Virtual focus
Virtual Vir"tu*al (?; 135), a. [Cf. F. virtuel. See {Virtue}.] 1. Having the power of acting or of invisible efficacy without the agency of the material or sensible part; potential; energizing. [1913 Webster]

Heat and cold have a virtual transition, without communication of substance. --Bacon. [1913 Webster]

Every kind that lives, Fomented by his virtual power, and warmed. --Milton. [1913 Webster]

2. Being in essence or effect, not in fact; as, the virtual presence of a man in his agent or substitute. [1913 Webster]

A thing has a virtual existence when it has all the conditions necessary to its actual existence. --Fleming. [1913 Webster]

To mask by slight differences in the manners a virtual identity in the substance. --De Quincey. [1913 Webster]

{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 of refraction, appear to issue; the point at which converging rays would meet if not reflected or refracted before they reach it.

{Virtual image}. (Optics) See under {Image}.

{Virtual moment} (of a force) (Mech.), the product of the intensity of the force multiplied by the virtual velocity of its point of application; -- sometimes called {virtual work}.

{Virtual velocity} (Mech.), a minute hypothetical displacement, assumed in analysis to facilitate the investigation of statical problems. With respect to any given force of a number of forces 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 indefinitely near to the first, to which the point is conceived to have been moved, without disturbing the equilibrium of the system, or the connections of its parts with each other. Strictly speaking, it is not a velocity but a length.

{Virtual work}. (Mech.) See {Virtual moment}, above. [1913 Webster]

The Collaborative International Dictionary of English. 2000.

### Look at other dictionaries:

• virtual focus — n a point from which divergent rays (as of light) seem to emanate but do not actually do so (as in the image of a point source seen in a plane mirror) * * * the point at which divergent rays would intersect if prolonged backward …   Medical dictionary

• Virtual focus — Мнимый фокус …   Краткий толковый словарь по полиграфии

• virtual focus — noun 1. : a point from which divergent rays (as of light) seem to emanate but do not actually do so (as in the image of a point source seen in a plane mirror) 2. : a point toward which convergent rays are directed but which being intercepted they …   Useful english dictionary

• Virtual jury research — is a technique used by lawyers to prepare for trial.For many decades, attorneys have employed jury consultants to conduct jury research to help prepare for trial. The goals of such research vary: to assess the case and to discover its primary… …   Wikipedia

• Virtual — Vir tu*al (?; 135), a. [Cf. F. virtuel. See {Virtue}.] 1. Having the power of acting or of invisible efficacy without the agency of the material or sensible part; potential; energizing. [1913 Webster] Heat and cold have a virtual transition,… …   The Collaborative International Dictionary of English

• Virtual image — Virtual Vir tu*al (?; 135), a. [Cf. F. virtuel. See {Virtue}.] 1. Having the power of acting or of invisible efficacy without the agency of the material or sensible part; potential; energizing. [1913 Webster] Heat and cold have a virtual… …   The Collaborative International Dictionary of English

• Virtual moment — Virtual Vir tu*al (?; 135), a. [Cf. F. virtuel. See {Virtue}.] 1. Having the power of acting or of invisible efficacy without the agency of the material or sensible part; potential; energizing. [1913 Webster] Heat and cold have a virtual… …   The Collaborative International Dictionary of English

• Virtual velocity — Virtual Vir tu*al (?; 135), a. [Cf. F. virtuel. See {Virtue}.] 1. Having the power of acting or of invisible efficacy without the agency of the material or sensible part; potential; energizing. [1913 Webster] Heat and cold have a virtual… …   The Collaborative International Dictionary of English

• Virtual work — Virtual Vir tu*al (?; 135), a. [Cf. F. virtuel. See {Virtue}.] 1. Having the power of acting or of invisible efficacy without the agency of the material or sensible part; potential; energizing. [1913 Webster] Heat and cold have a virtual… …   The Collaborative International Dictionary of English

• virtual work — Virtual Vir tu*al (?; 135), a. [Cf. F. virtuel. See {Virtue}.] 1. Having the power of acting or of invisible efficacy without the agency of the material or sensible part; potential; energizing. [1913 Webster] Heat and cold have a virtual… …   The Collaborative International Dictionary of English