﻿SIR 
  DAVID 
  BREWSTER 
  ON 
  CIRCULAR 
  CRYSTALS. 
  023 
  

  

  goes 
  on 
  more 
  slowly, 
  and 
  in 
  a 
  more 
  singular 
  manner. 
  It 
  commences 
  at 
  the 
  hexa- 
  

   gonal 
  junctions 
  of 
  the 
  discs, 
  all 
  of 
  which 
  become 
  black 
  by 
  transmitted, 
  but 
  white 
  

   by 
  reflected 
  light. 
  These 
  minute 
  crystals, 
  which 
  are 
  transparent 
  when 
  separate, 
  

   diffuse 
  themselves 
  around, 
  as 
  if 
  they 
  had 
  fallen 
  in 
  a 
  shower. 
  The 
  same 
  kind 
  of 
  

   decomposition 
  goes 
  on 
  in 
  radial 
  lines, 
  and 
  a 
  granular 
  decomposition 
  takes 
  place 
  

   over 
  the 
  coloured 
  sectors, 
  commencing 
  at 
  their 
  centre, 
  obliterating 
  the 
  black 
  cross, 
  

   and 
  destroying 
  the 
  tints 
  of 
  all 
  orders. 
  

  

  In 
  Oil 
  of 
  Mace, 
  the 
  decomposition 
  is 
  effected 
  in 
  a 
  single 
  night. 
  The 
  area 
  of 
  

   the 
  disc 
  is 
  filled 
  with 
  drops 
  of 
  fluid 
  and 
  atoms 
  of 
  solid 
  matter 
  which 
  have 
  no 
  

   action 
  upon 
  light, 
  while 
  an 
  opaque 
  ingredient 
  occupies 
  its 
  circular 
  margin. 
  

  

  In 
  Palmerine 
  and 
  some 
  other 
  crystals, 
  the 
  film 
  decays 
  in 
  spots, 
  where 
  the 
  tint 
  

   descends 
  from 
  that 
  of 
  the 
  film 
  to 
  zero 
  in 
  concentric 
  circles, 
  while 
  in 
  other 
  spots 
  

   the 
  tint 
  rises 
  in 
  similar 
  rings, 
  as 
  if 
  the 
  atoms, 
  liberated 
  from 
  one 
  spot, 
  had 
  been 
  

   deposited 
  in 
  another. 
  

  

  Such 
  are 
  the 
  details 
  respecting 
  the 
  nature, 
  formation, 
  and 
  decomposition 
  of 
  

   circular 
  crystals, 
  which 
  I 
  wish 
  to 
  submit 
  to 
  the 
  Society. 
  Lengthened 
  as 
  they 
  are, 
  

   they 
  are 
  but 
  a 
  brief 
  abstract 
  of 
  the 
  numerous 
  observations, 
  which, 
  during 
  the 
  

   last 
  ten 
  years, 
  I 
  have 
  made 
  on 
  this 
  class 
  of 
  bodies. 
  Their 
  bearing 
  upon 
  unsettled 
  

   questions 
  in 
  the 
  molecular 
  philosophy 
  cannot 
  be 
  doubted. 
  If 
  it 
  is 
  in 
  the 
  agency 
  

   of 
  its 
  ordinary 
  laws 
  that 
  we 
  recognise 
  the 
  beauty 
  and 
  harmony 
  of 
  the 
  material 
  

   universe, 
  it 
  is 
  in 
  the 
  abnormal 
  phenomena 
  which 
  so 
  often 
  perplex 
  us, 
  that 
  Nature 
  

   discloses 
  her 
  mysteries 
  and 
  reveals 
  her 
  laws. 
  

  

  St 
  Leonard's 
  College, 
  St 
  Andrews, 
  

   \5th 
  March 
  1853. 
  

  

  VOL. 
  XX. 
  TART 
  IV. 
  8 
  F 
  

  

  