﻿352 
  

  

  Prof. 
  A. 
  Anderson 
  on 
  Electric 
  

  

  produced 
  by 
  very 
  small 
  potential 
  differences 
  and 
  increase 
  

   with 
  the 
  applied" 
  voltage, 
  for 
  pressures 
  up 
  to 
  about 
  80 
  volts, 
  

   approximately 
  according 
  to 
  Ohm's 
  law, 
  after 
  which 
  the 
  

   increase 
  of 
  current 
  is 
  much 
  more 
  rapid 
  than 
  the 
  increase 
  

   of 
  voltage. 
  

  

  The 
  questions 
  arise— 
  why 
  does 
  a 
  current 
  pass 
  ? 
  and 
  what 
  

   carries 
  it 
  ? 
  To 
  say 
  that 
  there 
  is 
  metallic 
  contact 
  produced 
  

   by 
  the 
  electrostatic 
  pressure 
  between 
  the 
  plates 
  will 
  not 
  

   solve 
  the 
  difficulty, 
  at 
  any 
  rate 
  in 
  the 
  case 
  where 
  the 
  metals 
  

   are 
  different 
  and 
  no 
  potential 
  applied. 
  When 
  the 
  metals 
  are 
  

   the 
  same 
  and 
  a 
  potential 
  applied, 
  experiment 
  shows 
  that 
  the 
  

   current 
  diminishes 
  when 
  the 
  pressure 
  of 
  the 
  air 
  is 
  diminished, 
  

   and, 
  if 
  the 
  pressure 
  is 
  not 
  made 
  too 
  small, 
  and 
  the 
  air 
  in 
  the 
  

   copper 
  box 
  not 
  kept 
  at 
  the 
  low 
  pressure 
  too 
  long, 
  again 
  

   increases 
  as 
  the 
  pressure 
  is 
  increased, 
  the 
  current, 
  however, 
  

   for 
  the 
  same 
  pressure 
  being 
  somewhat 
  smaller 
  when 
  the 
  

   pressure 
  is 
  being 
  increased 
  than 
  when 
  it 
  is 
  being 
  decreased. 
  

   This 
  is 
  shown 
  in 
  fig. 
  2 
  for 
  an 
  applied 
  difference 
  of 
  potential 
  

  

  Fig. 
  2. 
  

  

  k 
  

  

  1 
  

  

  

  

  

  

  

  

  

  

  

  

  

  \ 
  

  

  i 
  

  

  

  1 
  

  

  

  

  

  

  

  

  

  

  

  

  

  / 
  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  > 
  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  ^>f 
  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  . 
  

  

  

  

  

  J^ 
  

  

  

  

  

  

  

  

  

  

  

  

  1 
  

  

  

  

  -^" 
  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  ^^ 
  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  30 
  35 
  4-0 
  45 
  50 
  55 
  

  

  Pressure 
  in 
  cms 
  ofmegury. 
  

  

  of 
  100 
  volts. 
  Here 
  the 
  pressure 
  was 
  diminished 
  to 
  that 
  

   equivalent 
  to 
  8 
  millimetres 
  of 
  mercury. 
  

  

  This 
  dependence 
  of 
  the 
  current 
  on 
  the 
  pressure 
  of 
  the 
  air 
  

  

  