﻿414 
  JOURNAI, 
  OF 
  THE 
  WASHINGTON 
  ACADEMY 
  OF 
  SCIENCES 
  VOL. 
  12, 
  NO. 
  18 
  

  

  chopper. 
  One 
  terminal 
  of 
  the 
  coil 
  L3 
  is 
  connected 
  to 
  this 
  brass 
  

   drum 
  and 
  the 
  other 
  terminal 
  in 
  the 
  form 
  of 
  a 
  needle 
  point 
  is 
  fastened 
  

   within 
  a 
  millimeter's 
  distance 
  from 
  the 
  carbon 
  paper. 
  During 
  the 
  

   time 
  when 
  the 
  chopper 
  makes 
  contact 
  a 
  spark 
  passes 
  between 
  the 
  

   needle 
  point 
  and 
  the 
  brass 
  drum 
  through 
  the 
  carbon 
  paper, 
  and 
  while 
  

   the 
  contact 
  is 
  interrupted 
  no 
  spark 
  passes. 
  Thus 
  the 
  carbon 
  paper 
  

   is 
  punctured 
  at 
  equal 
  intervals 
  around 
  the 
  cylinder. 
  

  

  The 
  arrangement 
  of 
  apparatus 
  for 
  another 
  method 
  of 
  controlling 
  

   the 
  radio-frequency 
  current 
  is 
  shown 
  in 
  Fig. 
  2. 
  Here 
  a 
  resistance 
  R 
  

   of 
  about 
  10 
  ohms, 
  sufficient 
  to 
  prevent 
  the 
  generation 
  of 
  radio-fre- 
  

   quency 
  current, 
  is 
  inserted 
  in 
  the 
  oscillating 
  circuit 
  of 
  the 
  tube. 
  The 
  

   chopper 
  is 
  connected 
  across 
  this 
  resistance. 
  When 
  this 
  resistance 
  is 
  

   short 
  circuited 
  by 
  the 
  chopper, 
  radio-frequency 
  current 
  is 
  generated. 
  

  

  Fig. 
  2. 
  Generating 
  circuit, 
  commutation 
  by 
  inserting 
  resistance. 
  

  

  This 
  latter 
  method 
  is 
  better 
  for 
  cases 
  where 
  sparking 
  at 
  the 
  contact 
  is 
  

   objectionable, 
  for 
  in 
  the 
  former 
  method 
  the 
  chopper 
  interrupts 
  the 
  

   plate 
  current. 
  

  

  The 
  following 
  experimental 
  details 
  may 
  be 
  of 
  interest. 
  Several 
  

   types 
  of 
  coil 
  for 
  .L3 
  and 
  several 
  types 
  of 
  electron 
  tubes 
  were 
  tried. 
  

   The 
  stagger-wound 
  coil 
  gave 
  the 
  best 
  results 
  as 
  regards 
  power 
  con- 
  

   siderations. 
  At 
  first 
  a 
  General 
  Electric 
  Type 
  P 
  pliotron 
  tube 
  rated 
  

   at 
  250 
  watts 
  was 
  used 
  at 
  rated 
  plate 
  voltages. 
  This 
  gave 
  much 
  more 
  

   power 
  than 
  was 
  necessary, 
  so 
  several 
  other 
  combinations 
  were 
  tried, 
  

   to 
  see 
  whether 
  enough 
  power 
  could 
  be 
  generated 
  using 
  220 
  volts 
  on 
  

   the 
  plate 
  of 
  the 
  tube. 
  With 
  this 
  latter 
  plate 
  voltage 
  neither 
  a 
  General 
  

   Electric 
  Type 
  P 
  250-watt 
  tube, 
  nor 
  two 
  General 
  Electric 
  Type 
  U 
  50- 
  

   watt 
  tubes, 
  nor 
  four 
  Western 
  Electric 
  Type 
  E 
  5-watt 
  tubes 
  gave 
  suffi- 
  

   cient 
  power 
  : 
  therefore, 
  it 
  was 
  decided 
  to 
  use 
  a 
  single 
  Type 
  U 
  tube 
  with 
  

   500 
  volts 
  on 
  the 
  plate. 
  

  

  