ON THE PRIMITIVE FORMS OF CRYSTALS. 71 



The following Table will shew the intensity of the 

 resultant axis in the Rhomboid for different incli- 



nations. 



Number of the se- Inclination of each separate Intensity and cha- 



parate axes. axis to the resultant axis. racter of the resul- 

 tant axis. 



Three -f axes, 0° 0' 3 + axes 



Three + axes, ...28° 8' 2 -faxes 



Three + axes, 41° 48' 1 + axis 



There + axes, 54° 44' 8 7 0 



Three + axes, . 70° 32' 1 — axis 



Three + axes, 90° 0' \\ — axis 



It is a singular circumstance, that all the crystals 

 in our table, which have the obtuse rhomboid, the 

 acute rhomboid, and the hexaedral prism for their 

 primitive form, have all a negative axis. Hence, 

 it will follow, if this axis is the resultant of three 

 axes, that in calcareous spar, bitter spar, carbonate of 

 lime and iron, and tourmaline, the three axes are ne- 

 gative, while in ruby, sapphire, corundum, cinnabar, 

 arseniate of copper, apatite, beryl, emerald, and ne- 

 pheline, the three axes are positive. 



A similar law takes place in the octohedral crys- 

 tals with a square base ; and the regular octohe- 

 dron forms the passage between the acute and the 

 obtuse octohedron, in the very sa ne manner as the 

 cube does between the acute and the obtuse rhom- 

 boid. In tracing this law, we may adopt either of 

 two hypotheses. If we consider the octohedral 

 crystals as having three rectangular axes of the 

 .same character, coinciding with the three axes of 



