﻿Minimum 
  Spark 
  Potentials. 
  

  

  459 
  

  

  with 
  no 
  evidence 
  of 
  discharge, 
  the 
  potential 
  was 
  reduced 
  to 
  

   10 
  volts 
  and 
  the 
  distance 
  measured 
  through 
  which 
  the 
  

   electrodes 
  needed 
  to 
  move 
  to 
  give 
  short 
  circuit. 
  For 
  example, 
  

   using 
  two 
  platinum 
  spheres 
  each 
  approximately 
  *007 
  cm. 
  in 
  

   diameter 
  the 
  following 
  observations 
  are 
  noted 
  : 
  

  

  Applied 
  Potential. 
  

  

  Spark-gap. 
  

  

  Remarks. 
  

  

  325 
  volts. 
  

  

  1 
  wave-length. 
  

  

  No 
  spark. 
  

  

  275 
  „ 
  

  

  •8 
  

  

  ,, 
  

  

  310 
  „ 
  

  

  ■4 
  

  

  No 
  discharge. 
  

  

  310 
  „ 
  

  

  'DO 
  ., 
  

  

  No 
  discharge, 
  potential 
  applied 
  5 
  

   minutes. 
  

  

  340 
  „ 
  

  

  ■6 
  

  

  Discharge 
  occurred. 
  

  

  340 
  ., 
  

  

  1\3 
  wave-lengths. 
  

  

  j> 
  )• 
  

  

  340 
  „ 
  

  

  2-5 
  

  

  A 
  single 
  spark 
  occurred 
  but 
  no 
  

   second 
  could 
  be 
  obtained 
  at 
  

   that 
  potential. 
  

  

  365 
  „ 
  

  

  same. 
  

  

  Second 
  spark 
  occurred. 
  

  

  340 
  „ 
  

  

  3 
  wave-lengths. 
  

  

  A 
  single 
  spark. 
  

  

  340 
  „ 
  

  

  5 
  

  

  >> 
  •» 
  

  

  410 
  „ 
  

  

  10-5 
  

  

  Discharge 
  repeatedly. 
  

  

  Using 
  spheres 
  of 
  unequal 
  size, 
  with 
  diameters 
  '008 
  cm. 
  

   and 
  '0057 
  cm. 
  the 
  following 
  results 
  were 
  obtained 
  : 
  

  

  280 
  volts 
  

   310 
  „ 
  

   335 
  ., 
  

  

  350 
  „ 
  

  

  no 
  discharge 
  

  

  discharged 
  

  

  gap 
  measured 
  -8 
  wave-length. 
  

   ,, 
  '7 
  ,, 
  

  

  •6 
  

  

  Xext 
  a 
  pair 
  of 
  steel 
  needles 
  were 
  substituted 
  for 
  the 
  

   minute 
  spheres. 
  Xeedle-points 
  are 
  by 
  no 
  means 
  geometrically 
  

   pointed, 
  but 
  are 
  usually 
  more 
  approximately 
  parabolic, 
  in 
  the 
  

   axial 
  section. 
  The 
  appearance 
  of 
  the 
  needles 
  used, 
  as 
  seen 
  

   in 
  the 
  microscope, 
  is 
  shown 
  in 
  fig. 
  2; 
  the 
  diameter 
  at 
  a 
  

  

  Fiir. 
  2. 
  

  

  distance 
  from 
  the 
  tip 
  equal 
  to 
  the 
  radius 
  of 
  curvature 
  at 
  the 
  

   tip 
  was 
  approximately 
  '0007 
  cm. 
  With 
  two 
  such 
  electrodes 
  

   the 
  following 
  observations 
  dealing 
  with 
  spark-gaps 
  of 
  less 
  than 
  

   a 
  wave-length 
  of 
  sodium 
  light 
  were 
  made 
  : 
  

  

  320 
  volts 
  applied 
  ; 
  no 
  discharge 
  ; 
  gap 
  measured 
  "9 
  wave-length. 
  

  

  330 
  ,, 
  on 
  5 
  minutes, 
  no 
  discharge 
  ; 
  gap 
  "5 
  „ 
  

  

  330 
  ,, 
  applied 
  ; 
  no 
  discharge 
  ; 
  gap 
  measured 
  -25 
  ,, 
  

  

  