﻿230 
  Messrs. 
  Pollock, 
  Kanclaud, 
  and 
  Norman 
  on 
  the 
  

  

  collision 
  with 
  the 
  gas 
  molecules, 
  the 
  electric 
  force 
  may 
  

   change 
  sign 
  in 
  the 
  near 
  neighbourhood 
  of 
  the 
  heated 
  surface. 
  

   In 
  this 
  case 
  the 
  potential-difference 
  between 
  the 
  electrodes 
  

   for 
  zero 
  current, 
  with 
  appropriate 
  sign, 
  must 
  be 
  less 
  than 
  the 
  

   value 
  of 
  the 
  surface 
  discontinuity 
  which 
  would 
  be 
  due 
  to 
  the^ 
  

   projection, 
  alone, 
  of 
  that 
  class 
  of 
  ions 
  which 
  conditions 
  the 
  

   sign 
  of 
  the 
  potential-difference. 
  

  

  With 
  the 
  apparatus 
  described 
  in 
  a 
  previous 
  paper* 
  the- 
  

   potential-difference 
  for 
  zero 
  current 
  has 
  been 
  found 
  in 
  the 
  

   case 
  of 
  glowing 
  carbon 
  at 
  various 
  temperatures. 
  The 
  experi- 
  

   ments 
  were 
  a 
  continuation 
  of 
  the 
  work 
  already 
  described, 
  and 
  

   in 
  the 
  paper 
  just 
  mentioned 
  will 
  be 
  found 
  full 
  details 
  of 
  the 
  

   method 
  of 
  investigation. 
  The 
  observations, 
  which 
  fulfil 
  

   the 
  condition 
  that 
  the 
  values 
  should 
  be 
  independent 
  of 
  the 
  

   distance 
  separating 
  the 
  electrodes, 
  are 
  shown 
  in 
  the 
  figure. 
  

   For 
  zero 
  current 
  the 
  hot 
  carbon 
  was 
  positive 
  to 
  the 
  cooler 
  

   electrode 
  in 
  all 
  cases. 
  

  

  Potential-differences 
  for 
  zero 
  current. 
  

  

  18 
  

  

  

  X 
  

  

  Ot>s. 
  

  

  when 
  

  

  distance 
  

  

  befyi>een\ 
  carbons 
  

  

  = 
  2mm. 
  

  

  

  

  1 
  

   1 
  

  

  

  1 
  

  

  o 
  

  

  + 
  

  

  " 
  

  

  "■' 
  

  

  " 
  

  

  "" 
  

  

  ■ 
  

  

  = 
  3 
  // 
  

  

  = 
  4 
  -. 
  

  

  

  

  

  

  

  12 
  

  

  «l 
  

  

  

  

  

  

  1 
  

  

  

  

  

  / 
  

  

  

  ^ 
  

  

  

  

  

  

  

  

  

  

  

  

  / 
  

  

  

  

  1 
  

  

  

  

  

  

  

  

  

  

  

  / 
  

  

  

  

  

  

  

  

  

  

  

  

  

  / 
  

  

  

  

  1 
  

  

  

  

  

  

  

  

  

  

  / 
  

  

  

  

  

  i 
  

  

  

  

  

  

  

  

  

  ,^ 
  

  

  

  

  

  

  

  

  -^ 
  

   * 
  

  

  1^, 
  

  

  ■^ 
  

  

  ^ 
  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  UO 
  3 
  

  

  

  

  

  

  Temperature 
  

  

  Absolute. 
  

  

  The 
  heated 
  electrodes 
  were 
  cored 
  carbon 
  rods, 
  0*5 
  centi-^ 
  

   metre 
  in 
  diameter, 
  supplied 
  by 
  Messrs. 
  Siemens 
  Brothers 
  for 
  

   use 
  with 
  their 
  Lilliput 
  arc 
  lamps, 
  with 
  the 
  exception 
  of 
  the 
  

   one 
  employed 
  for 
  the 
  observation 
  at 
  3040° 
  absolute 
  which 
  

   was 
  a 
  squared 
  rod, 
  0*5 
  centimetre 
  on 
  the 
  side, 
  of 
  solid 
  

   Conradty 
  carbon 
  Marke 
  C. 
  As 
  the 
  measure 
  with 
  this 
  material 
  

   agrees 
  well 
  with 
  the 
  other 
  results, 
  it 
  may 
  be 
  concluded 
  that 
  

   * 
  PoUock 
  & 
  Ranclaiid, 
  Phil. 
  Mag. 
  March 
  1909, 
  p. 
  366. 
  

  

  