﻿88 
  

  

  Prof. 
  L. 
  R. 
  Ingersoll 
  on 
  Magnetic 
  

  

  one 
  furnishing 
  a 
  high 
  voltage 
  and 
  small 
  current 
  — 
  it 
  was 
  

   almost 
  impossible 
  to 
  avoid 
  a 
  certain 
  amount 
  of 
  oxidation. 
  

   This 
  gave 
  place 
  to 
  a 
  smaller 
  coil, 
  furnishing 
  a 
  larger 
  current 
  

   and 
  taking 
  a 
  much 
  shorter 
  time 
  — 
  half 
  an 
  hour 
  or 
  less 
  — 
  to 
  

   deposit 
  a 
  film. 
  Still 
  later 
  a 
  2000 
  volt 
  generator 
  set 
  was 
  used, 
  

   but 
  most 
  of 
  the 
  films 
  discussed 
  in 
  the 
  present 
  paper 
  were 
  

   deposited 
  with 
  the 
  smaller 
  induction-coil. 
  

  

  Oxidation, 
  when 
  present, 
  was 
  readily 
  detected 
  by 
  the 
  

   brownish 
  colour 
  imparted 
  to 
  the 
  film. 
  It 
  was 
  doubtless 
  caused 
  

   by 
  the 
  minute 
  quantity 
  of 
  occluded 
  air 
  which 
  would 
  still 
  

   remain 
  even 
  after 
  repeated 
  washings 
  with 
  hydrogen. 
  When, 
  

   however, 
  the 
  greatest 
  care 
  was 
  taken 
  in 
  getting 
  rid 
  of 
  this 
  

   remaining 
  air 
  by 
  frequent 
  washings 
  with 
  dry 
  hydrogen, 
  

   between 
  short 
  periods 
  of 
  electrical 
  discharge, 
  films 
  were 
  

   obtained 
  which 
  were 
  quite 
  colourless, 
  of 
  a 
  greyish 
  appearance 
  

   when 
  thin, 
  and 
  looking 
  like 
  smoked 
  glass 
  when 
  thick. 
  This 
  

   accords 
  with 
  the 
  description 
  of 
  Houllevigue 
  * 
  of 
  the 
  appear- 
  

   ance 
  of 
  iron 
  films 
  free 
  of 
  oxidation. 
  The 
  films 
  were 
  kept 
  in 
  

   an 
  atmosphere 
  of 
  dry 
  hydrogen 
  when 
  not 
  being 
  used, 
  and 
  did 
  

   not 
  deteriorate 
  appreciably 
  for 
  many 
  weeks. 
  When 
  left 
  for 
  

   some 
  time 
  in 
  moist 
  air 
  they 
  slowly 
  oxidized 
  to 
  a 
  yellow 
  

   colour. 
  

  

  Measurements. 
  — 
  About 
  forty 
  films 
  were 
  deposited 
  in 
  all, 
  

   in 
  lots 
  of 
  two 
  or 
  three 
  at 
  a 
  time 
  usually, 
  and 
  perhaps 
  half 
  

   of 
  these 
  tested. 
  Out 
  of 
  this 
  number 
  four 
  have 
  been 
  selected 
  

   which 
  had 
  suitably 
  varying 
  thicknesses 
  and 
  which 
  show^ed 
  

   almost 
  no 
  traces 
  of 
  oxidation 
  ; 
  and 
  the 
  curves 
  made 
  from 
  

   these 
  are 
  shown 
  in 
  PL 
  I. 
  figs. 
  6-9. 
  

  

  Fig. 
  5. 
  

  

  The 
  rotations 
  shown 
  in 
  the 
  " 
  transmission 
  ^' 
  curve 
  were 
  

   measured 
  with 
  the 
  film 
  in 
  position 
  A, 
  fig. 
  5, 
  the 
  pole-pieces 
  

   * 
  Jour. 
  d. 
  Phys. 
  (4) 
  iv. 
  p. 
  406 
  (1905). 
  

  

  