108 PHILOSOPHICAL TRANSACTIONS. [aNNO 1770. 



texture as the columns themselves, seems to be a mass irregularly crystallized, 

 analogous to the irregularly-shaped masses in the specimens of glass N" 1 and 

 2, which evidently consist of a similar substance as the neighbouring crystals, 

 and seem to have been composed of a number of these crystals indistinctly 

 united ; for the peculiar figures of crystals are distinct only when they are 

 insulated, or when they are separated from each other by a pellucid or differently- 

 coloured medium. A medium of this kind appears between the vitreous 

 crystals, and is nothing else but the more fluid parts of the glass, which longer 

 resist the concretion, but which, by a further continuance of the heat would 

 have become with the parts already crystallized, one uniform, white, opaque 

 substance, without any interposition of transparent glass, or distinction of 

 crystal, except on the surface, as in specimen N" 5, in which the crystals stand 

 prominent from the indistinct mass, and unenveloped in any medium, in the 

 same manner as the basaltic crystallizations appear standing above the mass of 

 stone or lava which supports them. 



Further observations on the basaltic and vitreous crystals may probably suggest 

 more instances of analogy between these two substances. No just objection can be 

 drawn against this analogy from the magnitude ot the former compared with 

 the minuteness of the latter : for the difference of size between the small 

 vitreous crystals and the stupendous basaltic columns, which support mountains, 

 islands, and provinces, is no more than is proportionate to the difference usually 

 observed between the little works of art and the magnificent operations of 

 nature. 



XXX f^. A Belt on the Disc of Saturn described in an Extract of a Letter from 

 Mr. Messier, F. R. S., to Mr. Magellan, F. R. S. Dated Paiis, May 29, 

 1776. p. 543. 



I have observed, since the 14th of May, a belt of a 'ainter light on the body 

 of Saturn, opposite to the part of the ring behind the planet. It is pretty 

 broad, and almost as distinct as those of Jupiter. It was with a very good 

 achromatic of 3 feet and a half", made by Dollond, that I discovered this 

 appearance. I wish you would communicate it to the astronomers, because 

 those who are furnished with better instruments may perhaps see some 

 inequalities in this belt of Saturn, and so the time of the planet's revolution on 

 its axis may be better ascertained than it is at present. Messrs. John and James 

 Cassini seem to have been the only astronomers who discovered this phenomenon 

 about the end of the last century. 



XXXVl. All Account of some Poisonous Fish in the South Seas.* By Mr. 

 fFm. Aiulerson, Surgeon of H. M. Ship the Resolution, p. 544. 



• The fishes which caused the symptoms detailed in this paper appear to have been die Tetrodoii 



