﻿Chemistry 
  and 
  Physics. 
  421 
  

  

  perpendicular 
  to 
  the 
  face 
  of 
  the 
  mica 
  sheet 
  and 
  containing 
  the 
  

   axis 
  of 
  the 
  primary 
  pencil. 
  The 
  number 
  and 
  orientation 
  of 
  these 
  

   interference 
  patterns 
  are 
  different 
  on 
  the 
  various 
  negatives, 
  due 
  

   to 
  intentional 
  changes 
  in 
  the 
  sizes 
  and 
  relative 
  positions 
  of 
  the 
  

   mica, 
  collimating 
  holes, 
  etc. 
  Thus 
  the 
  possibility 
  of 
  interference 
  

   of 
  y-rays 
  scattered 
  or 
  reflected 
  at 
  the 
  cleavage 
  planes 
  of 
  mica 
  has 
  

   been 
  demonstrated 
  experimentally. 
  Three 
  exposures 
  were 
  made 
  

   with 
  a 
  glancing 
  angle 
  of 
  about 
  five 
  degrees 
  but 
  no 
  grating 
  effects 
  

   were 
  recorded. 
  The 
  y-ray 
  negatives 
  were 
  compared 
  both 
  with 
  a 
  

   negative 
  obtained 
  with 
  X-rays 
  under 
  similar 
  conditions, 
  taken 
  by 
  

   the 
  investigator 
  himself, 
  and 
  with 
  X-ray 
  photographs 
  taken 
  by 
  

   Bragg. 
  Shaw 
  says 
  : 
  " 
  Since 
  it 
  is 
  thus 
  apparent 
  that 
  we 
  get 
  

   faint 
  effects 
  with 
  y-rays 
  in 
  those 
  directions 
  in 
  which 
  very 
  hard 
  

   X-rays 
  give 
  their 
  most 
  intense 
  reflections, 
  and 
  no 
  perceptible 
  

   effect 
  in 
  the 
  direction 
  in 
  which 
  soft 
  X-rays 
  give 
  their 
  strongest 
  

   reflection, 
  we 
  may 
  conclude 
  that 
  the 
  wave-length 
  of 
  the 
  soft 
  

   y-rays 
  from 
  radium 
  is 
  less 
  than 
  that 
  of 
  hard 
  X-rays 
  by 
  an 
  amount 
  

   not 
  differing 
  greatly 
  from 
  the 
  difference 
  in 
  wave-length 
  between 
  

   the 
  softest 
  and 
  the 
  hardest 
  X-rays 
  that 
  can 
  be 
  produced 
  with 
  an 
  

   ordinary 
  bulb 
  and 
  coil." 
  Assuming 
  that 
  the 
  known 
  relation 
  

   between 
  the 
  velocity 
  of 
  electrons 
  from 
  surfaces 
  and 
  the 
  fre- 
  

   quency 
  of 
  the 
  ultra-violet 
  light 
  which 
  liberates 
  them 
  can 
  be 
  

   extended 
  to 
  y 
  rays 
  and 
  to 
  X-rays, 
  and 
  using 
  Planck's 
  formula 
  

   £mv* 
  = 
  hn, 
  it 
  follows 
  that 
  ordinary 
  y-rays 
  from 
  radium 
  have 
  

   wave-lengths 
  probably 
  about 
  ten, 
  or 
  at 
  most 
  a 
  hundred, 
  times 
  

   smaller 
  than 
  the 
  wave-length 
  of 
  the 
  hardest 
  Rontgen 
  rays. 
  — 
  Phil. 
  

   Mag., 
  vol. 
  xxvi, 
  July, 
  1913, 
  p. 
  190. 
  h. 
  s. 
  tj. 
  

  

  8. 
  Experimental 
  Researches 
  on 
  the 
  Specific 
  Gravity 
  and 
  Dis- 
  

   placement 
  of 
  Some 
  Saline 
  Solutions 
  ; 
  by 
  J. 
  Y. 
  Buchanan. 
  Pp. 
  

   227. 
  Edinburgh, 
  1912 
  (Neilland 
  Co.). 
  — 
  This 
  memoir 
  is 
  reprinted 
  

   from 
  the 
  Transactions 
  of 
  the 
  Royal 
  Society 
  of 
  Edinburgh, 
  Vol. 
  

   XLIJl, 
  Part 
  I, 
  1912. 
  — 
  " 
  The 
  main 
  purpose 
  of 
  the 
  investigation 
  

   was 
  to 
  determine 
  the 
  specific 
  gravity 
  of 
  solutions 
  of 
  moderate 
  

   concentration 
  and 
  of 
  high 
  dilution." 
  The 
  data 
  were 
  obtained 
  by 
  

   using 
  specially 
  designed 
  hydrometers, 
  and 
  hence 
  a 
  great 
  deal 
  of 
  

   space 
  is 
  devoted 
  to 
  an 
  account 
  of 
  the 
  construction 
  and 
  manipula- 
  

   tion 
  of 
  these 
  hydrometers, 
  and 
  also 
  to 
  the 
  high 
  degree 
  of 
  accu- 
  

   racy 
  attainable. 
  The 
  salts 
  studied 
  with 
  the 
  closed 
  hydrometer 
  

   were 
  the 
  bromides, 
  chlorides, 
  iodides, 
  bromates, 
  chlorates, 
  iodates, 
  

   and 
  nitrates 
  of 
  potassium, 
  rubidium 
  and 
  caesium, 
  and 
  also 
  the 
  

   nitrates 
  of 
  lithium, 
  sodium, 
  strontium, 
  barium 
  and 
  lead. 
  The 
  

   chlorides 
  of 
  beryllium, 
  magnesium 
  and 
  calcium 
  were 
  investigated 
  

   with 
  the 
  open 
  hydrometer. 
  The 
  tables 
  are 
  numerous 
  and 
  repre- 
  

   sent 
  an 
  enormous 
  amount 
  of 
  work 
  which 
  was 
  apparently 
  done 
  in 
  

   the 
  most 
  painstaking 
  manner 
  possible. 
  The 
  results 
  obtained 
  

   from 
  the 
  discussion 
  of 
  the 
  numerical 
  data 
  are 
  new 
  and 
  important, 
  

   but 
  far 
  too 
  numerous 
  to 
  admit 
  of 
  recapitulation 
  in 
  this 
  place. 
  

   One 
  typical 
  illustration 
  must 
  suffice. 
  

  

  "The 
  most 
  noteworthy 
  case 
  is 
  that 
  of 
  calcium 
  chloride 
  in 
  

   supersaturated 
  solution. 
  In 
  it 
  a 
  very 
  remarkable 
  state 
  of 
  unrest 
  

  

  