﻿G. 
  V. 
  Maclean 
  — 
  Velocity 
  of 
  Electric 
  Waves 
  m 
  A 
  

  

  t7\ 
  

  

  Marconi 
  coherer 
  and 
  a 
  galvanometer. 
  The 
  readings 
  of 
  his 
  

   galvanometer, 
  as 
  he 
  moved 
  the 
  coherer 
  farther 
  and 
  farther 
  

   from 
  the 
  reflector, 
  changed 
  ; 
  no 
  zero 
  readings, 
  however, 
  were 
  

   found 
  and 
  there 
  was 
  no 
  regular 
  increase 
  or 
  decrease 
  in 
  the 
  

   readings. 
  The 
  following 
  table 
  is 
  taken 
  from 
  his 
  paper 
  : 
  

  

  Distance 
  of 
  Coherer 
  

  

  

  Distance 
  of 
  Coherer 
  

  

  

  in 
  cms. 
  

  

  from 
  

  

  Deflection 
  of 
  

  

  in 
  cms. 
  from 
  

  

  Deflection 
  of 
  

  

  Reflector. 
  

  

  Galv. 
  Needle. 
  

  

  Reflector. 
  

  

  Galv. 
  Needle 
  

  

  2 
  

  

  

  12 
  

  

  60 
  

  

  15-4 
  

  

  5 
  

  

  

  13-4 
  

  

  65 
  

  

  16-0 
  

  

  10 
  

  

  

  16-2 
  

  

  70 
  

  

  17-0 
  

  

  15 
  

  

  

  16-3 
  

  

  Y5 
  

  

  16-5 
  

  

  20 
  

  

  

  ]6'4 
  

  

  80 
  

  

  16-2 
  

  

  25 
  

  

  

  15*5 
  

  

  90 
  

  

  15-8 
  

  

  30 
  

  

  

  15-8 
  

  

  100 
  

  

  16-2 
  

  

  35 
  

  

  

  15*5 
  

  

  110 
  

  

  16-5 
  

  

  40 
  

  

  

  15-8 
  

  

  120 
  

  

  16-0 
  

  

  45 
  

  

  

  15-5 
  

  

  130 
  

  

  16-3 
  

  

  50 
  

  

  

  15*5 
  

  

  140 
  

  

  16-4 
  

  

  55 
  

  

  

  10-0 
  

  

  150 
  

   200 
  

  

  17-2 
  

   17-4 
  

  

  His 
  results 
  were 
  submitted 
  to 
  Professor 
  A. 
  Righi, 
  who 
  with 
  

   Professor 
  Murani, 
  concluded 
  that 
  the 
  coherer 
  was 
  unsuitable 
  

   for 
  the 
  measurement 
  of 
  stationary 
  electric 
  waves. 
  

  

  Le 
  Royer 
  and 
  Paul 
  von 
  Berchem"^ 
  at 
  Geneva, 
  in 
  April 
  of 
  

   1894, 
  used 
  a 
  coherer 
  containing 
  iron 
  filings 
  kept 
  between 
  two 
  

   magnetized 
  needles. 
  Their 
  results 
  showed 
  that 
  the 
  tube 
  they 
  

   employed 
  had 
  not 
  a 
  wave-length 
  peculiar 
  to 
  itself 
  and 
  that 
  it 
  

   acted 
  as 
  an 
  analyser 
  and 
  not 
  as 
  a 
  resonator, 
  and 
  that 
  it 
  would 
  

   serve 
  to 
  measure 
  the 
  electric 
  wave-lengths 
  in 
  air. 
  

  

  The 
  coherer 
  here 
  employed 
  is 
  one 
  reduced 
  to 
  its 
  elements. 
  

   It 
  might 
  in 
  fact 
  be 
  termed 
  an 
  electro-bolometer, 
  and 
  in 
  

   general 
  is 
  not 
  more 
  difficult 
  to 
  use 
  than 
  the 
  heat-bolometer. 
  

  

  Two 
  globules 
  of 
  platinum, 
  one 
  mm. 
  in 
  diameter, 
  are 
  attached 
  

   to 
  the 
  ends 
  of 
  two 
  platinum 
  wares 
  0'12 
  mm. 
  in 
  diameter 
  and 
  

   1*7 
  cm. 
  in 
  length. 
  These 
  latter 
  form 
  spirals 
  each 
  of 
  two 
  con- 
  

   volutions 
  about 
  two 
  iron 
  terminals 
  1'5 
  mm. 
  in 
  diameter 
  and 
  

   4 
  cm. 
  in 
  length. 
  These 
  terminals 
  run 
  through 
  the 
  center 
  of 
  

   the 
  two 
  brass 
  caps 
  of 
  a 
  glass 
  tube 
  8*5 
  cms. 
  long 
  and 
  1"5 
  cms. 
  in 
  

   diameter. 
  To 
  one 
  of 
  the 
  terminals 
  was 
  connected 
  a 
  mill-head 
  

   screw, 
  so 
  that 
  the 
  platinum 
  globules 
  could 
  be 
  adjusted 
  to 
  any 
  

   distance 
  from 
  each 
  other. 
  This 
  constitutes 
  the 
  coherer 
  proper. 
  

   The 
  glass 
  tube 
  is 
  not 
  exhausted 
  ; 
  it 
  serves 
  merely 
  to 
  protect 
  

   the 
  globules 
  from 
  dust, 
  dampness, 
  or 
  other 
  external 
  interfer- 
  

   •ences. 
  The 
  coherer 
  is 
  placed 
  in 
  circuit 
  with 
  a 
  large 
  Yolta- 
  

  

  * 
  Bibliotheque 
  Univ. 
  Archives 
  de 
  Geneve, 
  xxsi, 
  1894, 
  p. 
  558. 
  

  

  