﻿260 
  

  

  H. 
  P. 
  Whitloch—A 
  Model 
  for 
  

  

  laid 
  out 
  in 
  centered 
  squares 
  spaced 
  to 
  about 
  25 
  mm., 
  or 
  

   one 
  inch, 
  for 
  groupings 
  in 
  the 
  isometric 
  and 
  tetragonal 
  

   systems 
  ; 
  this 
  may 
  also 
  be 
  used 
  for 
  orthorhombic, 
  mono- 
  

   clinic 
  and 
  triclinic 
  groupings. 
  The 
  second 
  stand 
  is 
  laid 
  

   out 
  in 
  equilateral 
  triangles 
  of 
  similar 
  spacing, 
  for 
  hex- 
  

   agonal 
  and 
  rhomb 
  ohedral 
  groupings, 
  and 
  may 
  also 
  be 
  

   used 
  for 
  orthorhombic, 
  monoclinic 
  and 
  triclinic 
  lattices. 
  

   The 
  atoms 
  are 
  represented 
  by 
  spherical 
  wooden 
  beads, 
  

   one 
  half 
  inch 
  in 
  diameter, 
  which 
  may 
  be 
  obtained 
  in 
  six 
  

   colors 
  from 
  dealers 
  in 
  kindergarten 
  supplies. 
  3 
  The 
  sup- 
  

   porting 
  rods 
  are 
  cut 
  from 
  ordinary 
  glass 
  rod 
  stock 
  of 
  a 
  

   diameter 
  which 
  will 
  fit 
  the 
  holes 
  in 
  the 
  wooden 
  beads. 
  

  

  The 
  rods 
  are 
  cut 
  accurately 
  to 
  the 
  desired 
  length 
  and 
  

   the 
  beads 
  are 
  spaced 
  accurately 
  on 
  them 
  and 
  fastened 
  

   with 
  a 
  drop 
  of 
  glue. 
  It 
  was 
  found 
  convenient 
  to 
  adopt 
  

   for 
  isometric 
  groupings 
  a 
  cube 
  of 
  10 
  cm. 
  (4 
  inches), 
  

   which 
  takes 
  four 
  spacings 
  between 
  holes 
  of 
  the 
  frame 
  and 
  

   permits 
  the 
  construction 
  of 
  all 
  the 
  simple 
  isometric 
  crys- 
  

   tal 
  structures. 
  

  

  A 
  few 
  illustrations 
  will 
  serve 
  to 
  show 
  the 
  method 
  of 
  

   using 
  the 
  model, 
  which 
  has 
  been 
  tried 
  out 
  before 
  several 
  

   audiences. 
  Fig. 
  2 
  shows 
  the 
  model 
  arranged 
  to 
  illus- 
  

   trate 
  the 
  space 
  lattice 
  of 
  a 
  centered 
  cube. 
  The 
  dodeca- 
  

   hedral 
  planes 
  of 
  particle 
  crowding 
  are 
  "here 
  accentuated. 
  

   Removing 
  the 
  outer 
  rods 
  and 
  substituting 
  one 
  of 
  them 
  

  

  8 
  The 
  beads 
  used 
  in 
  the 
  model 
  illustrated 
  were 
  obtained 
  from 
  Milton 
  

   Bradley 
  Co. 
  

  

  