64 TERMINOLOGY. . 78. 



a. b. c. 



1. 86 5G' 25". 56 15' 4". 3G 3 48' 31". 



2. 87 34' 49". 53 46' 42". 38 38' 29". 



3. 85 50' 23". 54 21' 34". 39 48' 3". 



A. B. C. 



1. 158 12' 48". 148 59' 50". 158 12' 48". 



2. J 52 20' 22". 1GO32'13". 152 20' 22". 



3. 162 14' 50". 154 47' 28". 144 2' 58". 



5. The first of these varieties occurs in dodecahedral 

 Garnet; the third in octahedral Fluor-haloide ; the se- 

 cond depends upon the second variety of the icositetrahe- 

 drons, . 7o. 133." 



CONSIDERATION OF THE CONNEXION AMONG SIMPLE FORMS, 

 AND OF THE RELATIONS, UPON WHICH IT DEPENDS. 



. 78. OBSERVATIONS. 



There exists a very remarkable connexion among 

 several simple forms, which depends not only upon 

 the kind, but also upon the relative dimensions of 

 these simple forms. 



It is a matter of fact, sufficiently demonstrated by nu- 

 merous observations, that certain crystalline forms are pe- 



* The preceding enumeration of the varieties of tessular 

 , forms, as occurring in nature, is by no means complete. 

 Several varieties of the digrammic tetragonal-icositetra- 

 hedron (. 74.), of the tetraconta-octahedroii (. 77-) and of 

 other forms, have already been observed ; for instance, in 

 octahedral Fluor-haloide, in dodecahedral Garnet, in hexa- 

 hedral Iron-pyrites, &c. but not with a sufficient degree of 

 accuracy. It is to be expected, that our knowledge of these 

 forms will be considerably enlarged by a more accurate ex- 

 amination of nature. 



