﻿776 
  Mr. 
  T. 
  J. 
  Richmond 
  on 
  tJie 
  Formation 
  of 
  Striw 
  

  

  powder 
  absolutely 
  unmoved. 
  The 
  pattern 
  was 
  then 
  destroyed 
  

   by 
  knocking 
  the 
  tube 
  and 
  no 
  amount 
  of 
  sparking 
  would 
  

   cause 
  the 
  striation 
  o£ 
  the 
  powder. 
  This 
  shows 
  that 
  the 
  

   formation 
  of 
  the 
  striation 
  is 
  due 
  to 
  aerial 
  motions. 
  

  

  Variation 
  of 
  figures 
  with 
  nature 
  of 
  powder. 
  

  

  The 
  effect 
  of 
  the 
  nature 
  of 
  the 
  powder 
  was 
  now 
  looked 
  for. 
  

   Using 
  the 
  same 
  electrical 
  arrangements 
  as 
  above 
  in 
  all 
  the 
  

   cases 
  striae 
  were 
  obtained 
  in 
  tubes 
  about 
  1 
  cm. 
  in 
  diameter 
  

   with 
  various 
  powders, 
  the 
  figures 
  in 
  Table 
  lY. 
  were 
  

   obtained. 
  

  

  Table 
  IV. 
  — 
  Variation 
  of 
  striation 
  with 
  powder. 
  

  

  1 
  

   Name 
  of 
  Powder 
  used. 
  

  

  Lycopodium 
  

  

  Striae-distance. 
  , 
  Natureof 
  Powder 
  : 
  form 
  and 
  size. 
  

  

  •84 
  mm. 
  Spheroidal 
  particles. 
  

  

  •73 
  „ 
  Eound 
  particles 
  of 
  smaller 
  size. 
  

  

  •53 
  „ 
  

  

  •81 
  „ 
  Spheroidal 
  particles. 
  

  

  •70 
  ,, 
  Round 
  particles. 
  

  

  — 
  Very 
  light 
  & 
  verj- 
  small 
  particles. 
  

   1"20 
  „ 
  Long 
  narrow 
  needles. 
  

   •52 
  „ 
  More 
  or 
  less 
  approaching 
  sphe- 
  

   roidal. 
  

   •70 
  „ 
  Irregular. 
  

  

  Ij^oror-Tjowder 
  , 
  

  

  1 
  Starch 
  

  

  Pepper 
  

  

  Boric 
  Acid 
  

  

  

  Powdered 
  Charcoal 
  

  

  Bath-Brick 
  

  

  Carbonate 
  of 
  Iron 
  

  

  From 
  these 
  figures 
  it 
  appears 
  that 
  the 
  nature 
  of 
  the 
  powder 
  

   has 
  some 
  influence 
  on 
  the 
  striae- 
  distance. 
  A 
  noteworthy 
  

   feature 
  of 
  these 
  figures 
  is 
  that 
  lycopodium 
  and 
  pepper 
  are 
  

   not 
  very 
  different 
  in 
  their 
  behaviour. 
  This 
  similarity 
  in 
  

   behaviour 
  of 
  pepper 
  and 
  lycopodium 
  is 
  perhaps 
  to 
  be 
  ex- 
  

   pected 
  since 
  the 
  two 
  powders 
  were 
  very 
  similar 
  in 
  form 
  and 
  

   size 
  of 
  grain. 
  

  

  For 
  figure 
  exhibiting 
  the 
  variation 
  of 
  the 
  striation 
  with 
  

   various 
  powders 
  see 
  fig. 
  II. 
  From 
  this 
  figure 
  it 
  is 
  observed 
  

   that 
  the 
  striations 
  in 
  case 
  of 
  lycopodium 
  and 
  pepper 
  are 
  very 
  

   similar 
  in 
  appearance. 
  It 
  is 
  also 
  evident 
  that 
  lycopodium 
  gives 
  

   the 
  most 
  definite 
  figures, 
  it 
  being 
  much 
  easier 
  to 
  measure 
  the 
  

   striae- 
  distance 
  in 
  this 
  case 
  than 
  in 
  case 
  of 
  starch 
  (c, 
  fig. 
  II.) 
  or 
  

   boric 
  acid 
  (e, 
  fig. 
  IE.). 
  

  

  A 
  factor 
  which 
  appeared 
  to 
  enter 
  largely 
  into 
  the 
  formation 
  

   of 
  a 
  distinct 
  figure 
  is 
  the 
  density 
  of 
  the 
  powder. 
  Thus 
  some 
  

   of 
  the 
  powders 
  seemed 
  too 
  light 
  to 
  give 
  a 
  clear 
  figure. 
  As 
  

   indicated 
  in 
  Table 
  IV., 
  no 
  striation 
  could 
  be 
  obtained 
  with 
  

   chromate 
  of 
  zinc, 
  the 
  particles, 
  which 
  were 
  very 
  fine, 
  being 
  

   caused 
  to 
  jump 
  at 
  each 
  spark, 
  but 
  at 
  the 
  cessation 
  of 
  a 
  spark 
  

  

  