**E*qua"tion** (?), n. [L. *aequatio* an equalizing: cf. F. *'equation* equation. See Equate.]

**1.**

A making equal; equal division; equality; equilibrium.

Again the golden day resumed its right,
And ruled in just **equation** with the night.
*Rowe.*

**2.** Math.

An expression of the condition of equality between two algebraic quantities or sets of quantities, the sign = being placed between them; as, a binomial **equation**; a quadratic **equation**; an algebraic **equation**; a transcendental **equation**; an exponential **equation**; a logarithmic **equation**; a differential **equation**, etc.

**3.** Astron.

A quantity to be applied in computing the mean place or other element of a celestial body; that is, any one of the several quantities to be added to, or taken from, its position as calculated on the hypothesis of a mean uniform motion, in order to find its true position as resulting from its actual and unequal motion.

Absolute equation. See under Absolute. -- Equation box, ∨ Equational box, a system of differential gearing used in spinning machines for regulating the twist of the yarn. It resembles gearing used in equation clocks for showing apparent time. -- Equation of the center Astron., the difference between the place of a planet as supposed to move uniformly in a circle, and its place as moving in an ellipse. -- Equations of condition Math., equations formed for deducing the true values of certain quantities from others on which they depend, when different sets of the latter, as given by observation, would yield different values of the quantities sought, and the number of equations that may be found is greater than the number of unknown quantities. -- Equation of a curve Math., an equation which expresses the relation between the coordinates of every point in the curve. -- Equation of equinoxes Astron., the difference between the mean and apparent places of the equinox. -- Equation of payments Arith., the process of finding the mean time of payment of several sums due at different times. -- Equation of time Astron., the difference between mean and apparent time, or between the time of day indicated by the sun, and that by a perfect clock going uniformly all the year round. -- Equation clock ∨ watch, a timepiece made to exhibit the differences between mean solar and apparent solar time. *Knight*. -- Normal equation. See under Normal. -- Personal equation Astron., the difference between an observed result and the true qualities or peculiarities in the observer; particularly the difference, in an average of a large number of observation, between the instant when an observer notes a phenomenon, as the transit of a star, and the assumed instant of its actual occurrence; or, relatively, the difference between these instants as noted by two observers. It is usually only a fraction of a second; -- sometimes applied loosely to differences of judgment or method occasioned by temperamental qualities of individuals. -- Theory of equations Math., the branch of algebra that treats of the properties of a single algebraic equation of any degree containing one unknown quantity.

© Webster 1913.