Page:Proceedings of the Royal Society of London Vol 1.djvu/172

Rh particles of the mass be continued, another change immediately commences, 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 secondary 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 deﬁned 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 arrangement, 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 discovered.

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 radiated 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 temperature, 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