842 ON THE PRIMITIVE FORM OF CRYSTALS. 



Tabular Comparison of Hauy's Primitive Forms, with Mohs's 

 Fundamental Forms, and the Classes derived from the num- 

 ber of Axes of Double "Refraction. 



Optical Sys- 

 tem. 



I. — Crystals with 

 one axis of Dou- 

 ble Refraction. 



, II.— Crystals with 



I TWO AXES Of DOU- 



t ble Refraction, 



Ill—Crystals with 

 three Rectangu- 

 lar axes in a state 

 of equilibrium, & 

 therefore produ- 

 cing no double 

 refraction. 



It appears from this Table, that the First Class 

 of the Optical System includes Mohs's first and 

 second systems of fundamental forms. Although 

 the system of crystallizations deduced from these 

 two forms appears at present to be different, yet 

 we think that some mode of connecting them 

 together may still be discovered. The rhomboidal 

 and the pyramidal systems resemble one another, in 



Hauy's Primitive Forms. 



1. Rhomboid, 



I Ubtuse, ~| 

 9 ( Acute, f 

 !exaedral Prism, f 

 al Dodecahedron, j 



2. Regular Hexaedral 



3. Bipyramidal 



4. Octohedron, f With a square ) 



5. Right Prism, \ base, j 



6. Right 

 Prism, 



r Base a Rectangle, 

 J Base a Rhomb, 

 ~\ Base an oblique 

 parallelogram, 



T. Oblique 

 Prism, 



par- 



— « . j f Base a Rectangle. 



8. Octohedron, | BaseaRhomb - 



9. Cube. 



10. Regular Octohedron, 



11. Rhomboidal Dodecahedron, 



Mohs' Fundamen- 

 tal Forms. 



I. — Rhomboidal ? 



System, 



II. — Pyramidal 

 System, 



III. — Prismatic 

 System, 



IV — Tessular 

 System, 



