﻿of 
  Rigidity 
  in 
  Strong 
  Fields. 
  

  

  451 
  

  

  perature, 
  a 
  necessary 
  precaution 
  owing 
  to 
  the 
  delicacy 
  of 
  the 
  

   differential 
  method 
  employed. 
  Again, 
  variations 
  in 
  the 
  tensile 
  

   strain 
  of 
  the 
  wires 
  were 
  found 
  

   to 
  produce 
  a 
  noticeable 
  effect 
  

   upon 
  the 
  data 
  obtained. 
  This 
  

   source 
  of 
  error 
  was 
  removed 
  by 
  

   giving 
  the 
  lower 
  end 
  of 
  the 
  sys- 
  

   tem 
  of 
  wires 
  vertical 
  freedom 
  of 
  

   motion, 
  and 
  suspending 
  there- 
  

   from 
  a 
  small 
  bucket 
  of 
  mercury, 
  

   the 
  weight 
  of 
  which 
  was 
  made 
  

   proportional 
  to 
  the 
  cross-sections 
  

   of 
  the 
  wires, 
  whenever 
  wires 
  of 
  

   different 
  diameters 
  were 
  inserted 
  

   in 
  the 
  apparatus. 
  

  

  The 
  method 
  of 
  observation 
  is 
  

   made 
  clear 
  by 
  the 
  section 
  draw- 
  

   ing 
  of 
  the 
  perfected 
  apparatus 
  

   given 
  in 
  fig. 
  1. 
  A 
  vertical 
  sys- 
  

   tem 
  of 
  two 
  iron 
  wires 
  have 
  their 
  

   adjoining 
  ends 
  soldered 
  between 
  

   two 
  straight 
  adjacent 
  pieces 
  of 
  

   brass 
  wire 
  about 
  4 
  cm 
  long. 
  These 
  

   brass 
  wires, 
  besides 
  forming 
  a 
  

   rigid 
  connection 
  between 
  the 
  

   two 
  iron 
  wires, 
  serve 
  also 
  to 
  sup- 
  

   port 
  a 
  \ 
  " 
  circular 
  mirror, 
  g, 
  and 
  a 
  

   pair 
  of 
  vanes, 
  r, 
  r, 
  of 
  copper 
  

   foil, 
  which 
  are 
  soldered 
  to 
  the 
  

   ends 
  of 
  a 
  bent 
  cross-piece 
  of 
  fine 
  

   brass 
  wire, 
  so 
  as 
  to 
  hang 
  verti- 
  

   cally 
  in 
  a 
  circular 
  water-bath, 
  o, 
  

   which, 
  by 
  means 
  of 
  a 
  central 
  

   piece 
  of 
  tubing 
  slips 
  upon 
  and 
  is 
  

   supported 
  by 
  the 
  water-jacket^, 
  

   which 
  envelops 
  the 
  lower 
  wire, 
  

   Z>. 
  A 
  small 
  spring 
  collar, 
  w, 
  

   holds 
  the 
  bath 
  at 
  the 
  proper 
  

   position 
  on 
  the 
  water-jacket. 
  

   These 
  vanes 
  serve 
  to 
  damp 
  the 
  

   vibrations 
  of 
  the 
  wires. 
  

  

  The 
  upper 
  end 
  of 
  the 
  upper 
  

   iron 
  wire 
  is 
  soldered 
  to 
  a 
  short 
  

   piece 
  of 
  brass 
  rod, 
  e, 
  which 
  is 
  

   made 
  to 
  screw 
  tightly 
  into 
  the 
  

   end 
  of 
  a 
  vertical 
  shaft, 
  A, 
  which 
  is 
  free 
  to 
  revolve 
  within 
  the 
  

   sleeve, 
  fa 
  This 
  sleeve 
  is 
  grasped 
  in 
  the 
  jaws 
  of 
  a 
  clamp, 
  which 
  

  

  