  free 
  of 
  the 
  

   slits 
  in 
  the 
  pillars. 
  The 
  system 
  of 
  wires 
  was 
  then 
  free 
  to 
  

   assume 
  its 
  position 
  of 
  zero 
  twist. 
  When 
  they 
  had 
  assumed 
  

   this 
  position, 
  the 
  plate 
  p 
  was 
  turned 
  until 
  the 
  slits 
  in 
  the 
  

   pillars 
  were 
  directly 
  above 
  the 
  cross-wire 
  2, 
  when 
  it 
  was 
  

   clamped 
  and 
  the 
  apparatus 
  lowered 
  into 
  its 
  former 
  position, 
  

   the 
  slits 
  again 
  engaging 
  the 
  cross-wire. 
  The 
  total 
  twist 
  im- 
  

   parted 
  to 
  the 
  system 
  would 
  then 
  be 
  registered 
  as 
  the 
  sum 
  of 
  

   subsequent 
  revolutions 
  of 
  the 
  plates^? 
  and 
  u. 
  

  

  The 
  helix 
  was 
  supported 
  in 
  position 
  on 
  the 
  standard 
  by 
  

   wooden 
  clamps. 
  The 
  standard 
  itself 
  was 
  a 
  vertical 
  frame- 
  work 
  

   of 
  brass 
  piping 
  embedded 
  in 
  a 
  solid 
  cast-iron 
  base 
  mounted 
  on 
  

   bevelling 
  screws, 
  the 
  whole 
  apparatus 
  being 
  located 
  on 
  a 
  pier. 
  

   By 
  suspending 
  the 
  rubber 
  hose 
  connections 
  from 
  the 
  standard 
  

   in 
  loops, 
  the 
  apparatus 
  was 
  rendered 
  free 
  from 
  sensible 
  jarring 
  

   due 
  to 
  the 
  passage 
  of 
  a 
  stream 
  of 
  water 
  under 
  pressure 
  through 
  

   the 
  water-jackets. 
  

  

  For 
  regulating 
  the 
  strength 
  of 
  the 
  current 
  producing 
  the 
  

   field 
  within 
  the 
  helix, 
  a 
  liquid 
  rheostat 
  was 
  used. 
  It 
  was 
  

   found, 
  that, 
  by 
  the 
  use 
  of 
  a 
  rheostat 
  where 
  resistance 
  coils 
  were 
  

   successively 
  thrown 
  into 
  or 
  out 
  of 
  the 
  circuit, 
  the 
  magnetization 
  

   of 
  the 
  wire 
  was 
  hindered 
  as 
  if 
  by 
  mechanical 
  jarring. 
  More- 
  

   over, 
  by 
  the 
  use 
  of 
  a 
  liquid 
  rheostat, 
  much 
  finer 
  gradations 
  of 
  

   the 
  current 
  could 
  be 
  made, 
  — 
  an 
  important 
  requisite 
  in 
  the 
  

   carrying 
  out 
  of 
  the 
  experiments. 
  

  

  In 
  this 
  way, 
  with 
  a 
  maximum 
  E. 
  M. 
  F. 
  of 
  165 
  volts, 
  the 
  cur- 
  

   rent 
  strength 
  was 
  made 
  to 
  vary 
  between 
  and 
  15 
  amperes. 
  

   The 
  corresponding 
  field-strength 
  is 
  obtained 
  by 
  substitut- 
  

   ing 
  the 
  constants 
  given 
  below 
  for 
  the 
  helix 
  in 
  the 
  annexed 
  

   formula. 
  

  

  