﻿Bigl 
  i- 
  Frequency 
  Spectra 
  of 
  the 
  Elements. 
  1029 
  

  

  This 
  gives 
  d'= 
  2-814X10- 
  8 
  and 
  ^=8*454x10-8 
  cm. 
  

   It 
  is 
  seen 
  that 
  the 
  determination 
  of 
  wave-length 
  depends 
  

  

  on 
  e 
  3 
  , 
  so 
  that 
  the 
  effect 
  of 
  uncertainty 
  in 
  the 
  value 
  of 
  

   this 
  quantity 
  will 
  not 
  be 
  serious. 
  Lack 
  of 
  homogeneity 
  in 
  

   the 
  crystal 
  is 
  a 
  more 
  likely 
  source 
  of 
  error, 
  as 
  minute 
  

   inclusions 
  of 
  water 
  would 
  make 
  the 
  true 
  density 
  greater 
  

   than 
  that 
  found 
  experimentally. 
  

  

  Twelve 
  elements 
  have 
  so 
  far 
  been 
  examined. 
  The 
  ten 
  

   given 
  in 
  Table 
  I. 
  were 
  chosen 
  as 
  forming 
  a 
  continuous 
  

   series 
  with 
  only 
  one 
  gap. 
  It 
  was 
  hoped 
  in 
  this 
  way 
  to 
  

   bring 
  out 
  clearly 
  any 
  systematic 
  results. 
  The 
  inclusion 
  

   of 
  nickel 
  was 
  of 
  special 
  interest 
  owing 
  to 
  its 
  anomalous 
  

   position 
  in 
  the 
  periodic 
  system. 
  Radiations 
  from 
  these 
  

   substances 
  are 
  readily 
  excited, 
  and 
  the 
  large 
  angles 
  of 
  

   reflexion 
  make 
  it 
  easy 
  to 
  measure 
  the 
  wave-lengths 
  with 
  

   accuracy. 
  Calcium 
  alone 
  gave 
  any 
  trouble. 
  In 
  this 
  case, 
  

   owing 
  to 
  the 
  high 
  absorption 
  coefficient 
  of 
  the 
  principal 
  

   radiation 
  — 
  about 
  1200 
  cm. 
  -1 
  in 
  aluminium 
  — 
  the 
  X-ray 
  tube 
  

   was 
  provided 
  with 
  a 
  window 
  of 
  goldbeaters' 
  skin 
  and 
  the 
  air 
  

   between 
  the 
  crystal 
  and 
  the 
  photographic 
  plate 
  displaced 
  by 
  

   hydrogen. 
  The 
  layer 
  of 
  lime 
  which 
  covered 
  the 
  surface 
  of 
  

   the 
  metal 
  gave 
  off 
  such 
  a 
  quantity 
  of 
  gas 
  that 
  the 
  X 
  rays 
  

   could 
  only 
  be 
  excited 
  for 
  a 
  second 
  or 
  two 
  at 
  a 
  time. 
  Brass 
  was 
  

   substituted 
  for 
  zinc 
  to 
  avoid 
  volatilization 
  by 
  the 
  intense 
  heat 
  

   generated 
  at 
  the 
  point 
  struck 
  by 
  the 
  cathode 
  rays. 
  Ferro- 
  

   vanadium 
  (35 
  per 
  cent. 
  V) 
  and 
  ferro-titanium 
  (23 
  per 
  cent. 
  Ti), 
  

   for 
  which 
  I 
  am 
  indebted 
  to 
  the 
  International 
  Vanadium 
  Co., 
  

   proved 
  convenient 
  substitutes 
  for 
  the 
  pure 
  elements, 
  which 
  

   are 
  not 
  easily 
  obtained 
  in 
  the 
  solid 
  form. 
  

  

  Plate 
  XXIII. 
  shows 
  the 
  spectra 
  in 
  the 
  third 
  order 
  placed 
  

   approximately 
  in 
  register. 
  Those 
  parts 
  of 
  the 
  photographs 
  

   which 
  represent 
  the 
  same 
  angle 
  of 
  reflexion 
  are 
  in 
  the 
  same 
  

   vertical 
  line. 
  The 
  actual 
  angles 
  can 
  be 
  taken 
  from 
  Table 
  I. 
  

   It 
  is 
  to 
  be 
  seen 
  that 
  the 
  spectrum 
  of 
  each 
  element 
  consists 
  of 
  

   two 
  lines. 
  Of 
  these 
  the 
  stronger 
  has 
  been 
  called 
  a 
  in 
  the 
  

   table, 
  and 
  the 
  weaker 
  j3. 
  The 
  lines 
  found 
  on 
  any 
  of 
  the 
  plates 
  

   besides 
  a. 
  and 
  ft 
  were 
  almost 
  certainly 
  all 
  due 
  to 
  impurities. 
  

   Thus 
  in 
  both 
  the 
  third 
  and 
  second 
  order 
  the 
  cobalt 
  spectrum 
  

   shows 
  Ni 
  a 
  very 
  strongly 
  anl 
  Fe 
  ol 
  faintly. 
  In 
  the 
  third 
  order 
  

   the 
  nickel 
  spectrum 
  shows 
  Mn« 
  2 
  faintly. 
  The 
  brass 
  spectra 
  

   naturally 
  show 
  a 
  and 
  /3 
  both 
  of 
  Cu 
  and 
  of 
  Zn, 
  but 
  Zn/3 
  2 
  has 
  

   not 
  yet 
  been 
  found. 
  In 
  the 
  second 
  order 
  the 
  ferro-vanadium 
  

   and 
  ferro-titanium 
  spectra 
  show 
  very 
  intense 
  third-order 
  

   Fe 
  lines, 
  and 
  the 
  former 
  also 
  shows 
  Cu 
  a 
  3 
  faintly. 
  The 
  Co 
  

   contained 
  Ni 
  and 
  0*8 
  per 
  cent. 
  Fe, 
  the 
  Ni 
  2'2 
  per 
  cent. 
  Mn, 
  

  

  