
SIR DAVID BREWSTER ON CIRCULAR CRYSTALS. 623 
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. 
Sr LEONARD’s CoLLEGE, St ANDREWS, 
15th March 1853. 
VOL. XX. PART Iv. 8r 
