﻿1875.] 
  Electrical 
  Discharges 
  through 
  Rarefied 
  Gases. 
  457 
  

  

  coupled 
  with 
  the 
  extreme 
  rapidity 
  and 
  consequent 
  decision 
  of 
  make 
  and 
  

   break, 
  that 
  I 
  mainly 
  attribute 
  the 
  steadiness 
  of 
  the 
  results. 
  

  

  The 
  rod 
  bore 
  a 
  plate 
  of 
  platinum, 
  hammered 
  hard, 
  on 
  its 
  upperside 
  ; 
  

   and 
  when 
  contact 
  was 
  made 
  this 
  plate 
  met 
  a 
  thin 
  platinum 
  pin 
  connected 
  

   with 
  the 
  circuit. 
  In 
  order 
  to 
  avoid, 
  as 
  far 
  as 
  possible, 
  any 
  uncertainty 
  in 
  

   contact, 
  the 
  diameter 
  of 
  this 
  pin 
  was 
  small 
  ; 
  and 
  one 
  difficulty 
  to 
  be 
  

   obviated 
  was 
  the 
  heating 
  and 
  even 
  fusion 
  of 
  the 
  platinum 
  when 
  the 
  

   circuit 
  was 
  completed. 
  This 
  was 
  met 
  by 
  using 
  the 
  small-sized 
  cells 
  men- 
  

   tioned 
  above, 
  and 
  employing 
  a 
  fine 
  copper 
  wire 
  (No. 
  26) 
  round 
  the 
  

   electromagnet. 
  The 
  very 
  slight 
  " 
  strength 
  of 
  current," 
  or 
  minute 
  

   (l 
  quantity," 
  required 
  for 
  the 
  illumination 
  of 
  vacuum-tubes 
  made 
  it 
  pos- 
  

   sible 
  so 
  to 
  reduce 
  the 
  surface 
  of 
  the 
  battery-cells 
  and 
  the 
  diameter 
  of 
  

   wire 
  as 
  to 
  render 
  the 
  overheating 
  in 
  a 
  great 
  measure 
  avoidable. 
  This 
  

   reduction 
  of 
  dimensions, 
  however, 
  is 
  limited, 
  first, 
  by 
  the 
  amount 
  of 
  mag- 
  

   netism 
  required 
  to 
  keep 
  up 
  the 
  vibrations, 
  and, 
  secondly, 
  by 
  the 
  diameter 
  

   of 
  the 
  tubes 
  used 
  for 
  the 
  experiments 
  ; 
  for 
  it 
  is 
  obvious 
  that, 
  since 
  wire 
  

   and 
  tube 
  both 
  form 
  parts 
  of 
  the 
  same 
  circuit, 
  in 
  order 
  to 
  produce 
  an 
  

   equal 
  illumination 
  (other 
  things 
  being 
  the 
  same), 
  we 
  must 
  for 
  a 
  tube 
  of 
  

   large 
  diameter 
  use 
  a 
  thicker 
  wire 
  than 
  would 
  be 
  necessary 
  for 
  one 
  of 
  

   small 
  diameter. 
  

  

  "With 
  a 
  contact-breaker 
  of 
  this 
  kind 
  in 
  good 
  action, 
  several 
  phenomena 
  

   were 
  noticeable 
  ; 
  but 
  first 
  and 
  foremost 
  was 
  the 
  fact 
  that, 
  in 
  a 
  large 
  

   number 
  of 
  tubes 
  (especially 
  hydrocarbons), 
  the 
  striae, 
  instead 
  of 
  being 
  

   sharp 
  and 
  flaky 
  in 
  form, 
  irregular 
  in 
  distribution, 
  and 
  fluttering 
  in 
  position, 
  

   were 
  soft 
  and 
  rounded 
  in 
  outline, 
  equidistant 
  in 
  their 
  intervals, 
  and 
  steady 
  

   in 
  proportion 
  to 
  the 
  regularity 
  of 
  the 
  contact-breaker. 
  These 
  results 
  are, 
  

   I 
  think, 
  attributable 
  more 
  to 
  the 
  regularity 
  than 
  to 
  the 
  rapidity 
  of 
  the 
  

   vibrations. 
  And 
  this 
  view 
  is 
  supported 
  by 
  the 
  fact 
  that, 
  although 
  the 
  

   contact-breaker 
  may 
  change 
  its 
  note 
  (as 
  occasionally 
  happens), 
  and 
  in 
  so 
  

   doing 
  may 
  cause 
  a 
  temporary 
  disturbance 
  in 
  the 
  stratification, 
  yet 
  the 
  

   new 
  note 
  may 
  produce 
  as 
  steady 
  a 
  set 
  of 
  striae 
  as 
  the 
  first 
  : 
  and 
  not 
  only 
  

   so, 
  but 
  frequently 
  there 
  is 
  heard, 
  simultaneously 
  with 
  a 
  pure 
  note 
  from 
  

   the 
  vibrator, 
  a 
  strident 
  sound, 
  indicating 
  that 
  contacts 
  of 
  two 
  separate 
  

   periods 
  are 
  being 
  made 
  ; 
  and 
  yet, 
  when 
  the 
  strident 
  sound 
  is 
  regular, 
  the 
  

   striae 
  are 
  steady. 
  On 
  the 
  other 
  hand, 
  to 
  any 
  sudden 
  alteration 
  in 
  the 
  

   action 
  of 
  the 
  break 
  (generally 
  implied 
  by 
  an 
  alteration 
  in 
  the 
  sound) 
  there 
  

   always 
  corresponds 
  an 
  alteration 
  in 
  the 
  striae. 
  

  

  It 
  is 
  difficult 
  to 
  describe 
  the 
  extreme 
  delicacy 
  in 
  action 
  of 
  this 
  kind 
  of 
  

   contact-breaker, 
  or 
  " 
  high 
  break," 
  as 
  it 
  may 
  be 
  called. 
  The 
  turning 
  

   through 
  2° 
  or 
  3° 
  of 
  a 
  screw, 
  whose 
  complete 
  revolution 
  raises 
  or 
  lowers 
  

   the 
  platinum 
  pin 
  through 
  -025 
  of 
  an 
  inch, 
  is 
  sufficient 
  to 
  produce 
  or 
  to 
  

   annihilate 
  the 
  entire 
  phenomenon. 
  A 
  similar 
  turn 
  in 
  a 
  screw 
  forming 
  

   one 
  foot 
  of 
  the 
  pedestal 
  of 
  the 
  break 
  is 
  enough 
  to 
  adjust 
  or 
  regulate 
  the 
  

   striae 
  ; 
  and 
  a 
  slight 
  pressure 
  of 
  the 
  finger 
  on 
  the 
  centre 
  of 
  the 
  mahogany 
  

  

  