60	PRECIOUS STONES.
	the locust-tree, Ceratonia siliqua, weighs on the average 3-1/6 grains, and constitutes, no doubt, the true origin of the carat. The carat is not absolutely of the same value in all countries. Its weight, as used for weighing the diamond and other gem-stones in different parts of the world, is given, in decimals of a gram, by the majority of the authorities, as—
	Assuming the gram to correspond to 15.43235 English grains, an English diamond carat will nearly equal 3.17 grains. It is, however, spoken of as being equal to 4 grains, the grains meant being " diamond " grains, and not ordinary troy or avoirdupois grains. Thus a diamond grain is but 0.7925 of a true grain. In an English troy ounce of 480 grains there are 151-1/2 carats ; and so it will be seen that a carat is not indeed quite 3.17 grains, but something like 3.1683168 grains, or less exactly, 3.168 grains. Further, if we accept the value in grains of one gram to be, as stated above, 15.43235, and if there be 131-1/2 carats in a troy ounce of 480 grains, it will follow that an English diamond carat is 0.205304 of a gram, not 0.205409, as commonly affirmed. By recalculat­ing the value of the diamond carat, as used in different parts of the world, into its scientific equivalents in the metric system, the weight to four places of decimals will become, according to Mr. Lowis D'A. JacksonJ—