[ *£3 3 



£ X . On the Theory of the StruP.ure of Cnfals, ly the Alb <s TJa U\\ 

 From Vol. XF1I. of the Annates de Chimic. 



[Continued from Page 46.] 

 2. Various Examples of Deere,? /<• on the Edges. 



'QDECAEDRAL Sdphure of iron or martial pyrites 

 T9, Piatt* VI.) Pyrites Kre/tgi-:e!//es dod eei \dres. Dau- 

 i. Tab. Miner, edit, 179s, p. 29, De l'Ifle, Cnjhillor 

 graphic, t. ii. p. 224. var. 16. 



Geomet. Chara£i. Inclination of any one of the pentagons, 

 fuch a? DPRFSto the pentagon C P II G L, having the 

 (ame bafe P R 126' 56' 3 . Angles of the pentagon 

 CPRGL, L=i*i<J #' i 7 w s C or G= 106^ 25 ' 57'/ 30"; 

 P or R = io:r 36' 19". 



Let us again conceive a cubic nucleus, the different edges 

 pi which are fo many lines of departure to the lame number 

 pf decrements, taking place at the fame time in two differ- 

 ent ways, that is to fay, bv the fubtra&ion of fc\vp.ranges 

 parallel to the edges A B, C D {Jig, 7, Plate II.*), and of 

 one range parallel to the edges A D, B C. Let us fuppofe 

 alfo that each lamina, being in thicknefs equal only to a 

 fmall cube of the fide A B and C D, is equal to double the 

 fide of A D and B C. This difpofition, in regard to the de- 

 crements proceeding from the lines DC, B C (Jig. 7), is 

 represented by Jig . 14. In this hypothecs it is evident that 

 on account of the more rapid decreafe in departing from 

 D C or A B, than in departing from B C or A D, the faces 

 produced in the former cafe will be more inclined to the 

 plane A B C D, while the fact's produced in the latter will 

 remain as it were behind ; i'o that the pyramid will no 

 longer be terminated by a fingle cube K (Jig; 12), which; on 



All tlic'v '■)-•: below 14 referred to in this article will be fuvml ip 

 pl-itc- II of the preceding number, and ;il! above it in plates VI and VII of 

 cnt nui 



account 



