64 ON THE PRIMITIVE FORMS OF CRYSTALS, 



symmetrical round O, will be in equilibrio, or de- 

 stroy one another at that point. 



A similar result will be obtained when the sepa- 

 rate axes are not in the same plane, but are all 

 equally inclined to the resultant axis, provided they 

 are equal, and symmetrically arranged round that 

 axes ; or, to view the subject in a still more general 

 aspect, the action of several separate axes, of the 

 same character, ^whatever be their intensity, or 

 their number, or their inclination, may be resolved 

 into one axis, either of the same, or of an opposite 

 character, provided the intensities, the inclinations, 

 and the directions of the separate axes are all sym^ 

 metrically related to the line which is the resultant 

 axis. 



In the First Class of Primitive Forms, the very 

 nature of the geometrical solids which compose it, 

 seems to limit them to a single axis, either real, or 

 resulting from several separate actions, 



In the Obtuse Rhomboid, the line joining the 

 obtuse summits is the only line which can be placed 

 symmetrically in the solid, and is at the same time 

 the axis of the crystal, and the axis of double re- 

 fraction. 



The line joining the acute summits of the Acute 

 Rhomboid, — the line joining the centres of the hexa- 

 gonal bases of the Hexaedral Prism, — the line join- 

 ing the summits of the two pyramids of the Octohe- 

 dron with a square base, — and the line joining 

 the apices of the two pyramids which compose the 



