precisely the same as if the stone were uniformly coloured, because all the light emerging from the stone has passed through the spot at the base and therefore been tinted blue. The mechanism employed in the fashioning of gem-stones is simple in character, and comprises merely metal plates or wheels for slitting, and discs or laps for grinding and polishing the stones, the former being set vertically and rotated about horizontal spindles, and the latter set horizontally and rotated about vertical spindles. Mechanical power is occasionally used for driving both kinds of apparatus, but generally, especially in slitting and in delicate work, hand-power is preferred. In the East native lapidaries make use of vertical wheels (Plate XIII) also for grinding and polishing stones, which explains why native-cut stones never have truly plane facets; it will be noticed from the picture that a long bow is used to drive the spindle. Owing to the unique hardness of diamond it can be fashioned only by the aid of its own powder. The process differs therefore materially from the cutting of the remaining gem-stones, and will be described separately. Indeed, so different are the two classes of work that firms seldom habitually undertake both. The discovery of the excellent cleavage of diamond enormously reduced the labour of cutting large stones. A stone containing a bad flaw may be split to convenient shape in as many minutes as the days or even weeks required to grind it down. The improvement in the appliances and the provision of ample mechanical power has further accelerated the process and reduced the cost. Two years were occupied in cutting the diamond known as the Pitt or Regent, whereas in only six months the colossal Cullinan was shaped into two large and over a hundred smaller stones with far less loss of material. Although the brilliant form was derived from the regular octahedron, it by no means follows that, because diamond can be cleaved to the latter form, such is the initial step in fashioning the rough mass. The aim of the lapidary is to cut the largest possible stone from the given piece of rough, and the finished brilliant usually bears no relation whatever to the natural octahedron. The cleavage is utilized only to free the rough of an awkward and useless excrescence, or of flaws. Although the octahedron is one of the common forms in which diamond is found, it is rarely regular, and oftener than not one of the larger faces is made the table.