Pliny entertained the same idea, and also that its infrangibility could be overcome only by first steeping it in goats’ blood. Even in mediæval times Ben Mansur, the Persian mineralogist, gravely states that a diamond laid upon the anvil and struck by a hammer would not be broken, but would be driven by the violence of the blow into the substance of the anvil. This stupid but wide-spread idea has prevailed even in modern times; and many a gem has been sacrificed by the ignorant in testing the character of the stone. The brittleness of the gem is partly due to its singular cleavage, which in regular crystals is so perfect and uniform as to permit the lapidary to remove the laminæ so as to entirely demolish the structure of the crystal. But when once accomplished, no artisan, however skilful, can replace them again. The facility with which the stone may be separated was known in ancient times among the Hindoos, and probably in Europe as early as the sixteenth century, as De Boot knew of a physician who could divide the diamond into thin scales like a piece of talc; but it was forgotten until Wollaston not many years ago stumbled upon the secret of cleavage and made it known to modern science. The real charm and value of the diamond lie in its remarkable brilliancy, and in the wonderful prismatic display of the bright and beautiful colors, which are constantly fugitive, but perpetually returning, as the learned Abbé Haüy elegantly expresses it. When a ray of light is reflected from the surface of a body, a particular impression is conveyed to the eye, which we may properly term the eclat. This impression is often so decided and so varied in its effects, that we are able to distinguish certain substances at a glance; and the reflection from the diamond exhibits a peculiarity which is seen only in a very few substances. This is known as the adamantine flash, and none of the gems display it to any marked degree except the rare zircon. We witness the perfection of this property in the black and opaque but crystallized diamond, when faceted by art; and also in some few minerals of which we shall soon make mention. When the rays of light are refracted, after passing through the transparent diamond after it has been cut in a certain manner, and its facets are arranged in an exact relation to each other, then we obtain the remarkable exhibition of color which is known as the prismatic display. This singular property is seen in perfection, or even to any considerable degree, only in the diamond, among all the gems thus far known. But art, however, has succeeded in imitating it in one of her productions of glass, and so admirably, that under favorable circumstances it is quite impossible for the eye alone to distinguish the artificial from the real gem. Some of the theories relating to the causes of these phenomena we will discuss hereafter, and at the present will only say that it is to modern science the diamond owes the full