436 Scientific Intelligence. 
between an hexagonal and a rhombic form arise from a slight 
perfect hexagonal form, and, fundamentally, may 
not the only crystallographic difference be that, in consequence of 
i f 
ders, and a nearly uniaxial structure at the center, where there is 
an obvious interpenetration between the individuals of the macle, 
QR et 
they have passed wholly unnoticed hitherto. Every one who - 
become familiar with the optical properties of crystals must have 
noticed that, with many always regarded as uniaxial, there 1s not 
these irregularities, although long known, have never been 
ined. They ha 
phenomena, seen with sections of crystals of tourmaline, corundum, 
or phenacite. One other illustration of our theory. : 
* See also Dana’s System of Min., 5th ed., figs. 154, 155, p. 156. 
