Vĭrt'ū-al, a.

(vĭrt'/yū-al), a. [Fr. virtuel, Pr., Sp., & Pg. virtual, It. virtuale, L. Lat. virtualis, from Lat. virtus, strength, power.]

1Sense 1. Having the power of acting or of invisible efficacy without the material or sensible part; potential. [Rare.]

Every kind that lives, Fomented by his virtual power, and warmed. Milton.

Neither an actual nor virtual intention of the mind, but only that which may be gathered from the outward acts. Stillingfleet.

2Sense 2. Being in essence or effect, not in fact; as, the virtual presence of a man in his agent or substitute. “To mark by slight differences in the manners a virtual identity in the substance.” De Quincey.

Principle of virtual velocities (Mech.), the law that when several forces are in equilibrium, the algebraic sum of their virtual moments is equal to zero. — Virtual focus (Opt.), the point from which rays, having been rendered divergent by reflection or refraction, appear to issue; the point at which converging rays would meet if not reflected or refracted before they reach it. — Virtual moment of a force, the product of the intensity of the force multiplied by the virtual velocity of its point of application. — Virtual velocity (Mech.), a minute hypothetical displacement, or motion, assumed in analysis to facilitate the investigation of statical problems. With respect to any given force of a number holding a material system in equilibrium, it is the projection upon the direction of the force of a line joining its point of application with a new position of that point conceived to be taken indefinitely near to the first, and without disturbing the equilibrium of the system, or the connections of its parts with each other.