﻿458 
  Mr. 
  W. 
  Spottiswoode 
  on 
  Stratification 
  in 
  [June 
  10, 
  

  

  stand, 
  apparently 
  rigid, 
  or 
  even 
  on 
  the 
  table 
  on 
  which 
  the 
  contact-breaker 
  

   stands, 
  will 
  often 
  control 
  their 
  movements. 
  

  

  The 
  discharges 
  described 
  above 
  are 
  usually 
  (although 
  not 
  always) 
  those 
  

   produced 
  by 
  breaking 
  contact 
  ; 
  but 
  it 
  often 
  happens, 
  and 
  that 
  most 
  fre- 
  

   quently 
  when 
  the 
  strident 
  noise 
  is 
  heard, 
  that 
  the 
  current 
  produced 
  by 
  

   making 
  contact 
  is 
  strong 
  enough 
  to 
  cause 
  a 
  visible 
  discharge. 
  This 
  hap- 
  

   pens 
  with 
  the 
  ordinary 
  as 
  with, 
  the 
  high 
  break 
  ; 
  but 
  in 
  the 
  latter 
  case 
  the 
  

   double 
  current 
  presents 
  the 
  very 
  remarkable 
  peculiarity 
  that 
  the 
  striae 
  of 
  

   one 
  current 
  are 
  so 
  arranged 
  as 
  to 
  fit 
  exactly 
  into 
  the 
  intervals 
  of 
  the 
  

   other 
  ; 
  and, 
  further, 
  that 
  any 
  disturbance 
  affecting 
  the 
  column 
  of 
  striae 
  

   due 
  to 
  one 
  current 
  affects 
  similarly, 
  with 
  reference 
  to 
  absolute 
  space, 
  that 
  

   due 
  to 
  the 
  other, 
  so 
  that 
  the 
  double 
  column 
  moves, 
  if 
  at 
  all, 
  as 
  a 
  solid 
  or 
  

   elastic 
  mass. 
  And 
  this 
  fact 
  is 
  the 
  more 
  remarkable 
  if 
  we 
  consider, 
  as 
  is 
  

   easily 
  observed 
  in 
  a 
  revolving 
  mirror, 
  that 
  these 
  currents 
  are 
  alternate, 
  not 
  

   only 
  in 
  direction, 
  but 
  also 
  in 
  time, 
  and 
  that 
  no 
  one 
  of 
  them 
  is 
  produced 
  until 
  

   after 
  the 
  complete 
  extinction 
  of 
  its 
  predecessor. 
  And 
  it 
  is 
  also 
  worthy 
  

   of 
  note 
  that 
  this 
  association 
  of 
  striae 
  is 
  not 
  destroyed 
  even 
  when 
  the 
  two 
  

   currents 
  are 
  separated 
  more 
  or 
  less 
  towards 
  opposite 
  sides 
  of 
  the 
  tube 
  by 
  

   the 
  presence 
  of 
  a 
  magnetic 
  pole. 
  There 
  seems, 
  however, 
  to 
  be 
  a 
  tendency 
  

   in 
  that 
  case 
  for 
  the 
  striae 
  of 
  one 
  current 
  to 
  advance 
  upon 
  the 
  positions 
  

   occupied 
  by 
  those 
  of 
  the 
  reverse 
  current, 
  giving 
  the 
  whole 
  column 
  a 
  

   twisted 
  appearance. 
  But 
  as 
  there 
  is 
  no 
  trace, 
  so 
  far 
  as 
  my 
  observations 
  

   go, 
  of 
  this 
  association 
  of 
  alternate 
  discharges 
  when 
  produced 
  by 
  the 
  ordi- 
  

   nary 
  break, 
  we 
  seem 
  led 
  to 
  the 
  conclusion 
  that 
  a 
  stratified 
  discharge, 
  on 
  

   ceasing, 
  leaves 
  the 
  gas 
  so 
  distributed 
  as 
  to 
  favour, 
  during 
  a 
  very 
  short 
  

   interval 
  of 
  time, 
  a 
  similar 
  stratification 
  on 
  the 
  occurrence 
  of 
  another 
  dis- 
  

   charge, 
  whether 
  in 
  the 
  same 
  or 
  in 
  the 
  opposite 
  direction. 
  An 
  explana- 
  

   tion 
  of 
  the 
  fact 
  that 
  the 
  striae 
  of 
  alternate 
  discharges 
  occupy 
  alternate 
  

   and 
  not 
  similar 
  positions 
  is 
  not 
  obvious, 
  and 
  probably 
  demands 
  a 
  better 
  

   knowledge 
  of 
  the 
  nature 
  of 
  the 
  striae 
  than 
  we 
  possess 
  at 
  present. 
  

  

  The 
  column 
  of 
  striae 
  which 
  usually 
  occupy 
  a 
  large 
  part 
  of 
  the 
  tube 
  

   from 
  the 
  positive 
  towards 
  the 
  negative 
  terminal 
  have 
  hitherto 
  been 
  

   described 
  as 
  stationary, 
  except 
  as 
  disturbed 
  by 
  irregularities 
  of 
  the 
  break. 
  

   The 
  column 
  is, 
  however, 
  frequently 
  susceptible 
  of 
  a 
  general 
  motion 
  or 
  

   " 
  flow," 
  either 
  from 
  or 
  towards 
  the 
  positive 
  pole, 
  say 
  a 
  forward 
  or 
  back- 
  

   ward 
  flow. 
  A 
  similar 
  phenomenon 
  was 
  observed 
  by 
  Mr. 
  Gassiot 
  in 
  some 
  

   tubes 
  with 
  his 
  large 
  battery 
  ; 
  but 
  I 
  am 
  not 
  acquainted 
  with 
  the 
  exact 
  cir- 
  

   cumstances 
  under 
  which 
  it 
  was 
  produced. 
  This 
  flow 
  may 
  be 
  controlled, 
  

   both 
  in 
  velocity 
  and 
  in 
  direction, 
  by 
  resistance 
  introduced 
  into 
  the 
  cir- 
  

   cuit, 
  or 
  by 
  placing 
  the 
  tube 
  in 
  a 
  magnetic 
  field. 
  The 
  resistance 
  may 
  be 
  

   introduced 
  in 
  either 
  the 
  primary 
  or 
  the 
  secondary 
  circuit. 
  For 
  the 
  former 
  

   arrangement 
  I 
  have 
  successfully 
  employed 
  a 
  set 
  of 
  resistance-coils 
  sup- 
  

   plemented 
  by 
  a 
  rheostat. 
  For 
  the 
  secondary 
  current, 
  as 
  well 
  as 
  for 
  the 
  

   Holtz 
  machine, 
  I 
  have 
  used 
  an 
  instrument 
  devised 
  and 
  constructed 
  by 
  my 
  

  

  