﻿1875.] 
  Electrical 
  Discharges 
  through 
  Rarefied 
  Gases. 
  461 
  

  

  tion, 
  the 
  effects 
  with 
  the 
  Holtz 
  machine 
  were 
  very 
  striking 
  : 
  the 
  striae, 
  

   with 
  steady 
  revolution 
  of 
  the 
  machine, 
  became 
  fixed 
  in 
  position 
  and 
  well 
  

   defined. 
  This 
  tube, 
  some 
  carbonic-acid-gas 
  tubes, 
  and 
  one 
  or 
  two 
  others, 
  

   generally 
  containing 
  acid 
  residua, 
  form 
  a 
  class 
  in 
  which 
  the 
  action 
  of 
  the 
  

   machine 
  more 
  nearly 
  approaches 
  that 
  of 
  Mr. 
  Gassiot's 
  battery 
  than 
  in 
  any 
  

   others. 
  The 
  striae 
  thus 
  formed 
  were 
  not 
  easily 
  brought 
  into 
  a 
  state 
  of 
  

   flow 
  ; 
  but 
  an 
  increase 
  in 
  the 
  rapidity 
  of 
  the 
  machine, 
  or 
  a 
  diminution 
  of 
  

   resistance, 
  increased 
  the 
  number 
  of 
  the 
  striae. 
  As 
  the 
  rapidity 
  was 
  aug- 
  

   mented, 
  the 
  striae 
  might 
  be 
  seen 
  pouring 
  themselves 
  out, 
  as 
  it 
  were, 
  from 
  

   the 
  positive 
  pole 
  ; 
  the 
  length 
  of 
  the 
  column 
  was 
  slightly 
  increased, 
  but 
  by 
  

   no 
  means 
  in 
  proportion 
  to 
  the 
  number 
  of 
  striae. 
  

  

  One 
  modification 
  of 
  this 
  effect, 
  although 
  almost 
  fantastic 
  in 
  its 
  appear- 
  

   ance, 
  seems 
  to 
  deserve 
  a 
  special 
  notice. 
  It 
  is 
  well 
  known 
  that 
  if 
  a 
  suf- 
  

   ficient 
  interval 
  of 
  air 
  be 
  thrown 
  into 
  the 
  circuit 
  all 
  trace 
  of 
  stratification 
  

   disappears, 
  and 
  at 
  the 
  same 
  time 
  the 
  dark 
  interval 
  between 
  the 
  positive 
  

   and 
  negative 
  parts 
  and 
  the 
  negative 
  halo 
  itself 
  are 
  obliterated. 
  If, 
  how- 
  

   ever, 
  the 
  interval 
  of 
  air 
  be 
  very 
  small, 
  the 
  two 
  kinds 
  of 
  discharge 
  may 
  be 
  

   seen 
  coexisting 
  ; 
  a 
  narrow 
  column 
  of 
  the 
  continuous 
  discharge 
  extends 
  

   along 
  the 
  tube, 
  and 
  on 
  it 
  the 
  striae 
  appear 
  to 
  be 
  strung. 
  These 
  effects 
  

   are 
  easily 
  produced 
  by 
  slightly 
  lowering 
  one 
  of 
  the 
  vertical 
  conductors 
  of 
  

   the 
  machine 
  ; 
  and 
  perhaps 
  the 
  best 
  effects 
  are 
  shown 
  if 
  the 
  conductor 
  on 
  

   the 
  side 
  connected 
  with 
  the 
  positive 
  terminal 
  of 
  the 
  tube 
  is 
  lowered. 
  

   When 
  this 
  is 
  done 
  the 
  striae 
  occupying 
  the 
  portion 
  nearest 
  to 
  that 
  ter- 
  

   minal 
  become 
  widely 
  separated 
  at 
  unequal 
  and 
  varying 
  intervals 
  ; 
  they 
  

   appear 
  to 
  oscillate 
  along 
  the 
  tube 
  with 
  independent 
  motions, 
  as 
  if 
  attached 
  

   to 
  an 
  elastic 
  string 
  which 
  at 
  each 
  instant 
  is 
  unequally 
  stretched 
  at 
  its 
  

   various 
  parts. 
  The 
  portion 
  of 
  the 
  column 
  so 
  affected 
  varies 
  with 
  the 
  

   length 
  of 
  the 
  interval 
  of 
  air 
  ; 
  and 
  when, 
  for 
  instance, 
  that 
  portion 
  amounts 
  

   to 
  two 
  thirds 
  of 
  the 
  entire 
  length, 
  the 
  striae 
  in 
  the 
  remaining 
  third 
  appear 
  

   crowded 
  together. 
  As 
  the 
  interval 
  of 
  air 
  is 
  further 
  increased 
  more 
  striae 
  

   become 
  disturbed, 
  the 
  continuous 
  discharge 
  becomes 
  wider 
  and 
  more 
  pro- 
  

   minent, 
  and 
  ultimately 
  overpowers 
  and 
  obliterates 
  the 
  striae. 
  

  

  The 
  resistance-coil 
  used 
  for 
  the 
  secondary 
  current 
  or 
  the 
  machine 
  consists 
  

   of 
  a 
  hollow 
  glass 
  spiral, 
  AAA 
  (fig. 
  3), 
  having 
  a 
  length 
  of 
  about 
  50 
  inches 
  

   and 
  an 
  internal 
  diameter 
  of 
  ^ 
  of 
  an 
  inch. 
  At 
  the 
  head 
  is 
  a 
  small 
  glass 
  

   bulb 
  B, 
  having 
  an 
  opening 
  at 
  the 
  top, 
  which 
  is 
  closed 
  by 
  a 
  glass 
  stopper. 
  A 
  

   platinum 
  wire, 
  N, 
  connected 
  with 
  one 
  of 
  the 
  terminals, 
  H, 
  dips 
  to 
  the 
  

   bottom 
  of 
  the 
  bulb 
  B, 
  which 
  is 
  partially 
  filled 
  with 
  sulphuric 
  acid. 
  C 
  is 
  

   a 
  small 
  glass 
  bulb 
  containing 
  mercury, 
  and 
  is 
  connected 
  with 
  the 
  lower 
  

   end 
  of 
  the 
  spiral 
  by 
  a 
  flexible 
  tube, 
  D. 
  The 
  height 
  of 
  this 
  bulb 
  can 
  be 
  

   regulated 
  by 
  means 
  of 
  the 
  slide 
  F, 
  which 
  moves 
  on 
  the 
  steel 
  rod 
  E. 
  P 
  

   is 
  a 
  small 
  platinum 
  wire 
  fused 
  into 
  the 
  interior 
  of 
  the 
  bulb 
  Gr, 
  and 
  is 
  in 
  

   connexion 
  with 
  the 
  other 
  terminal, 
  H. 
  

  

  If 
  the 
  bulb 
  C 
  be 
  placed 
  in 
  any 
  position, 
  the 
  mercury 
  will 
  rise 
  in 
  the 
  

   spiral 
  to 
  the 
  same 
  level 
  as 
  that 
  in 
  the 
  bulb. 
  The 
  mercury 
  will 
  act 
  

  

  