﻿Chemistry 
  and 
  Physics. 
  487 
  

  

  5. 
  Jl- 
  Ray 
  Band 
  Spectra. 
  — 
  Several 
  years 
  before 
  Laue 
  made 
  the 
  

   very 
  important 
  discovery 
  that 
  solid 
  crystals 
  may 
  be 
  used 
  as 
  three- 
  

   dimensional 
  gratings 
  for 
  .X-rays, 
  the 
  investigations 
  of 
  Barkla, 
  

   Sadler, 
  Whiddington 
  and 
  Kaye 
  brought 
  out 
  the 
  following 
  facts. 
  

   The 
  coefficient 
  of 
  absorption 
  of 
  a 
  given 
  element 
  for 
  the 
  charac- 
  

   teristic 
  X-radiations 
  emitted 
  b}^ 
  a 
  series 
  of 
  elements, 
  taken 
  in 
  the 
  

   order 
  of 
  increasing 
  atomic 
  numbers, 
  showed 
  an 
  abrupt 
  and 
  great 
  

   increase 
  when 
  the 
  incident 
  radiation 
  passed 
  through 
  the 
  wave- 
  

   length 
  corresponding 
  to 
  the 
  characteristic 
  emission 
  of 
  the 
  absorb- 
  

   ing 
  element. 
  The 
  coefficient 
  maintained 
  a 
  high 
  value 
  for 
  a 
  cer- 
  

   tain 
  interval 
  and 
  then 
  decreased, 
  as 
  the 
  frequency 
  of 
  the 
  incident 
  

   radiation 
  increased. 
  After 
  Laue's 
  discovery 
  de 
  Broglie 
  showed 
  

   (in 
  1914) 
  that 
  the 
  photographic 
  method 
  could 
  be 
  most 
  advanta- 
  

   geously 
  and 
  conveniently 
  applied 
  to 
  the 
  study 
  of 
  the 
  X-ray 
  absorp- 
  

   tion 
  bands 
  of 
  the 
  chemical 
  elements. 
  It 
  was 
  only 
  necessary 
  to 
  

   interpose 
  a 
  screen, 
  made 
  of 
  a 
  few 
  decigrams 
  of 
  the 
  absorbing 
  

   medium, 
  in 
  the 
  path 
  of 
  the 
  direct 
  rays 
  from 
  the 
  anticathode, 
  

   between 
  the 
  bulb 
  and 
  the 
  slowly 
  rotating 
  crystal 
  grating. 
  

  

  In 
  two 
  more 
  recent 
  papers 
  de 
  Broglie 
  gives 
  the 
  results 
  

   obtained 
  by 
  applying 
  this 
  method 
  to 
  the 
  JTand 
  L 
  series, 
  respec- 
  

   tively. 
  The 
  incident 
  radiations 
  were 
  produced 
  by 
  the 
  tungsten 
  

   target 
  of 
  a 
  Coolidge 
  tube, 
  and 
  a 
  crystal 
  of 
  rock-salt 
  (2d 
  = 
  5 
  # 
  63 
  

   X 
  10 
  -e 
  cm.) 
  was 
  used 
  to 
  analyze 
  the 
  rays 
  transmitted 
  by 
  the 
  

   screen. 
  For 
  the 
  K 
  series 
  seventeen 
  elements, 
  from 
  bromine 
  to 
  

   cerium, 
  having 
  smaller 
  atomic 
  numbers 
  than 
  tungsten, 
  were 
  inves- 
  

   tigated. 
  The 
  glancing 
  angles 
  for 
  the 
  edges 
  of 
  the 
  bands 
  are 
  all 
  

   tabulated, 
  the 
  values 
  for 
  the 
  extreme 
  elements, 
  bromine 
  and 
  

   cerium, 
  are 
  given 
  as 
  9° 
  20*5' 
  and 
  3° 
  2', 
  respectively. 
  Six 
  elements 
  

   having 
  greater 
  atomic 
  numbers 
  than 
  tungsten 
  (platinum 
  to 
  bis- 
  

   muth) 
  gave 
  angles 
  decreasing 
  from 
  1° 
  31*5' 
  to 
  1° 
  20'. 
  The 
  corre- 
  

   sponding 
  wave-length 
  for 
  bismuth 
  was 
  calculated 
  to 
  be 
  1*3 
  X 
  

   10~ 
  9 
  cm. 
  

  

  In 
  the 
  case 
  of 
  the 
  L 
  series 
  one 
  angle 
  is 
  given 
  for 
  each 
  of 
  the 
  

   elements 
  platinum 
  and 
  thorium, 
  while 
  two 
  angles 
  are 
  recorded 
  for 
  

   gold, 
  lead, 
  and 
  uranium. 
  The 
  glancing 
  angles 
  for 
  "band 
  I" 
  

   were 
  found 
  to 
  be 
  10° 
  55-5' 
  and 
  7° 
  20' 
  for 
  platinum 
  and 
  uranium, 
  

   in 
  the 
  order 
  named. 
  It 
  is 
  stated 
  that 
  each 
  of 
  these 
  five 
  elements 
  

   has 
  a 
  third 
  absorption 
  band 
  which 
  is 
  weaker 
  and 
  of 
  slightly 
  

   inferior 
  wave-length 
  to 
  "band 
  II." 
  It 
  thus 
  appears 
  that 
  the 
  L 
  

   series 
  involves 
  a 
  group 
  of, 
  at 
  least, 
  three 
  bands. 
  For 
  the 
  edges 
  

   of 
  homologous 
  bands 
  both 
  in 
  the 
  JTand 
  in 
  the 
  L 
  series 
  Moseley's 
  

   linear 
  law 
  was 
  found 
  to 
  represent 
  the 
  experimental 
  data 
  satisfac- 
  

   factorily. 
  — 
  Comptes 
  rendus, 
  clxii, 
  pp. 
  87, 
  352, 
  July 
  and 
  October, 
  

   1916. 
  h. 
  s. 
  u. 
  

  

  6. 
  Finite 
  Collineation 
  Groups 
  ; 
  by 
  H. 
  F. 
  Blichfeldt. 
  Pp. 
  

   xi, 
  194. 
  Chicago, 
  1917 
  (The 
  Univ. 
  of 
  Chicago 
  Press).— 
  The 
  

   theory 
  of 
  finite 
  collineation 
  groups 
  (or 
  linear 
  groups) 
  as 
  developed 
  

   so 
  far 
  is 
  to 
  be 
  found 
  mainly 
  in 
  scattered 
  articles 
  in 
  mathematical 
  

   journals 
  and 
  in 
  a 
  few 
  texts 
  on 
  group 
  theory. 
  In 
  the 
  present 
  vol- 
  

   ume 
  the 
  author 
  has 
  endeavored 
  to 
  give 
  an 
  outline 
  of 
  the 
  different 
  

  

  Am. 
  Jour. 
  Sci. 
  —Fourth 
  Series, 
  Vol. 
  XLIII, 
  No. 
  258.— 
  June, 
  1917. 
  

   33 
  

  

  