OP ARTS AND SCIENCES. 481 



inclined to each other at the regular octahedral angle (109° 28') 

 as nearly as the uneven surfaces of the faces would admit of measure- 

 ment with an application goniometer. This large, unique, isolated 

 octahedron, of massive iron, measures seven inches in its longest 

 dimension, and one of the triangular faces distinctly outlined measures 

 over four inches on each edge. Another face, still more distinctly 

 marked, measures three inches on each edge. At various points there 

 are triangular depressions or reliefs conforming to the general outline, 

 features which are so characteristic of large crystals ; and there are 

 also numerous rifts parallel to the octahedral faces. A large part of 

 the surface is covered with a crust, and, on the basis of the usual 

 interpretation of meteoric phenomena, it is obvious that this crystal 

 is the fragment of an iron meteorite broken up after entering the 

 atmosphere, but while still moving rapidly enough to produce a melted 

 crust over the surface of fracture. 



Another example in the Harvard collection of external octahedral 

 form is a specimen of the Carthage (Smith Co.) iron. This speci- 

 men shows six faces of a rough octahedron, one of the faces having an 

 area of seven square inches. One half of this octahedron has been 

 partially torn apart into numerous smaller crystals, some of them an 

 inch or more in diameter ; but though the crevasses between the 

 individuals are in some places nearly a quarter of an inch in breadth, 

 yet they are bound firmly together by a network of plates, which in 

 some parts raggedly jut out from the octahedral faces. The general 

 appearance of the exterior of the specimen reminds one somewhat of 

 a rough mass of galena crystals, only of octahedral form. The rough 

 crystal is evidently the result of fracture, probably caused during the 

 passage of the mass through the air, and the octahedral faces are 

 cleavage planes, if the term cleavage may be applied to such fractures, 

 which cannot be reproduced by splitting in the ordinary way on 

 account of tiie malleability of the mass. The specimen further ex- 

 hibits a fused crust over the octahedral faces, which must have formed 

 after the partial breaking up of the large mass, giving a rounded 

 appearance to the edges. On a polished surface, cut nearly parallel 

 to the largest octahedral face, the figures produced by etching apjDcar 

 very strikingly. They are perfectly distinct and regular, being typical 

 Widmanstattian figm-es ; but when they come to the cracked portion 

 of the iron, they appear as separate plates, some having been broken 

 by the rupture, others separated, while the greater number appear 

 bent and strained, but still coherent and binding the mass firmly to- 

 gether. The whole appearance on the etched surface gives at once 



VOL. XIII. (n. S. XXI.) 31 



