﻿NOV. 
  4, 
  1922 
  

  

  ZAHN 
  : 
  RECORDING 
  ELECTRIC 
  CONTACT 
  

  

  413 
  

  

  Spark, 
  by 
  means 
  of 
  the 
  high 
  voltage 
  induced 
  in 
  a 
  coil 
  whose 
  natural 
  

   frequency 
  is 
  the 
  same 
  as 
  that 
  of 
  the 
  applied 
  field. 
  (This 
  radio 
  fre- 
  

   quency 
  was 
  about 
  300,000 
  cycles 
  per 
  second.) 
  The 
  duration 
  of 
  this 
  

   spark 
  was 
  controlled 
  by 
  an 
  electric 
  contact 
  within 
  the 
  generator 
  cir- 
  

   cuit, 
  and 
  registered 
  by 
  letting 
  the 
  spark 
  puncture 
  a 
  moving 
  piece 
  of 
  

   carbon 
  paper. 
  It 
  was 
  a 
  matter 
  of 
  experiment 
  to 
  see 
  how 
  nearly 
  the 
  

   spark, 
  with 
  the 
  particular 
  arrangement 
  used, 
  followed 
  the 
  electric 
  

   contact 
  made 
  and 
  broken 
  in 
  the 
  generator 
  circuit. 
  

   The 
  exact 
  arrangement 
  of 
  apparatus 
  which 
  was 
  first 
  used 
  is 
  shown 
  in 
  

   Fig. 
  1. 
  It 
  consists 
  of 
  a 
  simple 
  electron 
  tube 
  generator 
  and 
  a 
  rotating 
  

   chopper 
  K 
  used 
  to 
  make 
  and 
  to 
  break 
  the 
  contact 
  at 
  the 
  filament 
  

   terminal 
  of 
  the 
  tube 
  and 
  thus 
  to 
  start 
  and 
  to 
  stop 
  the 
  generation 
  of 
  

   radio-frequency 
  current, 
  respectively. 
  The 
  coil 
  Ls 
  is 
  a 
  large 
  coil 
  of 
  

  

  Fig. 
  1. 
  Generating 
  circuit, 
  commutation 
  at 
  filament 
  terminal. 
  

  

  the 
  type 
  known 
  as 
  "stagger 
  wound" 
  or 
  sometimes 
  as 
  "spider 
  web," 
  

   and 
  has 
  a 
  natural 
  frequency 
  of 
  such 
  a 
  value 
  that 
  the 
  generator 
  can 
  be 
  

   tuned 
  to 
  it 
  by 
  means 
  of 
  the 
  condenser 
  C. 
  By 
  means 
  of 
  coupling 
  the 
  

   coil 
  Ls 
  with 
  coils 
  Li 
  and 
  L2, 
  which 
  are 
  coupled 
  to. 
  each 
  other, 
  and 
  

   tuning, 
  a 
  radio 
  -frequency 
  voltage 
  is 
  induced 
  in 
  the 
  coil 
  L3 
  sufficient 
  to 
  

   maintain 
  a 
  series 
  of 
  sparks 
  between 
  the 
  coil 
  terminals 
  when 
  they 
  are 
  

   brought 
  close 
  together 
  as 
  shown 
  in 
  Fig. 
  1 
  . 
  The 
  duration 
  of 
  this 
  series 
  

   of 
  sparks 
  is 
  registered 
  in 
  the 
  following 
  manner. 
  The 
  chopper 
  K 
  is 
  

   divided 
  into 
  alternate 
  equal 
  segments 
  of 
  insulating 
  and 
  conducting 
  

   material 
  so 
  that 
  the 
  spark 
  exists 
  for 
  equal 
  time 
  intervals 
  separated 
  by 
  

   time 
  inter\^als 
  equal 
  to 
  those 
  of 
  the 
  spark 
  duration 
  . 
  A 
  piece 
  of 
  carbon 
  

   paper 
  in 
  the 
  form 
  of 
  a 
  cylinder 
  is 
  made 
  to 
  rotate 
  about 
  its 
  axis 
  in 
  

   synchronism 
  with 
  the 
  chopper 
  by 
  having 
  it 
  wrapped 
  around 
  a 
  brass 
  

   drum 
  which 
  is 
  mechanically 
  coupled 
  to 
  the 
  shaft 
  which 
  rotates 
  the 
  

  

  