152 



particles of the mass be continued, another change immediately com- 

 mences, in the progress of which the whole acquires a more stony 

 texture, and a greater degree of tenacity. This is generally effected 

 by a gradual formation of secondaiy spheroids in the heart of the 

 jaspideous substance, whose centres are more distant, and dimensions 

 greater than those of the above-mentioned globules : they are radiated 

 with distinct fibres. When two of these spheroids come into contact 

 by mutual enlargement, no intermixture of their fibres seems to take 

 place ; they reciprocally compress each other, and their limits are de- 

 nned by planes, at which a distinct separation takes place. When 

 several spheroids come in contact on the same level, they are formed 

 by mutual pressure into prisms of tolerable regularity, whose division 

 is perfectly defined : and when a spheroid is surrounded on all sides 

 by others, it is compressed into an irregular polyhedron. 



The transition from this fibrous state to a different arrangement, 

 seems to be very rapid, for the centres of most of the spheroids be- 

 come quite compact before they receive one quarter of their usual 

 dimensions ; the mass then becomes perfectly solid, very tenacious, 

 and opake ; and its hardness is somewhat inferior to that of the glass 

 from which it is formed. 



A further continuation of the temperature, favourable to arrange- 

 ment, speedily occasions another change. The texture of the mass 

 becomes more granular, and the brilliant points it exhibited in its 

 former state become larger and more numerous, arrange themselves 

 into regular forms, and finally, the whole mass becomes pervaded by 

 thin crystalline laminae, which intersect it in every direction, and 

 form projecting crystals in the cavities. 



It is thought that an equalized temperature would have rendered 

 the whole mass at once similar to the substance last described ; but 

 then the interesting initial phenomena, from which the important 

 inferences here announced are deduced, would not have been dis- 

 covered. 



These, and many more facts relating to the experiment, having 

 been minutely detailed, the author proceeds to offer what he deems 

 a partial explanation of the formation of the globules and of the ra- 

 diated spheroids. It is well ascertained, he says, that heat is emitted 

 by all bodies in their change from a gaseous to a fluid state ; and it 

 is reasonable to suppose that heat may also be emitted in those 

 changes of arrangement which affect the internal texture of a body 

 after it has attained an apparently solid state. 



That a succession of such changes actually takes place, seems to 

 be demonstrated by several of the appearances in the experiment, 

 and particularly by the increase of specific gravity, which generally 

 keeps pace with the internal changes of the substance. These changes, 

 it is conjectured, may be caused by a gradual diminution of tempe- 

 rature, which permits certain laws to induce peculiar arrangements 

 among the particles of the glass : when several of these particles 

 enter into this new bond of association, they must form a minute 

 point, from which heat will issue in every direction : that heat will 



