Society of 'Natural B'iflory & Paris. *tj 



12 degrees. He has fine* found that they have for their pri- 

 mitive form a rhomboid fomewhat acute, in which the angle 

 of the fummit is about 87 degrees. 



Buthe thoughtalfo,with all othernaturaiifts, that the cryftals 

 of the iron of the ifland of Elba were derived from the cubie 

 form ; and he had referred to that form that of the cryftals of 

 Framout in dodecacdra compofed of two right pyramids in- 

 complete. He had alwavs been ftruck, however, with a kind 

 of Angularity prefented here by the cubic form which per- 

 formed the function of the rhomboid ; that is to fay, that it. 

 was ncceffary to fuppofe an axis paffing through the two op- 

 posite folid angles, which were to be confidered as the fum- 

 mits, and the laws of the decrement which took place around 

 the fummits were different from thole which related to the 

 lateral angles. 



He was (till more furprifed, when, having lately tried to 

 apply theory to a variety of the iron of Framont, which he 

 had not before examined, he obferved that it was neceffary 

 to fuppofe it to refult from a decrement by twenty rows on 

 the inferior augles of the primitive cube, in order to have re- 

 fill ts correfponding with nhiervation. 



This law, though perfectly admiffible, deviated fo much 

 from the ufual laws, that it infpircd the author with fufpicions 

 refpeding the cubic form itfelf, and, by the help of goniome- 

 try, he meafjred, for the fir ft time, on the cryftals of the 

 ifland of Elba, the mutual incidence of the primitive face's; 

 whereas he had before confined himfelf to meafuring that 

 of the faces produced by the decrements, either among 

 themlelves or on the primitive faces, having no idea that 

 tlrere could be any uncertainty in regard to a form which 

 prefented in fo fenhble a manner the appearance of a cube ; 

 and the more fo as the facets by which it was modified pre- 

 vented the difference from being obferved. He perceived 

 that this form was a real rhomboid fimilar to that of volcanic 

 iron ; and in that cafe, this law, which had appeared fo 

 lingular on the hypothecs of a cube, gave place to a ilmple 

 law, and every tiling, as we may fay, was reduced into 

 proper order. 



Jit regard to the varieties of the iron of the ifland of Elba, 



he 



