346 PHILOSOPHICAL TKANSACTIONS. [aNNO 1747. 



coat. The first sort may be considered as of the pebble kind ; and they are said 

 to be found near the beds of rivers, after great rains ; the others are found in 

 mines, and in the clefts of rocks. 



The gems of the first sort were what the ancients most usually engraved on : 

 these are commonly called intaglios; and they are mostly of a long oval figure, 

 inclining to a point at each end, convex as well on the engraved face as on the 

 others, with a ridge nmning from end to end on the outer side, which is thus as 

 it were divided into two faces; both which are also, though not so distinctly, 

 parted from the upper face, by another ridge running quite round the oval. 



The stone most commonly fovmd engraved is the beryl; the next is the plasm 

 or prime emerald; and then the hyacinth or jacinth. The chrysolite is some- 

 times, but rarely, found engraved ; as are also, but that very seldom, the crystal, 

 or oriental pebble, the garnet, and the amethyst. 



Of the beryl there are three species ; the red, inclining to orange-colour, trans- 

 parent and lively; the yellow, of an ochre-colour; and the white, commonly 

 called the chalcedon, of the colour of sheer milk. These last two have less life 

 than the first. 



The plasm or prime emerald is green, nearly of the colour of stagnated water, 

 sometimes tolerably clear, but for the most part full of black and white specks, 

 and rather opaque. — The jacinth is of a deep tawny red, like very old Port wine, 

 but lively and transparent. — The chrysolite is of a light green grass colour, and 

 is supposed to have been the beryl of the ancients, transparent, but not lively. — 

 The crystal, or oriental pebble, is harder and more lively than the common rock 

 crystal ; is of a silverish hue, and but very little inferior to the white sapphire. — 

 The garnet is of the same colour as the jacinth, but more inclining to the purple, 

 and not so lively. — The amethyst is of a deep purple, transparent and lively. 



There were some other species of stones engraved on by the Romans; l^^t 

 rarely before the latter times of the empire, when the art itself was greatly on 

 the decline. All the beforementioned sorts of stones are said to have been of the 

 produce of Egypt, or of the East Indies; and to have been brought from the 

 borders of the Nile, or of the Ganges. 



Here follows a general table of what are usually called precious stones. 



The beryl is red, yellow, or white. — ^The plasm is green. — The jacinth of a 

 deep tawny red. — The chrysolite of a light grass green. — The crystal, or oriental 

 pebble, of a silverish white. — The garnet of a deep red claret-colour. — The ame- 

 thyst, purple. — The diamond, white. — The ruby, red or crimson-coloured. — 

 The emerald, of a deep green. — The aqua marina, of a bluish sea-green, like 

 sea-water. — The topaz, of a ripe citron yellow. — The sapphire, of a deep sky- 

 blue, or of a silver white. — The cornelian, red or white. — The opal, white and 

 changeable. — The vermillion-stone, is more tawny than the jacinth. 



