﻿SIR 
  DAVID 
  BREWSTER 
  ON 
  CIRCULAR 
  CRYSTALS. 
  

  

  619 
  

  

  Borax 
  in 
  phosphoric 
  acid. 
  

  

  Lithoxanthate 
  of 
  ammonia. 
  

  

  Salicine. 
  

  

  Asparagine. 
  

  

  Manna. 
  

  

  Parmeline. 
  

  

  Palmic 
  acid". 
  

  

  Palmine. 
  

  

  Esculine. 
  

  

  Berberine. 
  

  

  Cinchonine. 
  

  

  Theine. 
  

  

  Oil 
  of 
  mace. 
  

  

  Cacao 
  butter. 
  

  

  Hatchetine. 
  

  

  Animal 
  fat. 
  

  

  White 
  wax. 
  

  

  Chrysoleplinic 
  acid. 
  

  

  Succinate 
  of 
  zinc. 
  

  

  Chromic 
  acid. 
  

  

  Citric 
  acid. 
  

  

  Nitrate 
  of 
  uranium. 
  

  

  urea. 
  

  

  brucine. 
  

  

  strychnine. 
  

   Gallic 
  acid. 
  

  

  Thianuret 
  of 
  ammonia. 
  

   Sulphuret 
  of 
  cadmium. 
  

  

  Negative 
  Circular 
  Crystals. 
  

  

  Sulphate 
  of 
  copper 
  and 
  iron. 
  

  

  zinc. 
  

  

  magnesia, 
  

   magnesia 
  of 
  potash, 
  

   copper 
  of 
  ammonia, 
  

   zinc 
  of 
  ammonia. 
  

  

  zinc. 
  

   Substance 
  in 
  garnet. 
  

   Stearine.* 
  

   Stearic 
  acid. 
  

   Palmitic 
  acid. 
  

   Acetate 
  of 
  strontian. 
  

  

  quinine. 
  

   Chloride 
  of 
  zinc. 
  

   Oxide 
  of 
  uranium. 
  

   Protoxide 
  of 
  nickel. 
  

   Phosphate 
  of 
  nickel. 
  

   Carbonate 
  of 
  nickel. 
  

   Substance 
  in 
  mica. 
  

   Adipocire. 
  

   Margaric 
  acid. 
  

   Ethal. 
  

  

  Oxalurate 
  of 
  ammonia. 
  

   Kreatine. 
  

  

  Carbazotate 
  of 
  potash. 
  

   Sulphuret 
  of 
  potassium. 
  

   Hippuric 
  acid. 
  

   Santonine. 
  

  

  To 
  this 
  list 
  of 
  substances 
  which, 
  under 
  certain 
  favourable 
  conditions 
  of 
  crystal- 
  

   lisation, 
  after 
  solution 
  or 
  fusion, 
  give 
  circular 
  crystals, 
  the 
  perfection 
  of 
  which 
  

   depends 
  on 
  causes 
  over 
  which 
  the 
  observer 
  has 
  little 
  control, 
  I 
  may 
  add 
  the 
  fol- 
  

   lowing 
  animal 
  substances, 
  in 
  which 
  the 
  circular 
  phenomena 
  are 
  produced, 
  and 
  

   in 
  which, 
  with 
  one 
  exception, 
  the 
  structure 
  is 
  negative, 
  as 
  the 
  greater 
  number 
  of 
  

   such 
  structures 
  seem 
  to 
  be. 
  

  

  Hoof 
  of 
  horse, 
  both 
  transverse 
  and 
  vertical. 
  

  

  ass, 
  transverse 
  section. 
  

   Transparent 
  aperture 
  in 
  the 
  wing 
  of 
  the 
  

   beetle. 
  

  

  Hoof 
  of 
  rhinoceros. 
  

  

  Horn 
  of 
  rhinoceros, 
  transverse 
  and 
  vertical. 
  

  

  . 
  . 
  . 
  antelope. 
  

   Hairs 
  of 
  animals, 
  sections 
  of. 
  

  

  In 
  examining 
  the 
  crystallisations 
  of 
  the 
  Chromate 
  and 
  Protochloricle 
  of 
  Mercury, 
  

   and 
  of 
  the 
  Sulphuret 
  of 
  Bismuth, 
  I 
  found 
  that 
  they 
  exhibited 
  the 
  hemispherical 
  

  

  * 
  Stearine 
  gives 
  the 
  same 
  polarised 
  halos 
  as 
  oil 
  of 
  mace. 
  

  

  VOL. 
  XX. 
  PART 
  IV. 
  

  

  8 
  E 
  

  

  