﻿H. 
  P. 
  Whitloch 
  — 
  Crystal 
  Structure. 
  259 
  

  

  Aet. 
  XVIII. 
  — 
  A 
  Model 
  for 
  Demonstrating 
  Crystal 
  Struc- 
  

   ture; 
  by 
  Hekbert 
  P. 
  Whitlock. 
  

  

  The 
  interest, 
  both 
  scientific 
  and 
  popular, 
  in 
  atomic 
  

   groupings 
  in 
  relation 
  to 
  crystal 
  structure 
  which 
  has 
  been 
  

   created 
  by 
  the 
  recent 
  work 
  of 
  W. 
  H. 
  and 
  W. 
  L. 
  Bragg 
  

   and 
  others 
  has 
  caused 
  a 
  demand 
  for 
  some 
  means 
  of 
  pre- 
  

   senting 
  to 
  an 
  audience, 
  either 
  in 
  the 
  class 
  room 
  or 
  from 
  

   the 
  lecture 
  table, 
  the 
  essential 
  facts 
  of 
  these 
  group 
  move- 
  

   ments. 
  The 
  difficulty 
  encountered 
  in 
  representing 
  com- 
  

   plex 
  particle 
  combinations 
  in 
  any 
  series 
  of 
  diagrams 
  

   involving 
  their 
  projection 
  upon 
  a 
  flat 
  surface 
  has 
  led 
  the 
  

   writer 
  to 
  resort 
  to 
  three 
  dimensional 
  models 
  of 
  various 
  

   constructions, 
  the 
  latest 
  and 
  most 
  effective 
  of 
  which 
  is 
  the 
  

   subject 
  of 
  the 
  present 
  paper. 
  The 
  principle 
  involved, 
  

   that 
  of 
  supporting 
  a 
  series 
  of 
  inconspicuous 
  rods 
  carry- 
  

   ing 
  beads 
  spaced 
  at 
  appropriate 
  intervals 
  by 
  means 
  of 
  

   two 
  perforated 
  diaphrams, 
  is 
  not 
  new. 
  Models 
  of 
  this 
  

   general 
  type 
  were 
  described 
  by 
  Bowman 
  in 
  1910, 
  1 
  and 
  

   somewhat 
  similar 
  models 
  were 
  suggested 
  by 
  Sohncke 
  in 
  

   1879. 
  2 
  The 
  writer 
  in 
  constructing 
  the 
  present 
  model 
  has 
  

   endeavored 
  to 
  produce 
  a 
  demonstrating 
  device 
  which 
  

   may 
  be 
  readily 
  put 
  together 
  and 
  taken 
  apart 
  while 
  the 
  

   demonstrator 
  is 
  speaking, 
  which 
  is 
  plainly 
  visible 
  to 
  a 
  

   fairly 
  large 
  group 
  of 
  auditors, 
  and 
  which, 
  by 
  using 
  inter- 
  

   changeable 
  rods, 
  may 
  be 
  employed 
  to 
  demonstrate 
  and 
  

   study 
  any 
  point 
  system 
  of 
  atomic 
  spacing. 
  

  

  The 
  frame 
  work 
  of 
  the 
  model, 
  which 
  is 
  illustrated, 
  

   partly 
  cut 
  away 
  to 
  show 
  the 
  construction, 
  in 
  fig. 
  1, 
  con- 
  

   sists 
  essentially 
  of 
  a 
  wooden 
  block 
  9 
  inches 
  square 
  sur- 
  

   mounted 
  by 
  two 
  narrow 
  frames, 
  each 
  % 
  inch 
  deep, 
  and 
  

   finished 
  with 
  a 
  narrow 
  moulding. 
  Between 
  the 
  two 
  

   frames 
  and 
  between 
  the 
  top. 
  frame 
  and 
  the 
  moulding 
  are 
  

   inserted 
  two 
  sheets 
  of 
  tin, 
  which 
  previous 
  to 
  their 
  assem- 
  

   bling 
  have 
  been 
  clamped 
  together 
  and 
  punched 
  with 
  holes 
  

   laid 
  out 
  by 
  means 
  of 
  a 
  carefully 
  constructed 
  pattern. 
  

   The 
  holes 
  should 
  be 
  of 
  such 
  a 
  diameter 
  that 
  they 
  will 
  

   readily 
  take 
  a 
  glass 
  rod 
  of 
  3 
  mm. 
  diameter, 
  and 
  in 
  clamp- 
  

   ing 
  the 
  sheets 
  of 
  tin 
  together 
  with 
  the 
  pattern 
  the 
  

   punched 
  holes 
  are 
  made 
  to 
  register 
  accurately. 
  

  

  Two 
  such 
  frameworks 
  or 
  stands 
  are 
  necessary, 
  one 
  

  

  1 
  H. 
  L. 
  Bowman, 
  Min. 
  Mag., 
  16, 
  51, 
  1910. 
  

  

  2 
  L. 
  Sohncke, 
  Entwiekelung 
  einer 
  Theorie 
  der 
  Krystallstructur, 
  Leipzig, 
  

   1879. 
  

  

  Am. 
  Jour. 
  Sci.— 
  Fourth 
  Series, 
  Vol. 
  XL1X, 
  No. 
  292.— 
  April, 
  1920. 
  

   19 
  

  

  