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

  

  %r 
  

  

  water 
  pipes. 
  In 
  the 
  free 
  space 
  between 
  the 
  oscillator 
  and 
  

   reflector 
  moved 
  the 
  coherer 
  carriage. 
  The 
  dimensions 
  of 
  free 
  

   space 
  between 
  the 
  reflector 
  and 
  oscillator 
  were 
  12*67 
  m. 
  in 
  

   length, 
  6*15 
  m. 
  in 
  width 
  and 
  5*14 
  m'. 
  in 
  height. 
  The 
  nearest 
  

   wall 
  had 
  five 
  windows, 
  each 
  1-66 
  m. 
  by 
  1'12 
  m. 
  The 
  reflector 
  

   was 
  of 
  sheet 
  tin 
  3*32 
  m. 
  wide 
  by 
  4-24 
  m. 
  high. 
  

  

  The 
  oscillator, 
  the 
  coherer 
  globules 
  and 
  the 
  center 
  of 
  the 
  

   reflector 
  were 
  always 
  kept 
  in 
  the 
  same 
  horizontal 
  line. 
  The 
  

   oscillator 
  and 
  coherer 
  were 
  thus 
  2*25 
  m. 
  above 
  the 
  floor, 
  2*89 
  

   m. 
  below 
  the 
  ceiling 
  and 
  1*57 
  m. 
  from 
  the 
  nearest 
  wall, 
  which 
  

   ran 
  the 
  full 
  length 
  of 
  the 
  room. 
  By 
  moving 
  the 
  carriage 
  to 
  

   and 
  fro, 
  the 
  coherer 
  was 
  always 
  in 
  the 
  same 
  horizontal 
  line 
  at 
  

   any 
  desired 
  distance 
  from 
  the 
  reflector. 
  

  

  The 
  coherer 
  carriage 
  was 
  moved 
  to 
  any 
  distance 
  from 
  the 
  

   reflector, 
  its 
  globules 
  being 
  put 
  into 
  slightest 
  contact, 
  then 
  the 
  

   coherer 
  circuit 
  was 
  closed 
  by 
  touching 
  the 
  coherer 
  circuit 
  key 
  

   and 
  the 
  Mille-Ampere 
  meter 
  needle 
  reading 
  taken. 
  Upon 
  

   touching 
  the 
  key 
  in 
  the 
  oscillator 
  circuit, 
  sparking 
  at 
  the 
  oscil- 
  

   lator 
  began, 
  the 
  electric 
  waves 
  traversing 
  the 
  free 
  space 
  act 
  

   npon 
  the 
  coherer 
  and 
  at 
  once 
  there 
  is 
  or 
  is 
  not 
  an 
  increased 
  

   reading 
  given 
  by 
  the 
  Mille-Ampere 
  meter 
  needle. 
  By 
  moving 
  

   the 
  carriage 
  to 
  different 
  distances 
  from 
  the 
  reflector 
  and 
  repeat- 
  

   ing 
  the 
  above 
  operations 
  different 
  readings 
  are 
  found. 
  There 
  

   is 
  seen 
  to 
  be 
  a 
  regular 
  increase 
  and 
  decrease 
  in 
  the 
  Mille- 
  

   Ampere 
  meter 
  needle 
  readings 
  as 
  the 
  coherer 
  is 
  moved 
  farther 
  

   and 
  farther 
  from 
  the 
  reflector. 
  At 
  certain 
  places 
  no 
  change 
  in 
  

   the 
  readings 
  is 
  observed, 
  while 
  at 
  certain 
  other 
  places 
  there 
  is 
  

   a 
  maximum 
  reading. 
  Thus 
  by 
  means 
  of 
  the 
  coherer 
  we 
  are 
  

   enabled 
  to 
  locate 
  the 
  nodal 
  and 
  antinodal 
  points 
  of 
  the 
  electric 
  

   waves, 
  and 
  hence 
  we 
  determine 
  the 
  wave-length. 
  Many 
  pre- 
  

   cautions 
  had 
  to 
  be 
  taken 
  during 
  the 
  conduction 
  of 
  the 
  experi- 
  

   ment. 
  The 
  coherer 
  responds 
  to 
  any 
  (secondary) 
  electric 
  spark, 
  

   the 
  Mille-Ampere 
  meter 
  readings 
  differing 
  for 
  different 
  kinds 
  

   of 
  sparks. 
  Not 
  only 
  will 
  the 
  coherer 
  respond 
  to 
  the 
  sparks 
  

   from 
  the 
  oscillator, 
  but 
  it 
  responds 
  to 
  any 
  other 
  (secondary) 
  

   spark 
  which 
  at 
  the 
  time 
  may 
  have 
  taken 
  place 
  in 
  any 
  other 
  

   part 
  of 
  the 
  building 
  or 
  on 
  a 
  distant 
  trolley 
  wire. 
  So 
  sensitive 
  

   is 
  the 
  coherer, 
  the 
  slightest 
  jarring 
  of 
  the 
  room, 
  such 
  as 
  caused 
  

   by 
  the 
  slamming 
  of 
  a 
  door 
  or 
  of 
  the 
  walking 
  of 
  persons 
  in 
  the 
  

   corridor, 
  will 
  be 
  sufficient 
  to 
  very 
  materially 
  confuse 
  the 
  read- 
  

   ings. 
  Satisfactory 
  and 
  reliable 
  measurements 
  can 
  only 
  be 
  

   made, 
  when 
  such 
  disturbing 
  causes 
  are 
  not 
  present. 
  Accord- 
  

   ingly 
  the 
  night 
  hours 
  were 
  selected 
  in 
  which 
  to 
  carry 
  on 
  the 
  

   observations. 
  If 
  the 
  mercury 
  in 
  the 
  mercury 
  cup 
  of 
  the 
  break 
  

   becomes 
  coated, 
  the 
  nature 
  of 
  the 
  secondary 
  spark 
  changes 
  

   and 
  so 
  the 
  readings 
  under 
  such 
  conditions 
  are 
  not 
  proper. 
  If 
  a 
  

   too 
  strong 
  current 
  be 
  sent 
  up 
  from 
  the 
  storage 
  battery 
  into 
  the 
  

  

  