Astronomy, the time when the sun enters one of the equinoctial points.

The equinoxes happen when the sun is in the equinoctial circle, and the days are equal to the nights throughout the world, which is the case twice a-year; namely, about the 21st of March and the 23rd of September, the former being called the vernal and the latter the autumnal equinox. See Astronomy, vol. iv., p. 14; and Precession of the Equinoxes.

Equipollence (aequus, equal, and pollere, part. of pollere, to be powerful), in Logic, an equivalence between two or more propositions; that is, when they signify the same thing though differently expressed. Such terms or propositions are said to be equipollent.

Equirria, in Antiquity, a festival said to have been instituted by Romulus, and celebrated with horse-races in the Campus Martius on the 27th of February, in honour of Mars.