﻿The 
  Echelon 
  Spectroscope. 
  371 
  

  

  viscosity 
  arising 
  from 
  the 
  rigidity 
  belonging 
  to 
  the 
  evenly 
  

   mixed 
  ions 
  becomes 
  o£ 
  paramount 
  importance 
  because 
  o£ 
  the 
  

   greatly 
  increased 
  time 
  of 
  relaxation 
  for 
  large 
  ions. 
  The 
  theory 
  

   of 
  the 
  large 
  ion 
  without 
  nucleus 
  leads 
  to 
  (27), 
  an 
  equation 
  

   connecting 
  the 
  mobility 
  of 
  this 
  kind 
  of 
  large 
  ion 
  with 
  con- 
  

   centration 
  aod 
  temperature. 
  This 
  is 
  verified 
  in 
  Tables 
  IV. 
  

   and 
  y. 
  by 
  means 
  of 
  the 
  experiments 
  of 
  Moreau 
  on 
  the 
  slow 
  

   ions 
  formed 
  by 
  spraying 
  solutions 
  into 
  flames 
  and 
  cooling 
  the 
  

   resultino- 
  o-aseous 
  mixture. 
  For 
  the 
  laro;e 
  ion 
  of 
  Lano-evin, 
  

   on 
  the 
  supposition 
  that 
  it 
  has 
  a 
  nucleus 
  of 
  water, 
  equation 
  

   (29) 
  is 
  worked 
  out 
  to 
  show 
  the 
  connexion 
  of 
  mobility 
  with 
  

   concentration 
  of 
  the 
  ions, 
  density 
  of 
  the 
  air, 
  humidity 
  and 
  

   temperature. 
  This 
  shows 
  general 
  agreement 
  with 
  the 
  results 
  

   of 
  Pollock 
  as 
  to 
  the 
  effect 
  of 
  humidity 
  on 
  the 
  mobility 
  of 
  the 
  

   large 
  ion 
  of 
  Langevin. 
  Experimental 
  data 
  are 
  lacking 
  to 
  

   test 
  it 
  otherwise. 
  To 
  account 
  for 
  the 
  permanence 
  of 
  this 
  

   large 
  ion 
  it 
  is 
  pointed 
  out 
  that 
  the 
  ionizing 
  power 
  of 
  water 
  

   tends 
  to 
  keep 
  it 
  intact. 
  Certain 
  objections 
  are 
  raised 
  to 
  the 
  

   theory 
  of 
  J. 
  J. 
  Thomson 
  and 
  Langevin 
  to 
  account 
  for 
  cloudy 
  

   condensation 
  of 
  HoO 
  vapour 
  on 
  small 
  ions 
  at 
  fourfold 
  

   saturation. 
  

  

  During 
  the 
  working 
  out 
  of 
  the 
  foregoing 
  I 
  have 
  had 
  the 
  

   advantage 
  of 
  correspondence 
  with 
  Prof. 
  Pollock 
  while 
  

   engaged 
  in 
  his 
  experimental 
  inquiries 
  on 
  large 
  ions. 
  

  

  Melbourne, 
  June, 
  1909. 
  

  

  XLIV. 
  The 
  Echelon 
  Spectroscope^ 
  its 
  Secondary 
  Action, 
  and 
  

   the 
  Structure 
  of 
  the 
  Green 
  Mercury 
  Line. 
  By 
  Herbert 
  

   Staxsfield, 
  D.Sc.y 
  Demonstrator 
  in 
  Physics, 
  Manchester 
  

   University*. 
  

  

  Thesis 
  approved 
  for 
  the 
  Degree 
  of 
  Doctor 
  of 
  Science 
  in 
  the 
  

   University 
  of 
  London 
  f. 
  

  

  [Plates 
  X.-XII.] 
  

   Part 
  I. 
  — 
  The 
  Echelon 
  Spectroscope. 
  

  

  The 
  Echelon 
  and 
  its 
  Mounting. 
  

  

  THE 
  echelon 
  spectroscope 
  described 
  in 
  this 
  paper 
  was 
  

   constructed 
  by 
  Messrs. 
  Adnm 
  Hilger 
  for 
  Professor 
  

   Schuster, 
  a 
  modification, 
  which 
  has 
  proved 
  to 
  be 
  very 
  

   valuable, 
  being 
  made 
  in 
  the 
  usual 
  design. 
  A 
  front 
  elevation, 
  

  

  * 
  Communicated 
  by 
  the 
  Physical 
  Society 
  : 
  read 
  June 
  11, 
  1909. 
  

  

  + 
  The 
  following 
  alterations 
  have 
  been 
  made 
  : 
  — 
  Equations 
  2, 
  3, 
  4, 
  9, 
  9 
  a, 
  

   and 
  the 
  section 
  on 
  the 
  spectrum 
  given 
  by 
  a 
  hot 
  lamp 
  have 
  been 
  added 
  j 
  

   also 
  the 
  faint 
  lines 
  previously 
  described 
  as 
  doubtful 
  are 
  shown 
  to 
  have 
  

   their 
  origin 
  in 
  the 
  echelon. 
  

  

  