72 03ST THE PRIMITIVE FORMS OF CRYSTALS. 



the solid, and having their intensity proportional to 

 the length of these axes, then in the obtuse octa- 

 hedron, where the principal axis of the solid is 

 shorter than the rest, we shall have the resultant 

 axis coinciding with it, and equal to either of the 

 other axes, but of an opposite character at the com- 

 mencement of the series of obtuse rhomboids. The 

 character of the resultant axis will continue the 

 same, and its intensity will diminish as the rhom- 

 boid becomes less obtuse, and when it becomes the 

 regular octohedron, by all the three axes becoming 

 equal, the three axes of polarisation will be in 

 equilibrio, or destroy each other. The series of acute 

 octohedrons now commences : The principal axis 

 of the solid is larger than the other two, and 

 therefore the resultant axis reappears, but with an 

 opposite character, and gradually increases as the 

 rhomboid becomes more acute, 



The other hypothesis consists in supposing the 

 axes to be four in number, and to be of the same 

 intensity, but placed at right angles to the four 

 faces of the pyramid. At the commencement of 

 the obtuse series, these axes will be parallel to one 

 another, and will form a resultant whose intensity 

 is 4s f 9 and of the same character as the separate 

 axes. As the octohedron becomes less obtuse, 

 the inclination of the separate axes to the re- 

 sultant increases, the intensity of the latter di-? 

 minishing, and its character remaining the same. 

 When the inclination becomes 54° 44' S", which takes 



