﻿Propagation 
  of 
  Alternate 
  Currents 
  in 
  Cables. 
  719 
  

  

  This 
  helix 
  is 
  supported 
  in 
  a 
  wooden 
  frame, 
  and 
  has 
  above 
  

   it 
  a 
  carbon-dioxide 
  vacuum-tube 
  1 
  inch 
  diameter. 
  Immediately 
  

   below 
  the 
  helix 
  and 
  about 
  2 
  mm. 
  from 
  it 
  are 
  the 
  spherical 
  

   bulbs 
  of 
  18 
  vertical 
  carbon-dioxide 
  tubes, 
  which 
  are 
  mounted 
  

   in 
  brass 
  sockets 
  on 
  a 
  metal 
  strip 
  fixed 
  to 
  a 
  shelf 
  at 
  the 
  

   bottom. 
  

  

  The 
  helix 
  is 
  excited 
  from 
  a 
  10 
  in.-spark 
  induction-coil 
  with 
  

   an 
  oscillation-circuit 
  consisting 
  of 
  six 
  leyden-jars 
  of 
  about 
  

   •002 
  microfarad 
  each, 
  which 
  can 
  be 
  connected 
  in 
  series 
  or 
  

   parallel 
  ; 
  and 
  an 
  adjustable 
  helix 
  having 
  a 
  maximum 
  in- 
  

   ductance 
  of 
  '000365 
  henry. 
  

  

  In 
  order 
  to 
  exhibit 
  the 
  effect 
  of 
  different 
  receivers 
  at 
  the 
  

   end 
  of 
  the 
  line 
  a 
  water 
  resistance, 
  consisting 
  of 
  a 
  tube 
  about 
  

   5 
  mrns. 
  diameter 
  and 
  30 
  cms. 
  long, 
  was 
  made 
  up, 
  as 
  well 
  as 
  

   an 
  adjustable 
  parallel-plate 
  condenser 
  about 
  *7 
  sq. 
  ft. 
  in 
  area, 
  

   and 
  an 
  inductance-coil 
  of 
  110 
  yards 
  of 
  No. 
  16 
  Gr.P. 
  covered 
  

   wire 
  in 
  a 
  hank 
  about 
  10 
  in. 
  diameter. 
  By 
  means 
  of 
  mercury 
  

   cups 
  and 
  paraffin 
  blocks, 
  various 
  arrangements 
  of 
  leyden-jars 
  

   and 
  loads 
  could 
  be 
  easily 
  made. 
  

  

  The 
  photographs, 
  figs. 
  2 
  to 
  9 
  (PI. 
  XXIII.), 
  are 
  of 
  the 
  appa- 
  

   ratus, 
  and 
  of 
  the 
  effects 
  observed 
  when 
  currents 
  of 
  different 
  

   frequency 
  were 
  employed, 
  and 
  different 
  terminal 
  conditions. 
  

   The 
  sending 
  end 
  was 
  in 
  each 
  case 
  on 
  the 
  left. 
  In 
  figs. 
  3, 
  

   4, 
  and 
  5 
  the 
  frequencies 
  were 
  about 
  600,000, 
  1,140,000, 
  and 
  

   1,800,000~ 
  per 
  sec. 
  respectively, 
  giving 
  one, 
  two, 
  and 
  three 
  

   half 
  -waves. 
  In 
  each 
  case 
  the 
  current 
  and 
  potential 
  waves 
  

   are 
  out 
  of 
  phase 
  ; 
  and 
  at 
  the 
  higher 
  frequency, 
  where 
  resist- 
  

   ance 
  is 
  of 
  less 
  effect, 
  they 
  are 
  almost 
  exactly 
  in 
  quadrature, 
  

   as 
  required 
  by 
  theory. 
  

  

  The 
  remaining 
  figures 
  are 
  all 
  with 
  the 
  low 
  frequency 
  and 
  

   should 
  be 
  compared 
  with 
  fig. 
  3. 
  Fig. 
  6 
  shows 
  the 
  effect 
  of 
  

   earthing 
  the 
  receiving 
  end 
  through 
  the 
  water 
  resistance; 
  and 
  

   that, 
  as 
  theory 
  indicates, 
  the 
  current 
  and 
  P.D. 
  become 
  much 
  

   more 
  uniform 
  in 
  magnitude. 
  In 
  fig. 
  7 
  the 
  receiving 
  end 
  is 
  

   earthed, 
  resulting 
  in 
  a 
  shifting 
  of 
  the 
  waves 
  to 
  the 
  right, 
  so 
  

   that 
  a 
  second 
  current-loop 
  appears. 
  

  

  Fig. 
  8 
  illustrates 
  the 
  effect 
  of 
  increasing 
  the 
  capacity 
  of 
  the 
  

   helix 
  by 
  introducing 
  an 
  earthed 
  wire 
  inside 
  it, 
  and 
  shows 
  that 
  

   with 
  the 
  same 
  frequency 
  the 
  wave-length 
  is 
  decreased, 
  so 
  

   that 
  there 
  are 
  two 
  half-waves 
  instead 
  of 
  one. 
  

  

  Finally, 
  fig. 
  9 
  shows 
  the 
  effect 
  of 
  earthing 
  the 
  receiving 
  end 
  

   through 
  a 
  condenser. 
  The 
  current-loops 
  are 
  shifted 
  forward 
  

   as 
  when 
  the 
  receiving 
  end 
  was 
  earthed, 
  and 
  at 
  the 
  same 
  time 
  

   they 
  are 
  much 
  more 
  definite. 
  With 
  inductance 
  the 
  same 
  

   result 
  is 
  observed, 
  but 
  the 
  shift 
  is 
  backward, 
  as 
  the 
  theory 
  

   indicates. 
  

  

  