The author, after alluding to the influence of compression and dilatation in producing the doubly refracting structure in solids of all kinds devoid of it, and in modifying it where it exists, mentioned that the phenomena to be described have no relation to those alluded to.

In experimenting on the double reflexion and polarization of light discovered by him in the chrysammates of potash, and magnesia, murexide, and other crystals, he found that they could be spread out on glass by hard pressure, like grease or soft wax; and that in the case of dark powders, he could thus obtain a transparent film, exhibiting double reflexion and polarization from its surface, as well as if it had been a large crystal.