104 PHILOSOPHICAL TRANSACTIONS. [aNNO 1776. 



siderably magnified, All the crystals are not by any means formed with the 

 same exactness as those described ; some having the hexagonal form less dis- 

 tinctly marked ; bnt the regularity of most of them is so obvious, that no doubt 

 can remain of the perfection of the crystallization. 



Another kind of vitreous crystallization appears on the piece of glass marked 

 N° 2, which was taken from the bottom of a pot, that had been pulled out of 

 the furnace while the glass was red hot. The crystals are of 2 kinds ; those 

 represented by fig. 6 are of the columnar forin ; their altitude is about the 8th of 

 an inch, and the diameter of their bases about a 5th part of their altitude ; their 

 sides seem to be irregularly fluted, or cut in grooves. The other kinds of 

 crystals, represented by fig. 7 , 8, and 9, have bases of nearly the same dia- 

 meter as the columnar ones ; but their altitude is much less, being only about a 

 6th part of their diameter. Their bases are bounded by lines seemingly ragged 

 and irregular ; but several of them show a tendency to an hexagonal form, the 

 regularity of which may have been disturbed by the motion of the melted glass 

 acting on and bending these very thin crystals, while they were hot and flexible, 

 at the time when the pot was drawn out of the furnace. 



The specimens marked N° 4, are pieces of a glass-house pot, down the outer 

 sides of which some melted glass had run, and adhered long enough for the 

 formation of various kinds of crystals. The inner sides also of these pieces 

 are covered with glass variousl) crystallized. Some of these crystals seem to be 

 semi-columns, of which the flat sides, or interior surfaces, are exposed to view, 

 and are represented by fig. 10. Other crystals, represented by fig. 11, seem to 

 consist of several semi-columnar ones, uniting together in the same plane round 

 a common centre, like broad, flat spokes of a wheel. Many of these spokes 

 seem to become narrower as they approach the centre of the wheel, and there- 

 fore resemble more the segments of frusta of cones cut along their axis, than of 

 cylinders. But perhaps this appearance proceeds only from the semi-columns 

 being so disposed near the centre of the wheel, that the edge of one is laid 

 over the edge of the contiguous semi-column, like the spokes of a fan. 



In the specimen of glass, marked N" 4, which had run through a crack in a 

 pot, and had remained adhering to the bars of the grate of a furnace sufficiently 

 long for a crystallization to take place ; some of the crystals appear oblong and 

 needle-like, and others globular, or nearly of the globular form. In this piece 

 of glass, many of the needle-like crystals are seen to unite round a common 

 centre ; and though they have probably been prevented, by the too sudden 

 cooling of the glass, from concreting in a sufRcient number to jnake complete 

 globular crystals, yet they sufficiently show the manner in which those which are 

 complete have boeen formed. All the crystallizations, hitherto described, were 

 observed in a dark, green window-glass, made at Stourbridge, and called broad- 



