in Chemidal ComlinaHons. 



191 



in number, and which has fifty-six triangular faces, of which 

 eight are equilateral and the other forty-eight are isosceles. 



If, instead of uniting the tetra-octohedron with a single octo- 

 hedron, we combine it with a tri- octohedron, by placing the six. 

 suinniits with four faces of the latter at the same point where 

 we have placed the six summits of the fifth octohedron in the 

 formation of tlie penta-octohcdron, we shall have the polyhedron 

 composed of seven equal octohedrons, to which I have given the 

 name of epta-octohedron, and whicli has forty-two summits and 

 eighty triangular faces, of which eight are equilateral, twenty- 

 four isosceleSj and forty-eight scalene. 



1 subjoin a comparative table of these twenty-three represen- 

 tative forms. 



Total 



of 

 (•'aces. 



Tptrahedron (1) 



Ociolifrlroii , 



Farallelopipedon ..,.2 0806006 

 Pri'-m hexahedron ....Oa 12 06203 



Dodecahedron ^ \ '^ ^'^' ^2 V2 



Hexri-deraht'droii .... 1 1 10 16 16 

 TrJacoiitahodron .... 2 2 «0 ?4 6 .SO 



Trioclohodron 3 IH 32 32 



Trapezoidal 2 3 20 21 24 



Tetra-liedron 4 16 2a 28 



Penta-tclraliedroti .... 5 20 12 12 24 

 Ilexa-tetrahedron .... 6 24 6 3 !) 14 

 Hexa-tctrahcdron pyramidatcd 6 1 30 24 a 32 

 Cubi)-!iexa-tetrahcdroii . . 8 3,' 48 6 54 



Amphihedron 8 1 38 24 24 48 



f'eniacontaliedron .... 6 2 o6 36 12 2 50 

 Octocontuhedrun .... 6 3 42 80 80 

 Octo-tetrahpdroa .... 8 32 6 12 18 

 I'ptacontalicdrijii .... 8 2 44 6+ 2 4 70 

 TrioctohiMlroii pyramidated . 8 S 50 48 24 72 

 I'eira-octohedroii .... 4 24 8 6 14 

 Pcnta-iictohefiron .... 5 30 56 56 

 I'pta-octohedron . . . . ( 7 42 80 [ 80 

 *,* Models of all these crystalline forms are executed with the greatest 

 accuracy under the direction of Mr. J. Mawe, No. 149, Strand, where 

 lliere are always to be found numerous suits of crystaK cut in wood, 

 aL;roeal)ly to Ilaiiy's system of crystallo;;raphy. Tliesc models, and the 

 small specimens in cahinets coiitainini; from 100 to 1000 arid upwards 

 ditferent minerals, which are sold by Mr. Mawe on very ruiisoniddc ttrms, 

 uccumpanicd with descriptive catulo;,'ucs, certainly present the easiest 

 and best means of acquiring a knowjedjjc of the sciences of crystallo- 

 ;;rapliy and mineralofiy, ami arc well worthy the attention not merely of 

 young students, but even of more experienced persons, in these somewhat 

 diflicult and appnrentlv arduous but pleasing studies. _ 



