﻿266 
  Dr. 
  A. 
  M. 
  Tyndall 
  and 
  Miss 
  Searle 
  on 
  the 
  

  

  the 
  electrometer, 
  and 
  one 
  pole 
  of 
  the 
  dynamo 
  were 
  earthed. 
  

   The 
  wire 
  also 
  formed 
  part 
  o£ 
  a 
  separate 
  heating 
  circuit 
  ; 
  the 
  

   heat 
  generated 
  in 
  the 
  wire 
  was 
  measured 
  by 
  a 
  voltmeter 
  

   and 
  a 
  milliammeter, 
  The 
  electrical 
  arrangements 
  included 
  

   a 
  key 
  so 
  arranged 
  that 
  the 
  discharge 
  and 
  heating 
  currents 
  

   could 
  be 
  switched 
  on 
  simultaneously 
  or 
  separately, 
  as 
  

   desired. 
  

  

  It 
  may 
  be 
  noted 
  in 
  passing 
  that 
  the 
  tube 
  for 
  which 
  

   Farwell 
  gives 
  dimensions 
  was 
  4*45 
  cm., 
  and 
  the 
  wire 
  

   *019 
  mm. 
  in 
  diameter. 
  This 
  necessitated 
  the 
  use 
  of 
  higher 
  

   potentials, 
  but 
  these 
  were 
  not 
  so 
  convenient 
  in 
  the 
  present 
  

   experiments. 
  

  

  In 
  Table 
  I. 
  some 
  results 
  for 
  positive 
  and 
  negative 
  discharge 
  

   are 
  given 
  ; 
  u 
  p 
  t 
  — 
  p 
  Q 
  >y 
  is 
  the 
  initial 
  corona 
  pressure 
  effect 
  due 
  

   to 
  a 
  current 
  " 
  i 
  " 
  and 
  a 
  potential 
  difference 
  " 
  e" 
  The 
  last 
  

   column 
  gives 
  the 
  ratio 
  of 
  " 
  p± 
  — 
  p 
  " 
  to 
  "ie," 
  the 
  watts 
  dissi- 
  

   pated 
  in 
  the 
  tube. 
  

  

  Table 
  I. 
  

  

  Sign 
  of 
  

  

  

  i 
  

  

  e 
  

  

  Pi-Po 
  

  

  Discharge. 
  

  

  P\-Po- 
  

  

  2 
  X 
  10" 
  3 
  amp. 
  

  

  volts. 
  

  

  ie 
  

  

  + 
  

  

  •08 
  (?) 
  

  

  62 
  

  

  4450 
  

  

  296 
  (?) 
  

  

  

  •13 
  

  

  165 
  

  

  4620 
  

  

  1-78 
  

  

  

  •16 
  

  

  22-6 
  

  

  4600 
  

  

  1-58 
  

  

  

  •20 
  

  

  274 
  

  

  4780 
  

  

  1-50 
  

  

  

  •24 
  

  

  341 
  

  

  4780 
  

  

  1-51 
  

  

  

  •35 
  

  

  55-5 
  

  

  5050 
  

  

  1-26 
  

  

  

  •46 
  

  

  76-0 
  

  

  5200 
  

  

  117 
  

  

  

  •52 
  

  

  87-0 
  

  

  5230 
  

  

  113 
  

  

  

  •66 
  

  

  1100 
  

  

  5350 
  

  

  111 
  

  

  

  •71 
  

  

  120-0 
  

  

  5500 
  

  

  1-08 
  

  

  _ 
  

  

  •09 
  

  

  21-7 
  

  

  4700 
  

  

  •90 
  

  

  

  •16 
  

  

  354 
  

  

  4820 
  

  

  •91 
  

  

  

  •20 
  

  

  44-5 
  

  

  4770 
  

  

  •93 
  

  

  

  •29 
  

  

  64-2 
  

  

  5030 
  

  

  •91 
  

  

  

  •37 
  

  

  81-0 
  

  

  5150 
  

  

  •89 
  

  

  

  •42 
  

  

  943 
  

  

  5200 
  

  

  •86 
  

  

  

  •77 
  

  

  1690 
  

  

  5400 
  

  

  •84 
  

  

  

  1-01 
  

  

  220-0 
  

  

  5480 
  

  

  •84 
  

  

  It 
  will 
  be 
  noticed 
  that 
  in 
  positive 
  discharge 
  the 
  ratio 
  shows 
  

   a 
  marked 
  decrease 
  in 
  value 
  as 
  the 
  current 
  increases, 
  though 
  

   it 
  appears 
  to 
  approach 
  some 
  limiting 
  value 
  at 
  still 
  higher 
  

   currents. 
  This 
  decrease 
  may 
  be 
  attributed 
  to 
  the 
  growing 
  

   strength 
  o£ 
  the 
  wind 
  as 
  the 
  current 
  increases. 
  Though 
  a 
  

   decrease 
  is 
  also 
  observable 
  in 
  negative 
  discharge, 
  it 
  is 
  much 
  

   smaller. 
  

  

  