﻿204 
  Trowbridge 
  — 
  Investigation 
  of 
  the 
  Coherer. 
  

  

  that 
  r"^ 
  > 
  4 
  -^5 
  or 
  that 
  the 
  discharge 
  which 
  affects 
  the 
  lowering 
  

  

  of 
  resistance 
  in 
  this 
  investigation 
  was 
  aperiodic. 
  I 
  tested 
  

   this 
  point 
  experimentally 
  in 
  the 
  following 
  manner 
  : 
  the 
  con- 
  

   denser 
  was 
  removed 
  and 
  the 
  lead- 
  wires 
  from 
  tlie 
  storage 
  bat- 
  

   tery 
  to 
  the 
  ends 
  of 
  the 
  coherer 
  were 
  provided 
  with 
  a 
  key 
  and 
  

   a 
  thin 
  yL- 
  ampere 
  fuse-wire 
  in 
  series. 
  When 
  the 
  key 
  was 
  

   closed 
  a 
  steady 
  current 
  flowed 
  through 
  the 
  coherer 
  — 
  the 
  volt- 
  

   age 
  of 
  the 
  storage 
  battery 
  was 
  varied 
  through 
  a 
  range 
  of 
  from 
  

   8-70 
  volts, 
  and 
  the 
  lowering 
  of 
  the 
  resistance 
  of 
  the 
  coherer 
  

   was 
  again 
  found 
  to 
  vary 
  as 
  the 
  voltage. 
  Owing 
  to 
  the 
  element 
  

   of 
  time 
  entering 
  into 
  the 
  problem 
  (the 
  time 
  elapsing 
  from 
  the 
  

   closing 
  of 
  the 
  key 
  to 
  the 
  blowing 
  out 
  of 
  the 
  fuse), 
  it 
  was 
  not 
  

   possible 
  to 
  make 
  quantitative 
  observations 
  on 
  the 
  fall 
  of 
  resist- 
  

   ance. 
  It 
  was 
  evident, 
  however, 
  that 
  a 
  steady 
  current 
  did 
  

   produce 
  this 
  drop 
  in 
  resistance, 
  that 
  the 
  drop 
  was 
  greater 
  the 
  

   greater 
  the 
  electromotive 
  force 
  of 
  the 
  storage 
  battery, 
  and 
  

   further, 
  as 
  I 
  had 
  before 
  noted, 
  that 
  for 
  an 
  electromotive 
  

   force 
  less 
  than 
  from 
  8-10 
  volts 
  no 
  coherer 
  action 
  took 
  place. 
  

  

  ]^ow 
  we 
  can 
  regard 
  the 
  coherer 
  with 
  its 
  vertical 
  wire 
  and 
  

   earth 
  connection, 
  as 
  it 
  is 
  used 
  by 
  Marconi, 
  as 
  part 
  of 
  the 
  dis- 
  

   charged 
  circuit 
  of 
  a 
  condenser 
  whose 
  plates 
  are 
  the 
  vertical 
  

   wire 
  and 
  the 
  earth. 
  A 
  certain 
  potential 
  difference 
  between 
  

   vertical 
  wire 
  and 
  earth 
  is 
  caused 
  by 
  the 
  electromagnetic 
  waves 
  

   sent 
  out 
  from 
  the 
  Herz 
  oscillator 
  ; 
  this 
  potential 
  and 
  the 
  

   capacity 
  of 
  the 
  vertical 
  wire 
  — 
  earth 
  condenser 
  determine 
  the 
  

   quantity 
  of 
  electricity 
  which 
  is 
  discharged 
  through 
  the 
  

   coherer 
  in 
  the 
  form 
  of 
  an 
  aperiodic 
  impulse 
  and 
  which 
  pro- 
  

   duces 
  the 
  lowering 
  in 
  resistance 
  necessary 
  to 
  wireless 
  tele- 
  

   graphy. 
  The 
  potential 
  difference 
  on 
  opposite 
  sides 
  of 
  the 
  

   coherer 
  must 
  be 
  an 
  inverse 
  function 
  of 
  the 
  distance 
  between 
  

   sending 
  and 
  receiving 
  stations 
  ; 
  if 
  this 
  distance 
  is 
  small, 
  the 
  

   potential 
  difference 
  being 
  above 
  what 
  I 
  have 
  called 
  the 
  critical 
  

   potential 
  for 
  the 
  coherer 
  used, 
  if 
  we 
  increase 
  the 
  capacity 
  of 
  

   the 
  vertical 
  wire 
  we 
  shall 
  increase 
  the 
  fall 
  in 
  resistance 
  of 
  the 
  

   coherer, 
  but 
  if 
  the 
  distance 
  is 
  so 
  great 
  that 
  the 
  potential 
  is 
  at 
  

   about 
  its 
  critical 
  value, 
  then 
  an 
  increase 
  in 
  capacity 
  would 
  

   lower 
  the 
  potential 
  and 
  so 
  diminish 
  or 
  destroy 
  the 
  sensibility 
  

   of 
  the 
  coherer. 
  

  

  This 
  would 
  explain 
  Marconi's 
  statement 
  that 
  at 
  short 
  dis- 
  

   tances 
  a 
  capacity 
  consisting 
  of 
  a 
  cubical 
  tin 
  box 
  mounted 
  at 
  

   the 
  top 
  of 
  the 
  vertical 
  wire, 
  increased 
  the 
  sensibility 
  of 
  the 
  

   coherer, 
  but 
  that 
  he 
  found 
  it 
  advisable 
  to 
  omit 
  this 
  capacity 
  

   when 
  telegraphing 
  long 
  distances. 
  

  

  It 
  is 
  also 
  evident 
  that 
  one 
  precaution 
  must 
  be 
  taken 
  when 
  

   using 
  a 
  very 
  sensitive 
  coherer 
  for 
  wireless 
  telegraphy. 
  Since 
  

  

  