VIRGO

, in Astronomy, one of the signs or constellations of the zodiac, which the sun enters about the 21st or 22d of August; being one of the 48 old constellations, and is mentioned by the astronomers of all ages and nations, whose works have reached us. Anciently the figure was that of a girl, almost naked, with an ear of corn in her hand, evidently to denote the time of harvest among the people who invented this sign, whoever they were. But the Greeks much altered the figure, with clothes, wings, &c, and variously explained the origin of it by their own fables: thus, they tell us that the virgin, now exalted into the skies, was, while on earth, that Justitia, the daughter of Astræus and Ancora, who lived in the golden age, and taught mankind their duty; but who, when their crimes increased, was obliged to leave the earth, and take her place in the heavens. Again, Hesiod gives the celestial maid another origin, and says she was the daughter of Jupiter and Themis. There are also others who depart from both these accounts, and make her to have been Erigone, the daughter of Icarius: while others make her Parthene, the daughter of Apollo, who placed her there; and others, from the ear of corn, make it a representation of Ceres; and others, from the obscurity of her head, of Fortune.

The ancients, as they gave each of the 12 months of the year to the care of some one of the 12 principal deities, so they also threw into the protection of each of these one of the 12 signs of the zodiac. Hence Virgo, from the ear of corn in her hand, naturally fell to the lot of Ceres, and we accordingly find it called Signum Cereris.

The stars in the constellation Virgo, in Ptolomy's catalogue, are 32; in Tycho's 33; in Hevelius's 50; and in the Britannic 110.

VIRTUAL Focus, in Optics, is a point in the axis of a glass, where the continuation of a refracted ray meets it. Thus, let D be the centre, and DBE the axis of the glass AB; upon which falls the ray FA. Now this ray will not proceed straight forward, as AH, after passing the glass, but will take the course AK, being deflected from the perpendicular AD. If then the refracted ray KA be produced, by AE, to the axis at E, this point E Mr. Molineux calls the Virtual focus, or point of divergence.