848 Professor Haussmann on Melalhtrgic Crystallography. 
lion ; hut, at the same time, it appears, that the power of 
centra] attraction alone, independent of the property of crys- 
tallization, is capable of producing a regular hexagonal pris- 
matic form. By the power of attraction, the particles of the 
scorise, in the act of cooling, are drawn into certain centres ; 
hut likewise the particles of the contiguous individual spheres 
of attraction mutually attract each other. In the great- 
est approximation of the equal individual spheres of attrac- 
tion, a change takes place, by the attracting forces acting 
in opposite directions, of the circular outlines into regular 
hexagons, which possess less regularity in proportion, as 
there is a less equal approximation of the spheres of attrac- 
tion. This phenomenon appears in like mariner in the melting 
of hard bodies as in the drying of moist bodies, in the process 
of cooling lava as in the drying of potter’s clay. From the 
fibrous texture of scoria, it is evident that the property of crys- 
tallisation is conjoined with the power of central attraction. 
But this latter power does not act freely, being restrained by 
the former. In many of the planes of the spheres of attrac- 
tion, we observe fibres going off from the centre to the peri- 
pheria, in the same manner as they have been observed by Keir 
upon glass, and represented by him in Figures 6, 7, 8. of the 
Plate already quoted. 
It very seldom happens, except in the texture, that the ten- 
dency to crystallization is doubtful ; perfect crystalline forma- 
tions are observed in scoriae, of which I shall give some account 
in the following paragraphs. 
Grignonus was the first who described and represented the vi- 
treous octahedral scoria of iron, a specimen of w r hich he had re- 
ceived from a melting furnace. Torbern Bergman, in his Opuscu- 
la, and also in his Physical Geography, has noticed an octahedral 
crystalline scoria, which was obtained from a mixture of lime- 
stone with crude iron reduced into flexible iron. This specimen 
of scoria seemed to correspond with that which is sold by mine- 
ral merchants under the name of Volcanic Iron-Glass, and with 
that also, which, under a mistaken denomination, has been de- 
scribed by Karsteo, and has been subjected to a chemical pro- 
cess bv Klaproth. Their mistake was first detected by my col- 
league Stromeyer. I have given a more copious account of 
