VOL. LXVI.] PHILOSOPHICAL TRANSACTIONS. 103 



in their transition from a fluid to a solid state, would, if this transition were not 

 effected too hastily, concrete into crystals, or bodies similarly figured. Instances 

 of such crystallization have occurred in glass, which had passed very slowly 

 from a fluid to a solid state ; and the form, regularity, and size of these 

 vitreous crystals have varied according to the circumstances with which their 

 concretions had been accompanied. Mr. K. sent, along with this paper, a few 

 specimens of this crystallized glass, together with a drawing of some of the 

 most remarkable crystals. 



The pieces of glass, marked N° 1 , were taken from the bottom of a large 

 pot, which had stood in a glass-house furnace at the time the fire was allowed 

 gradually to extinguish. In this case, the mass of heated matter was so great, 

 that without the addition of fuel, the heat continued long, and the transition 

 of the glass from a fluid to a solid state was very slowly accomplished. The 

 upper part of this glass was found to be changed into a white, semi-opaque 

 substance, resembling in colour and texture some of the white spars. Under 

 this crust, which, in some places, was a quarter of an inch thick, and in others 

 more, the glass was transparent, but considerably obscured, and its colour was 

 changed from a dark green to a dull blue. In this semi-pellucid glass were 

 dispersed many white, opaque, regular crystals, the form of which was generally 

 that of a solid, whose side view is represented by fig. 1, and its basis by fig. 3, 

 pi. 1. The surface of these crystals seems to be bounded by lines rather ellip- 

 tical than circular, which are so disposed, that a transverse section of a crystal, 

 that is, a section perpendicular to its axis, is a hexagon, as in fig. 4 and 5 ; the 

 former of which represents a view, and the latter a plan, of that section. In 

 the middle of each basis of the crystal, a conical cavity appears, as in fig. 2 and 

 3. The elliptical lines which bound the surface of the crystals seem to be occa- 

 sioned by the edges of many thin plates, so arranged round the axis of each 

 crystal, that their longitudinal diameters are parallel to that axis. Of these 

 plates, 12 are larger, more conspicuous, and better defined, than the rest. 

 They are placed in pairs, at an equal distance from each other, forming the Q 

 angles of the hexagonal section and basis, as appears in fig. 2, 3, 4 and 5. The 

 intervals between the pairs of plates, that is, the areas of the triangles into 

 which the hexagonal section is divided by these pairs, are filled up partly by 

 smaller plates aflixed to the sides of the principal plates, and of each other, at 

 an angle of 60°, and partly by a substance somewhat less opaque and darker 

 coloured than that of the plates. The size of the contiguous and of the neigh- 

 bouring crystals does not vary much, though that of crystals found at different 

 depths of the same pot were observed to differ considerably. The greatest 

 diameter of the crystals from which the figures 2, 3, 4, and 5, were copied, 

 was about -sV part of an inch, so that these figures represent the crystals con- 



