﻿460 
  Mr. 
  W, 
  Spottiswoode 
  on 
  Stratification 
  in 
  [June 
  10, 
  

  

  tionary 
  and 
  the 
  second 
  be 
  flowing 
  backwards 
  (i. 
  e. 
  from 
  — 
  to 
  + 
  ), 
  a 
  mag- 
  

   netic 
  pole 
  of 
  suitable 
  strength, 
  placed 
  at 
  the 
  distant 
  end 
  of 
  the 
  latter, 
  

   will 
  stop 
  its 
  flow, 
  and 
  the 
  whole 
  column 
  will 
  become 
  stationary 
  through- 
  

   out. 
  An 
  increase 
  in 
  the 
  strength 
  of 
  the 
  magnet, 
  or 
  a 
  nearer 
  approach 
  

   of 
  it 
  to 
  the 
  tube, 
  will 
  produce 
  a 
  general 
  forward 
  flow 
  of 
  the 
  column. 
  

  

  The 
  phenomena 
  of 
  the 
  flow, 
  as 
  well 
  as 
  others 
  of 
  not 
  less 
  interest, 
  are 
  

   capable 
  of 
  being 
  produced 
  with 
  the 
  Holtz 
  machine. 
  It 
  is 
  well 
  known 
  

   that 
  stratified 
  discharges, 
  similar 
  to 
  those 
  produced 
  by 
  an 
  induction-coil 
  

   working 
  with 
  an 
  ordinary 
  break, 
  may 
  be 
  produced 
  by 
  such 
  a 
  machine, 
  

   provided 
  that 
  it 
  be 
  furnished 
  with 
  the 
  usual 
  Leyden 
  jars, 
  and 
  a 
  high 
  

   resistance 
  (usually 
  a 
  piece 
  of 
  wetted 
  string) 
  be 
  interposed 
  in 
  the 
  circuit. 
  

   The 
  absence 
  of 
  either 
  of 
  these 
  conditions 
  was 
  supposed 
  to 
  destroy 
  the 
  

   striae 
  and 
  to 
  render 
  the 
  discharge 
  continuous. 
  Experiments 
  which 
  I 
  have 
  

   recently 
  made, 
  but 
  do 
  not 
  describe 
  on 
  the 
  present 
  occasion, 
  tend 
  in 
  part, 
  

   but 
  only 
  in 
  part, 
  to 
  confirm 
  this 
  view. 
  They 
  show 
  that 
  for 
  the 
  produc- 
  

   tion 
  of 
  striae 
  both 
  quantity 
  and 
  resistance 
  are 
  necessary, 
  that 
  the 
  dis- 
  

   charge 
  must 
  occupy 
  a 
  certain 
  short, 
  perhaps, 
  but 
  finite 
  time, 
  or, 
  as 
  

   it 
  may 
  also 
  be 
  expressed, 
  that 
  a 
  continuous 
  current 
  is 
  an 
  essential 
  

   element. 
  

  

  Now, 
  seeing 
  that 
  every 
  tube 
  must 
  offer 
  some 
  resistance, 
  and 
  also 
  that 
  

   by 
  adjusting 
  the 
  height 
  of 
  the 
  vertical 
  condensors 
  of 
  the 
  machine 
  (or 
  

   length 
  of 
  air-spark 
  interposed 
  in 
  the 
  circuit) 
  we 
  had 
  the 
  means 
  of 
  alter- 
  

   ing 
  the 
  quantity 
  in 
  the 
  discharge, 
  it 
  seemed 
  worth 
  while 
  to 
  try 
  whether, 
  

   by 
  a 
  suitable 
  adjustment 
  of 
  the 
  parts, 
  phenomena 
  similar 
  to 
  those 
  brought 
  

   out 
  by 
  the 
  coil 
  and 
  high 
  break 
  might 
  not 
  be 
  produced 
  by 
  the 
  machine. 
  

   And 
  this 
  proved 
  to 
  be 
  very 
  easy 
  of 
  attainment 
  in 
  tubes 
  which 
  had 
  been 
  

   successfully 
  used 
  by 
  the 
  coil 
  ; 
  and 
  not 
  only 
  so, 
  but 
  the 
  character 
  of 
  the 
  

   flow 
  therein 
  shown 
  confirmed 
  in 
  a 
  very 
  striking 
  and 
  simple 
  manner 
  the 
  

   effects 
  of 
  resistance 
  described 
  above. 
  

  

  The 
  connexions 
  being 
  made 
  in 
  the 
  usual 
  way, 
  and 
  no 
  air-spark 
  being 
  

   admitted 
  into 
  the 
  circuit, 
  a 
  vacuum-tube 
  of 
  carbonic 
  oxide, 
  about 
  60 
  

   centims. 
  in 
  length 
  and 
  4*5 
  centims. 
  in 
  outside 
  diameter, 
  gave, 
  when 
  the 
  

   plates 
  of 
  the 
  machine 
  revolved 
  at 
  about 
  six 
  times 
  per 
  second, 
  a 
  rather 
  

   confused 
  discharge. 
  As 
  the 
  speed 
  was 
  increased, 
  a 
  rapid 
  forward 
  flow 
  of 
  

   the 
  striae 
  was 
  readily 
  discerned 
  ; 
  and 
  on 
  a 
  still 
  further 
  increase 
  to 
  about 
  ten 
  

   revolutions 
  per 
  second, 
  the 
  flow, 
  first 
  in 
  one 
  part 
  and 
  then 
  throughout 
  

   nearly 
  the 
  whole 
  length 
  of 
  the 
  tube, 
  slackened 
  its 
  pace 
  and 
  stopped, 
  and 
  

   ultimately 
  reversed 
  its 
  motion. 
  An 
  increase 
  of 
  speed 
  is 
  equivalent 
  to 
  an 
  

   overcoming 
  or 
  a 
  diminution 
  of 
  resistance 
  in 
  the 
  circuit, 
  a 
  diminution 
  of 
  

   speed 
  to 
  an 
  augmentation 
  of 
  resistance. 
  Hence 
  the 
  phenomena 
  of 
  

   flow 
  produced 
  by 
  the 
  machine 
  agree 
  with 
  those 
  produced 
  by 
  the 
  coil. 
  

  

  It 
  is 
  unnecessary 
  to 
  detail 
  the 
  effects 
  obtained 
  with 
  many 
  other 
  tubes, 
  

   as 
  they 
  all 
  agreed 
  in 
  their 
  main 
  features. 
  

  

  In 
  a 
  sulphurous-acid 
  tube, 
  which 
  with 
  the 
  induction-coil 
  and 
  ordinary 
  

   break 
  gave 
  broad 
  flocculent 
  striae 
  but 
  unsteady 
  and 
  fluttering 
  in 
  posi- 
  

  

  