﻿702 
  Prof. 
  J. 
  de 
  Kowalski 
  and 
  Dr. 
  U. 
  J. 
  Rappel 
  on 
  

  

  difference 
  for 
  the 
  same 
  reading 
  of 
  the 
  milliamperemeter 
  was 
  

   0*2 
  per 
  cent. 
  The 
  phenomena 
  of 
  dilatation, 
  observed 
  by 
  

   Warburg* 
  and 
  others, 
  was 
  eliminated 
  by 
  the 
  use 
  of 
  an 
  

   arc-lamp. 
  

  

  The 
  alternating 
  current 
  milliamperemeter 
  was 
  carefully 
  

   calibrated. 
  It 
  was 
  capable 
  of 
  indicating 
  directly 
  to 
  30 
  milli- 
  

   amperes, 
  but 
  the 
  region 
  of 
  the 
  scale 
  between 
  10 
  and 
  27 
  was 
  

   exclusively 
  used, 
  because 
  the 
  readings 
  here 
  could 
  be 
  more 
  

   exactly 
  taken 
  to 
  the 
  hundredth 
  of 
  a 
  milliampere. 
  

  

  The 
  resistances 
  used 
  were 
  of 
  manganese 
  wire 
  and 
  free 
  from 
  

   self-induction. 
  Measurements 
  undertaken 
  previously 
  with 
  

   the 
  pendulum 
  of 
  Helmholtz 
  proved 
  that 
  the 
  self-induction 
  

   and 
  capacity 
  of 
  these 
  resistances 
  were 
  so 
  small 
  that 
  they 
  

   could 
  practically 
  be 
  neglected. 
  The 
  resistances 
  were 
  re- 
  

   peatedly 
  calibrated 
  by 
  comparison 
  with 
  normal 
  resistances, 
  

   the 
  latter 
  having 
  been 
  calibrated 
  by 
  the 
  Phys.-Technische 
  

   Reichsanstalt. 
  The 
  total 
  value 
  of 
  the 
  resistances 
  at 
  our 
  dis- 
  

   posal 
  was 
  1298800 
  ohms, 
  and 
  was 
  capable 
  of 
  carrying 
  a 
  

   current 
  of 
  30 
  milliamperes 
  for 
  a 
  length 
  of 
  time 
  without 
  

   being 
  appreciably 
  heated. 
  

  

  The 
  spheres 
  employed 
  as 
  electrodes 
  were 
  most 
  carefully 
  

   made 
  by 
  the 
  Societe 
  Genevoise. 
  There 
  were 
  6 
  pairs 
  of 
  

   spheres 
  with 
  the 
  following 
  diameters: 
  — 
  2, 
  3*85, 
  10, 
  15, 
  20, 
  

   and 
  30 
  cm. 
  Measurements 
  taken 
  with 
  the 
  cathetometer 
  

   showed 
  that 
  the 
  irregularities 
  in 
  the 
  construction 
  did 
  not 
  

   exceed 
  0*2 
  mm. 
  We 
  make 
  use 
  of 
  this 
  opportunity 
  to 
  thank 
  

   the 
  Societe 
  Genevoise 
  for 
  the 
  splendid 
  execution 
  of 
  this 
  

   difficult 
  task. 
  At 
  each 
  series 
  of 
  experiments 
  the 
  zero 
  for 
  

   the 
  distance 
  of 
  the 
  spheres 
  from 
  each 
  other 
  was 
  determined, 
  

   likewise 
  the 
  barometer 
  and 
  thermometer 
  readings. 
  

  

  Evidently 
  the 
  number 
  of 
  amperes 
  in 
  the 
  high-tension 
  

   circuit, 
  multiplied 
  by 
  the 
  number 
  of 
  ohms, 
  gives 
  the 
  value 
  of 
  

   the 
  effective 
  voltage, 
  whereas 
  to 
  determine 
  the 
  maximum 
  

   voltage 
  one 
  must 
  know 
  exactly 
  the 
  curve 
  of 
  tension. 
  For 
  

   this 
  purpose 
  an 
  oscillograph, 
  constructed 
  on 
  the 
  principle 
  of 
  

   Blondel, 
  by 
  the 
  firm 
  Siemens 
  and 
  Halske, 
  was 
  utilized. 
  The 
  

   high 
  periodicity 
  of 
  the 
  galvanometers 
  (frequency 
  to 
  6000 
  

   per 
  second) 
  permits 
  an 
  exact 
  reproduction 
  of 
  the 
  curve 
  with 
  

   an 
  alternating 
  current 
  whose 
  frequency 
  is 
  33. 
  In 
  sj)ite 
  of 
  

   the 
  grounding 
  of 
  one 
  of 
  the 
  poles, 
  the 
  greatest 
  care 
  nmst 
  be 
  

   exercised 
  because 
  of 
  the 
  extreme 
  danger 
  connected 
  with 
  the 
  

   work, 
  which 
  must 
  of 
  necessity 
  be 
  performed 
  in 
  the 
  dark. 
  

   From 
  the 
  oscillograms 
  and 
  the 
  milliampere 
  readings 
  the 
  

   maximum 
  voltage 
  is 
  deduced 
  according 
  to 
  the 
  method 
  in 
  

   common 
  use. 
  

  

  In 
  the 
  following 
  table 
  are 
  found 
  the 
  values 
  determined 
  

   for 
  the 
  ratio 
  of 
  the 
  effective 
  to 
  the 
  maximum 
  voltage 
  : 
  — 
  

   * 
  Warburg, 
  Ann. 
  d. 
  Phys. 
  v. 
  p. 
  811 
  (1901). 
  

  

  