﻿L 
  771 
  ] 
  

  

  LXXX. 
  On 
  the 
  Formation 
  of 
  Striae 
  in 
  a 
  Dust-Tuhe 
  hy 
  an 
  Elec- 
  

   tric 
  Discharge. 
  By 
  Thos. 
  Jas. 
  Richaio>s'D, 
  B,Sc. 
  (Lond.) 
  ; 
  

   Research 
  Student 
  at 
  University 
  College^ 
  Nottingham 
  *. 
  

  

  [Plates 
  XXIV.-XXVI.] 
  

  

  IN 
  1898 
  H. 
  V. 
  Gill, 
  S. 
  J., 
  in 
  a 
  paper 
  in 
  the 
  ' 
  American 
  

   Journal 
  of 
  Science/ 
  propounded 
  a 
  theory 
  to 
  account 
  for 
  

   the 
  striation 
  of 
  the 
  electric 
  discharge 
  in 
  vacuum-tubes. 
  In 
  

   this 
  paper 
  the 
  author 
  draws 
  attention 
  to 
  the 
  fact 
  that, 
  under 
  

   suitable 
  conditions, 
  lycopodium 
  powder 
  placed 
  in 
  a 
  glass 
  

   tube 
  arranges 
  itself 
  in 
  well-marked 
  stride 
  under 
  the 
  influence 
  

   of 
  an 
  electric 
  discharge. 
  This 
  suggested 
  the 
  following- 
  

   experiments 
  on 
  the 
  various 
  factors 
  involved 
  in 
  the 
  formation 
  

   of 
  the 
  strise, 
  the 
  special 
  object 
  being 
  to 
  ascertain 
  whether 
  the 
  

   frequency 
  of 
  the 
  electrical 
  oscillations 
  could 
  be 
  obtained 
  from 
  

   observation 
  of 
  the 
  striation 
  of 
  the 
  powder 
  under 
  their 
  

   influence. 
  

  

  The 
  nature 
  of 
  the 
  striation 
  might 
  conceivably 
  depend 
  on 
  

   the 
  nature 
  of 
  the 
  powder 
  used 
  ; 
  that 
  is 
  on 
  the 
  size 
  and 
  form 
  

   of 
  the 
  grains 
  ; 
  on 
  the 
  electrical 
  conditions 
  ; 
  and 
  on 
  the 
  

   dimensions 
  of 
  the 
  tube 
  containing 
  the 
  powder. 
  It 
  might 
  also 
  

   depend, 
  perhaps, 
  on 
  whether 
  the 
  further 
  end 
  of 
  the 
  tube 
  were 
  

   open 
  or 
  stopped. 
  All 
  these 
  questions 
  have 
  been 
  considered 
  

   in 
  the 
  following, 
  and 
  quantitative 
  experiments 
  were 
  made 
  in 
  

   which 
  the 
  frequency 
  and 
  wave-length 
  of 
  the 
  electrical 
  oscil- 
  

   lations 
  were 
  measured 
  by 
  means 
  of 
  Fleming's 
  Cymometer, 
  

   and 
  the 
  striation 
  in 
  each 
  case 
  observed 
  ; 
  and 
  although 
  no 
  

   definite 
  relation 
  between 
  the 
  frequency 
  of 
  the 
  electrical 
  

   oscillations 
  producing 
  a 
  certain 
  striation 
  and 
  the 
  distance 
  

   between 
  the 
  striae 
  was 
  detected, 
  some 
  results 
  were 
  obtained 
  

   which 
  appear 
  of 
  interest 
  and 
  worth 
  recording. 
  

  

  As 
  regards 
  the 
  effect 
  of 
  the 
  structure 
  of 
  the 
  powder, 
  it 
  is 
  

   to 
  be 
  observed 
  that 
  an 
  aggregation 
  of 
  spherical 
  particles 
  tends, 
  

   under 
  the 
  influence 
  of 
  fluid 
  motion, 
  to 
  arrange 
  itself 
  as 
  strise 
  

   across 
  the 
  direction 
  of 
  the 
  motion. 
  An 
  example 
  of 
  this 
  effect 
  

   is 
  afforded 
  by 
  the 
  well-known 
  method 
  due 
  to 
  Kundt 
  for 
  the 
  

   determination 
  of 
  the 
  velocity 
  of 
  sound. 
  When 
  the 
  note 
  is 
  

   first 
  elicited 
  from 
  the 
  sounding 
  rod, 
  the 
  lycopodium 
  forms 
  

   itself 
  into 
  a 
  series 
  of 
  fine 
  close 
  lines 
  along 
  which 
  a 
  series 
  of 
  

   nodes 
  and 
  antinodes 
  is 
  more 
  or 
  less 
  clearly 
  discernible, 
  but 
  

   these 
  nodes 
  are 
  not 
  at 
  first 
  sufficiently 
  clearly 
  defined 
  to 
  allow 
  

   an 
  accurate 
  value 
  of 
  the 
  half-wavelength 
  to 
  be 
  obtained, 
  and 
  

   it 
  requires 
  more 
  or 
  less 
  continued 
  stroking 
  of 
  the 
  rod 
  to 
  cause 
  

   the 
  lycopodium 
  to 
  assume 
  that 
  very 
  distinct 
  pattern 
  from 
  

  

  * 
  Communicated 
  by 
  Prof. 
  E. 
  II. 
  Pmrton. 
  

  

  