According to Jaffries, the value of diamonds is in the duplicate ratio of their weights. Thus, if au uncut diamond of one carat be worth £2, that of one cut and polished would be valued at £8 sterling in the brilliant. A carat weighs four nominal grains, or 3.166 grains troy. At this rate a cut diamond of two carats would be 2 x8 x 2= £32 ; one of three, 3 x 8 x 3 =£72 ; one of four, 4x8X4=£128 ; and one of five, 5X8 x5=1,200. The rose diamond is of inferior value, but has been rated at £4 the carat when polished. For the purpose of estimating diamonds of inconsider able size, the jeweller employs a gauge, in the handle of which are embedded small crystals of various relative sizes, from ilath to ith of a carat, and a comparison is therewith made when there are numbers of various minute sizes. The rough diamond is called bort ; and points are those small fragments with naturally acute angles which are set in glaziers' cutting diamonds, and sell at £10 the carat.
Most precious stones will scratch, but diamonds alone cut glass. It is also employed for the lenses of microscopes. It has but little chromatic aberra tion, but the frequent irregularity of its structure is a drawback to its employment for this purpose.
There seems to have always been a considerable traffic in this precious stone, carried on by the mercantile body on the east coast of peninsular India. In Madras, up to about the year 1840,
what may be called the country transactions with England were conducted through European firms. The diamonds exported by them consisted of the small uncut stones, which were sent to London in packets called bulses ; and the mercantile character of the Messrs. de Fries of 3fadras stood so high in the London market, that their packets or bulses were sold there by weight without examination. Latterly, however, the export trade fell into the hands of the native community, amongst whom there is a considerable tendency to speculate on prices. The course of trade has thus been some what changed. Prices have risen at least 20 per cent.; and if Europeans do now engage in the business, it is chiefly in importing from London. — Tavernier's Travels, pp. 135 – 149 ; Sir S. Raffles' Hist. of Java ; Low s Sarawak ; Rennell's Memoir, pp. 233 – 290 ; Pennant's Hindustan ; Heyne's Tracts ; Captam Cullen ; Lt. Neu:bold ; Dalrymple's Repository ; Voysey's Journal ; Dana, Manual of Mineralogy ; Catalogue of Great Ex hibition of 1851 (Class xxiii.)• Eng Cyc. p. 323 ; Ainslie's Materia Medica ;_Slason's Tenasserim ; Powell's Handbook ; Tomlinson, p. 300 ; dlfr. Tennant in Illustrated London News, 31st January 1852 ; Crawfurd's Dict. p. 120 ; 11Iedlicott, Blatt ford, and Ball, Geology of _India.