SIR DAVID BREWSTER ON CIRCULAR CRYSTALS. 619 
Negative Circular Crystals. 
Borax in phosphoric acid. Sulphate of copper and iron, 
Lithoxanthate of ammonia. he bie zine. 
Salicine. magnesia. 
Asparagine. magnesia of potash. 
Manna. copper of ammonia. 
Parmeline. zine of ammonia, 
Palmic acid. a5! zine. 
Palmine. Substance in garnet. 
Esculine. Stearine.* 
Berberine. Stearic acid. 
Cinchonine. Palmitic acid. 
Theine. Acetate of strontian. 
Oil of mace. f quinine. 
Cacao butter. Chloride of zinc. 
Hatchetine. Oxide of uranium. 
Animal fat. Protoxide of nickel. 
White wax. Phosphate of nickel. 
Chrysoleplinic acid. 
Succinate of zinc. 
Chromic acid. 
Citric acid. 
Nitrate of uranium. 
urea. 
brucine. 
strychnine. 
Gallic acid. 
Thianuret of ammonia. 
Sulphuret of cadmium. 
Carbonate of nickel. 
Substance in mica. 
Adipocire. 
Margarie 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. Hoof of rhinoceros. 
ass, transverse section. Horn of rhinoceros, transverse and vertical. 
Transparent aperture in the wing of the ... antelope. 
beetle. Hairs of animals, sections of. 
In examining the crystallisations of the Chromate and Protochloride 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. 8E 
