﻿772 
  Mr. 
  T. 
  J. 
  liichmond 
  on 
  the 
  Formation 
  of 
  Strice 
  

  

  which 
  the 
  value 
  of 
  the 
  half- 
  wavelength 
  can 
  be 
  satisfactorily 
  

   obtained. 
  A 
  similar 
  phenomenon 
  was 
  observed 
  in 
  the 
  

   following 
  experiments 
  especially 
  in 
  the 
  wide 
  tubes. 
  

  

  Preliminary 
  Experiments. 
  Variatioyi 
  of 
  figures 
  with 
  

   diameter 
  of 
  the 
  tubes. 
  

  

  The 
  first 
  experiments 
  were 
  made 
  with 
  a 
  large 
  Wimshurst 
  

   machine 
  giving 
  an 
  intense 
  spark 
  about 
  two 
  centimetres 
  long. 
  

   A 
  length 
  of 
  glass 
  tubing 
  was 
  taken 
  and 
  carefully 
  cleaned 
  by 
  

   means 
  of 
  a 
  cotton-wool 
  plug, 
  and 
  dried. 
  A 
  small 
  quantity 
  of 
  

   carefully 
  dried 
  lycopodium 
  was 
  then 
  poured 
  into 
  the 
  tube, 
  

   the 
  latter 
  being 
  shaken 
  in 
  order 
  to 
  get 
  the 
  particles 
  of 
  powder 
  

   as 
  evenly 
  distributed 
  in 
  the 
  tube 
  in 
  the 
  form 
  of 
  a 
  cloud 
  as 
  

   possible. 
  The 
  powder 
  was 
  then 
  allowed 
  to 
  settle, 
  and 
  by 
  

   gently 
  tapping 
  the 
  tube 
  when 
  horizontal 
  the 
  powder 
  was 
  

   obtained 
  as 
  a 
  practically 
  uniform 
  line 
  along 
  the 
  tube, 
  which 
  

   was 
  now 
  placed 
  on 
  supports 
  with 
  one 
  end 
  near 
  the 
  spark-gap 
  

   of 
  the 
  machine 
  and 
  perpendicular 
  to 
  the 
  discharging-rods. 
  

   The 
  tube 
  was 
  then 
  rotated 
  very 
  carefully 
  about 
  its 
  axis 
  until 
  

   the 
  line 
  of 
  powder 
  was 
  just 
  on 
  the 
  point 
  of 
  slipping 
  down 
  the 
  

   side 
  of 
  the 
  tube. 
  Under 
  these 
  conditions, 
  one 
  or 
  two 
  sparks 
  

   usually 
  sufficed 
  to 
  give 
  the 
  pattern 
  to 
  the 
  lycopodium, 
  but 
  

   continued 
  sparking 
  usually 
  added 
  to 
  the 
  distinctness 
  of 
  the 
  

   striation. 
  It 
  was 
  noticed 
  that 
  at 
  the 
  passage 
  of 
  each 
  spark 
  the 
  

   powder 
  jumped 
  and 
  fell 
  again 
  at 
  the 
  cessation 
  of 
  each 
  spark. 
  

  

  In 
  the 
  case 
  of 
  the 
  first 
  tube, 
  which 
  was 
  1*5 
  centimetres 
  

   radius, 
  the 
  figure 
  consisted 
  of 
  very 
  distinct 
  close 
  parallel 
  lines 
  

   filling 
  the 
  whole 
  length, 
  about 
  60 
  centimetres, 
  of 
  the 
  tube. 
  

   It 
  was 
  also 
  noticed 
  that 
  the 
  striae 
  were 
  curiously 
  bifurcated 
  

   at 
  places. 
  This 
  bifurcation 
  was 
  found 
  to 
  be 
  removed 
  almost 
  

   completely 
  by 
  continued 
  sparking. 
  In 
  this 
  and 
  other 
  wide 
  

   tubes, 
  the 
  first 
  effect 
  of 
  the 
  discharge 
  was 
  to 
  produce 
  a 
  series 
  

   of 
  very 
  fine 
  interlacing 
  lines 
  which 
  by 
  further 
  sparking 
  gave 
  

   the 
  final 
  system 
  of 
  parallel 
  lines 
  more 
  or 
  less 
  bifurcated. 
  

  

  A 
  second 
  tube 
  was 
  now 
  taken 
  about 
  one 
  centimetre 
  in 
  

   diameter, 
  and 
  using 
  the 
  same 
  spark 
  as 
  before 
  the 
  striation 
  of 
  

   lycopodium 
  was 
  obtained. 
  The 
  pattern 
  formed 
  in 
  this 
  case 
  

   differed 
  in 
  several 
  respects 
  from 
  that 
  of 
  the 
  previous 
  one. 
  In 
  

   the 
  first 
  place 
  the 
  distance 
  between 
  successive 
  striae 
  was 
  greater 
  

   than 
  in 
  the 
  case 
  of 
  the 
  larger 
  tube 
  ; 
  also 
  the 
  lines 
  were 
  of 
  

   the 
  nature 
  of 
  irregular 
  heaps 
  compared 
  with 
  the 
  remarkably 
  

   clear 
  regular 
  lines 
  obtained 
  in 
  the 
  first 
  case. 
  Another 
  

   difference 
  consisted 
  in 
  the 
  lack 
  of 
  bifurcation 
  of 
  the 
  lines 
  in 
  

   the 
  narrower 
  tube. 
  This 
  freedom 
  of 
  the 
  lines 
  from 
  bifur- 
  

   cation 
  in 
  the 
  narrower 
  tube 
  was 
  found 
  to 
  render 
  the 
  use 
  of 
  

   such 
  tubes 
  more 
  suitable 
  for 
  quantitative 
  experiments 
  than 
  

  

  