LIBRA

, Balance, one of the mechanical powers. See Balance.

Libra is also one of the 48 old constellations, and the 7th sign of the zodiac, being opposite to Aries, and marked like a part of a pair of scales, thus <*>. The figure of the balance was probably given to this part of the ecliptic, because when the sun arrives at this part, which is at the time of the autumnal equinox, the days and nights are equal, as if weighed in a balance.

The stars in this constellation are, according to Ptolomy 17, Tycho 10, Hevelius 20, and Flamsteed 51.

Libra also denotes the ancient Roman pound, which was divided into 12 unciæ, or ounces, and the ounce into 24 scruples. It seems the mean weight of the scruple was nearly equal to 17 1/2 grains Troy, and consequently the libra, or pound, 5040 grains. It was also the name of a gold coin, equal in value to 20 denarii. See Philos. Trans. vol. 61, pa. 462.

The French livre is derived from the Roman libra, this being used in France for the proportions of their coin till about the year 1100, their sols being so proportioned as that 20 of them were equal to the libra. By degrees it became a term of account, and every thing of the value of 20 sols was called a livre.