﻿Trowbridge 
  — 
  Investigation 
  of 
  the 
  Coherer. 
  199 
  

  

  Aet. 
  XX. 
  — 
  A 
  Quantitative 
  Investigation 
  of 
  the 
  Coherer 
  ^ 
  

   bj 
  A. 
  Trowbeidge, 
  

  

  Since 
  the 
  very 
  remarkable 
  success 
  of 
  G. 
  Marconi 
  in 
  the 
  

   field 
  of 
  wireless 
  telegraphy, 
  a 
  renewed 
  interest 
  has 
  been 
  felt 
  

   by 
  physicists 
  in 
  the 
  coherer, 
  the 
  apparatus 
  devised 
  by 
  Branley 
  

   which 
  has 
  made 
  wireless 
  telegraphy 
  possible. 
  

  

  Besides 
  the 
  original 
  paper* 
  of 
  Branley 
  there 
  have 
  been 
  a 
  

   number 
  of 
  communications 
  on 
  the 
  subject 
  of 
  coherer 
  action 
  ; 
  

   in 
  particular 
  those 
  of 
  Dornf 
  and 
  Aschkinass,+ 
  which 
  have 
  

   thrown 
  much 
  light 
  on 
  the 
  subject. 
  As 
  yet, 
  however, 
  the 
  

   experimental 
  data 
  are 
  not 
  complete 
  enough 
  for 
  a 
  perfectly 
  

   satisfactory 
  theory 
  of 
  coherer 
  action 
  to 
  be 
  formed, 
  those 
  

   already 
  existing 
  being 
  seemingly 
  inadequate 
  to 
  explain 
  all 
  the 
  

   observed 
  phenomena. 
  

  

  Even 
  if 
  we 
  do 
  not 
  know 
  just 
  what 
  takes 
  place 
  in 
  the 
  coherer 
  

   itself, 
  we 
  know 
  that 
  the 
  cause 
  of 
  the 
  fall 
  in 
  resistance 
  is 
  pri- 
  

   marily 
  an 
  electro-magnetic 
  disturbance 
  in 
  the 
  space 
  surround- 
  

   ing 
  the 
  coherer. 
  This 
  disturbance 
  will 
  induce 
  a 
  static 
  wave 
  in 
  

   a 
  conductor 
  whose 
  direction 
  in 
  space 
  coincides 
  with 
  the 
  direc- 
  

   tion 
  of 
  the 
  lines 
  of 
  electric 
  force 
  from 
  the 
  source 
  of 
  the 
  electro- 
  

   magnetic 
  disturbance. 
  If 
  this 
  static 
  wave 
  is 
  the 
  cause 
  of 
  the 
  

   lowering 
  of 
  the 
  resistance 
  of 
  the 
  coherer, 
  then 
  a 
  static 
  dis- 
  

   charge 
  from 
  a 
  Leyden 
  jar, 
  or 
  electrophorus, 
  through 
  the 
  

   coherer, 
  should 
  produce 
  a 
  like 
  effect. 
  This 
  conclusion 
  was 
  

   verified 
  by 
  Professor 
  Henry 
  S. 
  Carhart 
  and 
  myself 
  while 
  we 
  

   were 
  engaged 
  a 
  few 
  months 
  ago 
  in 
  testing 
  the 
  sensibility 
  of 
  

   coherers 
  for 
  telegraphic 
  purposes. 
  If 
  this 
  conclusion 
  is 
  war- 
  

   ranted, 
  then 
  on 
  the 
  nature 
  of 
  the 
  discharge 
  and 
  the 
  quantity 
  

   of 
  electricity 
  which 
  goes 
  through 
  the 
  coherer 
  should 
  depend 
  

   the 
  fall 
  of 
  resistance 
  of 
  the 
  latter. 
  

  

  The 
  present 
  paper 
  has 
  to 
  deal 
  with 
  the 
  lowering 
  of 
  the 
  

   resistance 
  as 
  a 
  function 
  of 
  the 
  quantity 
  of 
  electricity 
  discharged 
  

   through 
  and 
  the 
  difference 
  of 
  potential 
  on 
  opposite 
  sides 
  of 
  the 
  

   coherer. 
  

  

  In 
  order 
  to 
  test 
  the 
  supposed 
  relation 
  between 
  quantity 
  of 
  

   electricity 
  discharged 
  and 
  the 
  fall 
  of 
  resistance 
  in 
  the 
  coherer, 
  

   I 
  adopted 
  the 
  following 
  arrangement. 
  

  

  By 
  means 
  of 
  a 
  charge 
  and 
  discharge 
  key, 
  a 
  subdivided 
  con- 
  

   denser 
  could 
  be 
  charged 
  from 
  a 
  large 
  storage 
  battery, 
  the 
  elec- 
  

   tromotive 
  force 
  of 
  which 
  could 
  be 
  varied 
  at 
  will 
  from 
  2 
  to 
  70 
  

   volts, 
  and 
  then 
  discharged 
  through 
  the 
  coherer. 
  The 
  capacity 
  

   at 
  my 
  disposal 
  could 
  be 
  varied 
  from 
  3*2 
  microfarad 
  to 
  0*05 
  

  

  * 
  Compt. 
  Eendus, 
  cxi. 
  f 
  Wied. 
  Ann., 
  Ixvi, 
  p. 
  146. 
  

  

  X 
  Wied. 
  Ann., 
  Ixvi, 
  p. 
  284. 
  

  

  