virtual image 名詞
 假像,虛像


 Vir·tu·al a.
 1. Having the power of acting or of invisible efficacy without the agency of the material or sensible part; potential; energizing.
    Heat and cold have a virtual transition, without communication of substance.   --Bacon.
 Every kind that lives,
 Fomented by his virtual power, and warmed.   --Milton.
 2. Being in essence or effect, not in fact; as, the virtual presence of a man in his agent or substitute.
    A thing has a virtual existence when it has all the conditions necessary to its actual existence.   --Fleming.
    To mask 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 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.

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 Im·age n.
 1. An imitation, representation, or similitude of any person, thing, or act, sculptured, drawn, painted, or otherwise made perceptible to the sight; a visible presentation; a copy; a likeness; an effigy; a picture; a semblance.
    Even like a stony image, cold and numb.   --Shak.
    Whose is this image and superscription?   --Matt. xxii. 20.
    This play is the image of a murder done in Vienna.   --Shak.
    And God created man in his own image.   --Gen. i. 27.
 2. Hence: The likeness of anything to which worship is paid; an idol.
    Thou shalt not make unto thee any graven image, . . . thou shalt not bow down thyself to them.   --Ex. xx. 4, 5.
 3. Show; appearance; cast.
    The face of things a frightful image bears.   --Dryden.
 4. A representation of anything to the mind; a picture drawn by the fancy; a conception; an idea.
 Can we conceive
 Image of aught delightful, soft, or great?   --Prior.
 5. Rhet. A picture, example, or illustration, often taken from sensible objects, and used to illustrate a subject; usually, an extended metaphor.
 6. Opt. The figure or picture of any object formed at the focus of a lens or mirror, by rays of light from the several points of the object symmetrically refracted or reflected to corresponding points in such focus; this may be received on a screen, a photographic plate, or the retina of the eye, and viewed directly by the eye, or with an eyeglass, as in the telescope and microscope; the likeness of an object formed by reflection; as, to see one's image in a mirror.
 Electrical image. See under Electrical.
 Image breaker, one who destroys images; an iconoclast.
 Image graver, Image maker, a sculptor.
 Image worship, the worship of images as symbols; iconolatry distinguished from idolatry; the worship of images themselves.
 Image Purkinje Physics, the image of the retinal blood vessels projected in, not merely on, that membrane.
 Virtual image Optics, a point or system of points, on one side of a mirror or lens, which, if it existed, would emit the system of rays which actually exists on the other side of the mirror or lens.


 virtual image
      n : a reflected optical image (as seen in a plane mirror)