﻿in 
  a 
  Dust-Tuhe 
  by 
  an 
  Electric. 
  Discharge. 
  

  

  773 
  

  

  wider 
  ones 
  on 
  account 
  o£ 
  the 
  greater 
  certainty 
  as 
  to 
  the 
  

   number 
  o£ 
  lines 
  contained 
  in 
  a 
  certain 
  length 
  of 
  the 
  tube. 
  

  

  The 
  difference 
  in 
  the 
  distances 
  between 
  the 
  lines 
  in 
  the 
  above 
  

   two 
  cases 
  suoo-ested 
  the 
  investiojation 
  o£ 
  the 
  relation 
  between 
  

   the 
  striae-distance 
  — 
  i. 
  e., 
  distance 
  between 
  successive 
  striae 
  — 
  

   and 
  the 
  diameter 
  o£ 
  the 
  tube 
  in 
  which 
  the 
  pattern 
  was 
  formed. 
  

   A 
  set 
  o£ 
  five 
  tubes 
  ranging 
  in 
  diameter 
  from 
  1 
  centimetre 
  to 
  

   4*6 
  centimetres 
  was 
  taken, 
  and 
  using 
  the 
  same 
  spark 
  in 
  all 
  

   cases 
  the 
  figure 
  assumed 
  by 
  the 
  lycopodium 
  was 
  observed 
  and 
  

   measured, 
  care 
  having 
  been 
  taken 
  to 
  ensure 
  the 
  cleanness 
  

   and 
  dryness 
  of 
  the 
  tubes. 
  This 
  somewhat 
  rough 
  set 
  of 
  

   readinos 
  indicated 
  a 
  turnino- 
  value 
  in 
  the 
  variation 
  under 
  

   investigation, 
  as 
  shown 
  in 
  figures 
  given 
  in 
  Table 
  I. 
  and 
  

   graphically 
  in 
  Curve 
  I. 
  fig. 
  1 
  (p. 
  775). 
  

  

  Table 
  I. 
  — 
  Variation 
  of 
  figures 
  with 
  diameter 
  of 
  tube. 
  

  

  Diameter 
  of 
  tube. 
  

  

  Striae-distance. 
  

  

  •9 
  cm. 
  

  

  1 
  

   •77 
  mm. 
  

  

  I 
  1-0 
  „ 
  

  

  •77 
  „ 
  

  

  1-G 
  „ 
  

  

  1-00 
  „ 
  

  

  2-G 
  „ 
  

  

  ■77 
  ,, 
  

  

  4-6 
  „ 
  

  

  •55 
  „ 
  

  

  From 
  these 
  figures 
  it 
  appears 
  that 
  the 
  striae-distance 
  has 
  a 
  

   maximum 
  value, 
  viz. 
  I'OO 
  mm. 
  in 
  the 
  1*6 
  cm. 
  tube. 
  In 
  con- 
  

   firmation 
  of 
  the 
  existence 
  of 
  this 
  turning 
  value 
  a 
  second 
  set 
  

   of 
  readings 
  was 
  taken. 
  The 
  tubes 
  having 
  been 
  carefully 
  

   cleaned 
  and 
  dried 
  and 
  the 
  pattern 
  in 
  each 
  case 
  obtained 
  as 
  

   clear 
  as 
  possible, 
  a 
  vernier 
  microscope 
  was 
  used 
  to 
  measure 
  the 
  

   intervals. 
  The 
  tubes 
  were 
  in 
  turn 
  laid 
  on 
  the 
  stage 
  of 
  the 
  micro- 
  

   scope, 
  a 
  piece 
  of 
  black 
  paper 
  being 
  placed 
  underneath 
  to 
  

   facilitate 
  the 
  reading 
  of 
  the 
  microscope. 
  By 
  this 
  means 
  the 
  

   figure 
  as 
  viewed 
  through 
  the 
  microscope 
  appeared 
  very 
  

   distinct 
  and 
  the 
  separate 
  lines 
  could 
  be 
  counted 
  with 
  ease. 
  

   The 
  striae-distance 
  was 
  obtained 
  by 
  observing 
  the 
  distance 
  

   through 
  which 
  the 
  microscope 
  travelled 
  in 
  order 
  that 
  say 
  

   10 
  lines 
  should 
  pass 
  across 
  the 
  intersection 
  of 
  the 
  cross-wires 
  

   of 
  the 
  eyepiece. 
  It 
  was 
  noticed 
  that 
  some 
  uncertainty 
  existed 
  

   in 
  some 
  cases 
  as 
  to 
  whether 
  one 
  or 
  two 
  lines 
  had 
  passed 
  across 
  

   the 
  intersection 
  of 
  the 
  cross-wires 
  owing 
  to 
  the 
  bifurcation 
  

   of 
  the 
  lines 
  as 
  previously 
  mentioned. 
  This 
  most 
  probably 
  

   explains 
  the 
  several 
  high 
  values 
  obtained 
  in 
  the 
  figures 
  for 
  

   the 
  4*4 
  centimetres 
  tube 
  shown 
  in 
  Table 
  II. 
  There 
  were 
  

  

  