development of its latent beauty; and that the result was not attained until Newton demonstrated the laws that govern the refraction of light. It is only in the brilliant and rose-cut forms, or their modifications, when made with mathematical precision, that the brilliancy and beauty of the stone is displayed in perfection. The ancients, therefore, were not acquainted with the full splendors of the gem. For, being ignorant of the laws of refraction of light, they polished the stone chiefly with the view of preserving its greatest weight; and, at the same time, producing perfect transparency. Hence most of the specimens of ancient and barbaric art are rudely cut, and therefore do not exhibit the degree of beauty which is latent in the mineral. This is also one of the reasons why the luxurious Romans preferred the opal to the diamond, since the polished, or even the rude specimens of opal exhibited their glorious reflections of wondrous hues, both by day and in artificial light by night; while the diamond, with its natural or polished faces, gave forth no prismatic display in the daylight, and but a slight degree comparatively in artificial light at night. Whence arises this remarkable brilliancy, and to what particular cause is the property due? This inquiry has afforded a fruitful theme of speculation among philosophers, but at the present time we are content to say that the refractive power of the gem is due to the nature of its substance. This is somewhat indefinite, it is true, but what else can we say?