﻿Hlyh 
  Electromotive 
  Force, 
  99 
  

  

  variation 
  with 
  distance, 
  of 
  the 
  electrostatic 
  force 
  preceding 
  a 
  

   spark 
  at 
  the 
  greater 
  than 
  at 
  the 
  smaller 
  distance. 
  It 
  seems 
  

   most 
  probable 
  that 
  at 
  still 
  greater 
  distances 
  the 
  electrostatic 
  

   force 
  will 
  be 
  found 
  to 
  be 
  sensibly 
  constant, 
  as 
  it 
  was 
  certainly 
  

   expected 
  to 
  be 
  at 
  all 
  distances. 
  

  

  Having 
  at 
  my 
  command 
  a 
  very 
  much 
  improved 
  Plante 
  rheo- 
  

   static 
  machine 
  with 
  sixty 
  condensers 
  of 
  15 
  x 
  80 
  inches 
  coated 
  

   surface, 
  I 
  have 
  been 
  enabled 
  to 
  greatly 
  extend 
  my 
  studies 
  of 
  

   high 
  electromotive 
  force, 
  and 
  to 
  investigate 
  the 
  conditions 
  

   necessary 
  to 
  produce 
  sparks 
  of 
  great 
  body 
  forty-eight 
  to 
  fifty 
  

   inches 
  in 
  length. 
  The 
  accumulator 
  which 
  was 
  used 
  to 
  charge 
  

   the 
  rheostatic 
  machine 
  in 
  parallel 
  had 
  a 
  voltage 
  of 
  20,000, 
  

   and 
  the 
  machine 
  could 
  then 
  give 
  me 
  1,200,000 
  volts. 
  The 
  

   length 
  of 
  spark 
  which 
  corresponds 
  to 
  this 
  voltage 
  is 
  very 
  

   closely 
  forty-eight 
  inches. 
  Professor 
  EHhu 
  Thomson, 
  by 
  

   means 
  of 
  transformers, 
  has 
  obtained 
  sparks 
  of 
  fifty 
  to 
  sixty 
  

   inches 
  in 
  length, 
  and 
  has 
  estimated 
  the 
  necessary 
  voltage 
  to 
  

   produce 
  a 
  spark 
  of 
  80 
  centim. 
  at 
  500,000. 
  

  

  This 
  estimate 
  A. 
  Heydweiler* 
  thinks 
  is 
  very 
  much 
  too 
  great, 
  

   and 
  he 
  believes 
  that 
  100,000 
  would 
  be 
  nearer 
  the 
  truth. 
  My 
  

   investigations 
  show 
  conclusively 
  that 
  the 
  estimate 
  of 
  Professor 
  

   Thomson 
  is 
  far 
  nearer 
  the 
  truth 
  than 
  that 
  of 
  Heydweiler 
  ; 
  and 
  

   instead 
  of 
  being 
  lessened 
  it 
  should 
  be 
  increased. 
  

  

  In 
  a 
  recent 
  paper 
  on 
  the 
  tension 
  at 
  the 
  poles 
  of 
  induction- 
  

   apparatus, 
  A. 
  Oberbeck 
  f 
  states 
  that 
  a 
  potential-difference 
  of 
  

   60,000 
  volts 
  under 
  given 
  conditions 
  can 
  produce 
  a 
  spark 
  of 
  

   more 
  than 
  10 
  centim. 
  in 
  length. 
  It 
  is 
  difficult 
  to 
  obtain 
  con- 
  

   sistent 
  results 
  by 
  means 
  of 
  induction-coils 
  and 
  transformers. 
  

  

  My 
  results 
  show 
  that 
  Lord 
  Kelvin's 
  conjecture 
  that 
  the 
  

   electrostatic 
  force 
  necessary 
  to 
  produce 
  a 
  spark 
  in 
  air 
  remains 
  

   sensibly 
  constant 
  for 
  all 
  distances 
  beyond 
  the 
  limit 
  he 
  de- 
  

   scribes, 
  is 
  correct 
  ; 
  for 
  when 
  lengths 
  of 
  spark 
  are 
  plotted 
  as 
  

   abscissas, 
  and 
  the 
  corresponding 
  electromotive 
  forces 
  as 
  ordi- 
  

   nates, 
  a 
  straight 
  line 
  is 
  obtained. 
  Plante 
  calls 
  attention 
  to 
  the 
  

   fact 
  that 
  the 
  loss 
  of 
  energy 
  resulting 
  from 
  the 
  transformation 
  

   of 
  dynamic 
  into 
  static 
  electricity 
  is, 
  in 
  the 
  case 
  of 
  his 
  appa- 
  

   ratus, 
  much 
  less 
  than 
  in 
  induction 
  apparatus. 
  This 
  remark 
  

   applies 
  with 
  great 
  force 
  to 
  the 
  modern 
  use 
  of 
  transformers 
  for 
  

   the 
  production 
  of 
  high-tension 
  effects. 
  With 
  the 
  improved 
  

   form 
  of 
  rheostatic 
  machine 
  which 
  I 
  have 
  constructed, 
  one 
  

   third 
  of 
  a 
  horse-power 
  will 
  produce 
  the 
  effects 
  which 
  have 
  

   hitherto 
  required 
  the 
  employment 
  of 
  from 
  thirty 
  to 
  forty 
  horse- 
  

   power. 
  The 
  condensers 
  in 
  this 
  apparatus 
  are 
  very 
  uniform 
  

  

  * 
  Wied. 
  Ann. 
  xlviii. 
  p. 
  231 
  (1893). 
  

   t 
  Wied. 
  Ann. 
  No. 
  9, 
  p. 
  109 
  (1897). 
  

  

  H2 
  

  

  