﻿from 
  an 
  Electrified 
  Point* 
  

  

  53 
  

  

  Table 
  V.- 
  

  

  -Air 
  37 
  cm. 
  pressure. 
  

   Point 
  - 
  

  

  Distances 
  

  

  Least 
  P.D. 
  

  

  Distances 
  

  

  Least 
  P.D. 
  

  

  in 
  

  

  required 
  

  

  in 
  

  

  required 
  

  

  wave-lengths 
  

  

  for 
  discharge. 
  

  

  wave-lengths 
  

  

  for 
  discharge. 
  

  

  Na 
  Jight. 
  

  

  Yolts. 
  

  

  Na 
  light. 
  

  

  Volts. 
  

  

  1 
  

  

  338 
  

  

  30 
  

  

  338 
  

  

  3 
  

  

  338 
  

  

  35 
  

  

  338 
  

  

  5 
  

  

  338 
  

  

  40 
  

  

  347 
  

  

  10 
  

  

  338 
  

  

  45 
  

  

  380 
  

  

  10 
  

  

  338 
  

  

  50 
  

  

  343 
  

  

  15 
  

  

  347 
  

  

  60 
  

  

  344 
  

  

  20 
  

  

  357 
  

  

  70 
  

  

  357 
  

  

  25 
  

  

  371 
  

  

  75 
  

  

  381 
  

  

  25 
  

  

  338 
  

  

  100 
  

  

  423 
  

  

  Table 
  VI. 
  

  

  -Air 
  25 
  cm. 
  pressure. 
  

   Point 
  - 
  

  

  Distances 
  in 
  wave-lengths 
  

   Na 
  light. 
  

  

  Least 
  P.D. 
  required 
  

   for 
  discharge. 
  

  

  Volts. 
  

  

  1 
  

   5 
  

  

  10 
  

   20 
  

   30 
  

   40 
  

   50 
  

   100 
  

   100 
  

  

  343 
  

  

  343 
  

  

  338 
  

   343 
  

   338 
  

   338 
  

   338 
  

   347 
  

   338 
  

  

  PI. 
  I. 
  fig. 
  1 
  represents 
  the 
  results 
  obtained 
  with 
  air 
  at 
  atmo- 
  

   spheric 
  pressure. 
  Reading 
  for 
  a 
  positive 
  point 
  is 
  indicated 
  

  

  by 
  a 
  circle 
  and 
  for 
  negative 
  by 
  a 
  cross 
  within 
  a 
  circle 
  (+). 
  

   The 
  dotted 
  curve 
  shows 
  the 
  potential-difference 
  required 
  for 
  

   a 
  spark 
  to 
  pass 
  between 
  a 
  plane 
  and 
  a 
  sphere, 
  the 
  sphere 
  

   having 
  dimensions 
  large 
  compared 
  with 
  the 
  distances 
  sepa- 
  

   rating 
  the 
  surfaces. 
  The 
  data 
  for 
  this 
  curve 
  are 
  taken 
  from 
  

   an 
  article 
  published 
  some 
  years 
  ago 
  by 
  the 
  author 
  (PhiL 
  

   Mag., 
  Jan. 
  1901, 
  p. 
  147). 
  

  

  PI. 
  I. 
  fig. 
  2 
  represents 
  values 
  obtained 
  for 
  point 
  positive 
  

   under 
  pressures 
  of 
  75 
  cm., 
  37 
  cm., 
  and 
  25 
  cm. 
  

  

  PI. 
  I. 
  fig. 
  3 
  in 
  a 
  similar 
  manner, 
  indicates 
  the 
  values 
  when 
  

   the 
  point 
  was 
  negative. 
  

  

  