The value of diamonds is ascertained by their weight in carats; and this value increases, in a very high ratio, according to their magnitude. For instance, a diamond weighing one carat will be worth about 10_l._ whilst another of five carats will be worth 150_l._ and of ten carats 800_l._[2] This rule, however, can only be taken for diamonds of twenty carats and under. The larger ones, in consequence of the scarcity of purchasers, are generally disposed of at prices greatly inferior to their estimated worth. The value of some diamonds that are peculiarly perfect exceeds the above ratio; whilst, for a stone that is cloudy, foul, or of bad colour, even three quarters of the estimated value will perhaps be deducted. Footnote 2: A Carat is equal to four jeweller’s grains, seven grains of which are equal to six grains troy. To ascertain the value of wrought diamonds the weight must be doubled, about half being supposed to be lost in the working. This sum must be multiplied into itself, and the product by two. Thus to find the value of a diamond of twenty carats 20 × 2 = 40 × 40 = 1600 × 2 = 3,200_l._ No diamonds are so valuable as those that are perfectly transparent, and of snow─white colour. The green and yellow varieties are, however, much esteemed: the blue kinds were formerly more valued than at present; and the least valuable are those that have a grey or brownish tint. Black diamonds are much prized by collectors. The principal use of the diamond is in jewellery. It is also used by lapidaries, for slitting hard stones, and for cutting and engraving upon other gems; by clock─makers in the finer kinds of clock─work; in the glass─trade for squaring large pieces or plates of glass, and among glaziers for cutting their glass. The largest diamond ever known (if it be such, and not a white topaz, as some people have imagined) is in the possession of the Queen of Portugal, and weighs 1,680 carats, or more than _eleven ounces_. It was found in Brazil, and sent to Lisbon in the year 1746. It is still uncut, and has been valued at 5,644,800_l._ The Rajah of Mattan, in the island of Borneo, possesses a large diamond, shaped like an egg, with an indented hollow near the smaller end. It was found in that island about eighty years ago, is said to be of the finest water, and to weigh 367 carats, or more than two ounces and a quarter. Several years ago the Governor of Batavia, desirous of purchasing this gem, sent a Mr. Stuvart to the Rajah, authorizing him to offer for it 150,000 dollars, two large brigs of war, with their guns and ammunition, together with a certain number of great guns, and a quantity of powder and shot. The Rajah, however, refused to deprive his family of so valuable an hereditary possession; for the Malays not only attach to it the miraculous power of curing all diseases by means of water in which it is dipped, but also believe that the fortune of the family is sustained by its continuing in their possession.