﻿Dielectric 
  Constant 
  of 
  Paraffins. 
  57 
  

  

  electric 
  discharge 
  " 
  which 
  Hertz 
  * 
  has 
  so 
  thoroughly 
  in- 
  

   vestigated. 
  

  

  Positive 
  and 
  negative 
  surgings 
  start 
  at 
  the 
  middle 
  of 
  the 
  

   first 
  bridge 
  and 
  meet 
  in 
  opposite 
  phases 
  at 
  the 
  middle 
  of 
  

   the 
  second 
  bridge, 
  thus 
  forming, 
  according 
  to 
  Hertz, 
  potential 
  

   loops 
  at 
  points 
  midway 
  between 
  the 
  two 
  bridges 
  and 
  potential 
  

   nodes 
  at 
  the 
  middle 
  of 
  the 
  bridges. 
  The 
  distance 
  between 
  

   the 
  middle 
  points 
  of 
  the 
  bridges 
  is 
  a 
  half 
  wave-length, 
  the 
  

   value 
  of 
  which 
  can 
  be 
  found 
  by 
  adding 
  the 
  distance 
  between 
  

   the 
  two 
  wires 
  to 
  the 
  scale-reading. 
  It 
  is 
  doubtful 
  just 
  what 
  

   this 
  bridge 
  correction 
  ought 
  to 
  be, 
  but 
  the 
  determination 
  of 
  

   the 
  wave-length 
  by 
  another 
  method 
  (given 
  later) 
  seems 
  to 
  

   confirm 
  the 
  above 
  correction. 
  

  

  This 
  half- 
  wave 
  is 
  not 
  the 
  length 
  of 
  a 
  free 
  half- 
  wave 
  along 
  

   the 
  wires. 
  The 
  presence 
  of 
  the 
  tube 
  has 
  added 
  capacity 
  to 
  

   the 
  wires 
  and 
  thereby 
  shortened 
  the 
  wave. 
  The 
  tube 
  correction 
  

   must 
  therefore 
  be 
  determined. 
  To 
  do 
  this 
  find 
  the 
  position 
  

   of 
  the 
  second 
  node. 
  The 
  table 
  shows 
  this 
  to 
  be 
  58*94 
  cm. 
  

   Now 
  place 
  a 
  tube, 
  which 
  we 
  shall 
  call 
  the 
  balance-tube, 
  in 
  

   contact 
  with 
  the 
  wires 
  at 
  the 
  middle 
  of 
  the 
  second 
  potential 
  

   loop. 
  The 
  wave 
  is 
  now 
  shortened 
  by 
  an 
  amount 
  which 
  is 
  

   equal 
  to 
  the 
  tube 
  effect. 
  The 
  balance-tube 
  ought 
  to 
  be 
  of 
  the 
  

   same 
  diameter 
  as 
  the 
  argon 
  tube, 
  but 
  its 
  length 
  is 
  not 
  

   essential 
  provided 
  it 
  extends 
  beyond 
  the 
  two 
  wires. 
  The 
  

   balance-tube 
  as 
  well 
  as 
  the 
  argon 
  tube 
  ought 
  to 
  be 
  within 
  at 
  

   most 
  1 
  J 
  cm. 
  of 
  the 
  middle 
  of 
  the 
  loop, 
  otherwise 
  the 
  capacity 
  

   effect 
  is 
  lessened. 
  One-half 
  of 
  this 
  last 
  reading 
  (i. 
  e. 
  the 
  dis- 
  

   tance 
  between 
  the 
  first 
  bridge 
  and 
  the 
  second 
  node) 
  will 
  give 
  

   what 
  may 
  be 
  called 
  the 
  half 
  tube-ioave, 
  in 
  which 
  one 
  node 
  rests 
  

   on 
  the 
  wires 
  and 
  the 
  other 
  rests 
  on 
  the 
  centre 
  of 
  the 
  bridge. 
  

   We 
  shall 
  call 
  the 
  former 
  the 
  wire 
  node, 
  and 
  the 
  latter 
  the 
  

   bridge 
  node. 
  The 
  balance- 
  tube 
  may 
  now 
  be 
  removed 
  and 
  the 
  

   third 
  and 
  fourth 
  nodes 
  located, 
  leaving 
  the 
  argon 
  tube 
  at 
  the 
  

   first 
  potential 
  loop, 
  though 
  as 
  far 
  as 
  the 
  position 
  of 
  the 
  nodes 
  

   is 
  concerned 
  the 
  tube 
  may 
  be 
  placed 
  at 
  any 
  other 
  potential 
  

   loop. 
  If 
  we 
  add 
  the 
  tube 
  effect 
  to 
  the 
  average 
  reading 
  in 
  the 
  

   second 
  column, 
  and 
  also 
  the 
  distance 
  between 
  the 
  two 
  wires, 
  

   we 
  shall 
  get 
  what 
  may 
  be 
  called 
  a 
  wave-length 
  in 
  air. 
  (To 
  

   this 
  is 
  added 
  also 
  a 
  scale-correction 
  of 
  3 
  mm.) 
  This 
  is 
  in 
  

   fact 
  the 
  length 
  of 
  a 
  free 
  wave 
  along 
  the 
  wires, 
  but 
  since 
  the 
  

   experiments 
  of 
  Sarasin 
  and 
  De 
  La 
  Rive 
  have 
  f 
  shown 
  that 
  

   the 
  velocity 
  of 
  a 
  rapidly 
  oscillating 
  electrical 
  disturbance 
  

   along 
  a 
  wire 
  is 
  the 
  same 
  as 
  that 
  in 
  air, 
  we 
  have 
  good 
  authority 
  

   for 
  calling 
  the 
  above 
  the 
  wave-length 
  in 
  air. 
  

  

  * 
  < 
  Electric 
  Waves/ 
  p. 
  63. 
  

  

  t 
  Archives 
  des 
  Sciences 
  et 
  Naturelles 
  Geneve, 
  1890, 
  t. 
  xxiii. 
  p. 
  113. 
  

  

  