Virtual Defined

According to the Oxford English Dictionary "virtual" has had numerous meanings, the most relevant for our inquiry are the following:

That [which] is so in essence or effect, although not formally or actually; admitting of being called by the name so far as the effect or result is concerned.

Optics. Applied to the apparent focus or image resulting from the effect of reflection or refraction upon rays of light.

Computers. Not physically existing as such but made by software to appear to do so from the point of view of the program or the user; spec. applied to memory that appears to be internal although most of it is external, transfer between the two being made automatically as required.

1. a. Possessed of certain physical virtues or capacities; effective in respect of inherent natural qualities or powers; capable of exerting influence by means of such qualities. Now rare.

1398 Trevisa Barth. De P.R. xix. viii. (Bodl. MS.), But vertual li3t igadered in a litel place or in a pointe is cleped moche li3t.
1477 Norton Ord. Alch. v. in Ashm. (1652) 62 But our chiefe Digesture for our intent, Is virtuall heate of the matter digerent.
A. 1593 Marlowe Hero & Leander iii. 89 So to all objects..his senses' flame Flowd from his parts with force so virtuall, It fir'd with sence things weere insensuall.
1626 Bacon Sylva §326 See if the Virtuall Heat of the Wine, or Strong Waters will not mature it;
1657 R. Ligon Barbadoes (1673) 106 Though the virtual beams of the Sun, give growth and life to all the Plants and Flowers it shines on.
1675 E. Wilson Spadacrene Dunelmensis Pref., Even ordinary water admits of a virtual mixture at least, as Experience evidenceth in Chalybeate waters.
1898 Meredith Odes Fr. Hist. 91 It was the foreign France the unruly feared,..Not virtual France, the France benevolent, The chivalrous.

b. Of herbs: Possessing specific virtues. rare.

1660 F. Brooke Le Blanc's Trav. 364 To Rivers they sacrifice the shels that come from them, to fountains fruits and vertual herbs.
1830 T. Aird Captive of Fez iii, She knew..every virtual plant, and every sovereign flower Beneath the moon.

2. Morally virtuous. Obs.

C. 1425 Wyntoun Cron. vii. 1218 His awyn oysse to lif wertual, May mirroure and ensample be Til alkyn statis.
C. 1425 Wyntoun Cron. vii. viii. 2206 Iohun of Salerne, prest cardynale, Commendit a lorde wertuale.
1607 Dekker Wh. of Babylon Wks. 1873 II. 216 You by your heauenly Influence change his vilenes Into a vertuall habit fit for vse.

3. a. Capable of producing a certain effect or result; effective, potent, powerful. Obs.

1432-50 tr. Higden (Rolls) II. 177 For a man and the worlde be assimilate in iij. thynges, in dimension diametralle.., in disposicion naturalle, and in operation virtualle.
1432-50 tr. Higden 185.
1526 Pilgr. Perf. (Pynson) iii. ix. 47 b, That is called after Saynt Thomas virtuall attencyon which causeth a person in the begynnyng of his prayer to haue an actuall consideracion of the prayer or duety that he hath to do.
1619 W. Sclater Exp. 1 Thess. (1630) 37 So vertuall was the speech of Paul a Prisoner, in the heart of his Judge.
1640 Shirley Arcadia iv. iii, I meant it A draught for false Zelmane, it being virtual To increase affection.
1672 Josselyn New Eng. Rarities 12 The Loone is a Water Fowl, alike in shape to the Wobble, and as virtual for Aches.
1683 Moxon Mech. Exerc., Printing i, Dr. a vertual Proof of his own Learned Plea, quotes two Authentique Authors.

b. Mech. (See quots.)

1815 J. Smith Panorama Sci. & Art II. 124 Whatever is the real length of the leg b a [of a siphon], the virtual or acting length when in use, only extends from b to the surface of the fluid.
1825 J. Nicholson Oper. Mech. 67 The velocity..due to a head of 15 inches; and this we call the virtual or effective head.

4. a. That is so in essence or effect, although not formally or actually; admitting of being called by the name so far as the effect or result is concerned.

1654 Jer. Taylor Real Pres. 21 We affirm that Christ is really taken by faith,..they say he is taken by the mouth, and that the spiritual and the virtual taking him in virtue or effect is not sufficient, though done also.
1664 Jer. Taylor Dissuas. Popery ii. §8 But even this attention is not necessary that it should be actual, but it suffices to be virtual;
1697 Burghope Disc. Relig. Assemb. 166 We shall find it to amount to no less than a vertual renunciation of our baptism.
1734 Waterland Diss. Exist. First Cause 30 Every Proof a priori proceeds by Causes either real or virtual.
1769 Burke Obs. Pres. St. Nat. Wks. 1842 I. 112 One part of it could not be yielded..without a virtual surrender of all the rest.
1787 Bentham Def. Usury viii. 73 Heading, Virtual Usury allowed.
1820 Milner Suppl. Mem. Eng. Cath. 132 To prevent the virtual choice of a Catholic Bishop by an A-Catholic Ministry.
1844 H. H. Wilson Brit. India III. 211 He had reigned thirty-three years, during the first ten of which he was virtual sovereign of the greater part of Hindustan.
1883 A. Barratt Phys. Metempiric 157 The simplest conscious action involves actual or virtual thought.

b. Virtual Church, a council or similar body acting in the name of the whole church. Also ellipt. as sb.

1646 J. Maxwell Burden of Issachar 20 Whatsoever power..the Catholike Church, or her virtuall and Representative, an oecumenical Councel, justly challengeth, this general Assembly vindicateth to it selfe.
1646 J. Maxwell Burden of Issachar 45 It was not consented to by the Church: that is, the Virtuall Church, the Generall Assemblie.
1654 Bramhall Just Vind. viii. (1661) 230 In all which..they understand..the virtual Church which is inuested with Ecclesiastical power, that is, the Pope with his Cardinals and Ministers.

c. Optics. Applied to the apparent focus or image resulting from the effect of reflection or refraction upon rays of light.

1704 J. Harris Lex. Techn. I, Virtual Focus, or Point of Divergence in a Concave Glass.
1728 Chambers Cycl., Point of Dispersion, is that wherein the Rays begin to diverge; usually call'd the Virtual Focus.
1808 J. Webster Nat. Philos. 185 They issued from the virtual focus in the axis of the lens.
1831 Brewster Optics i. 11 The point A', behind the called their virtual focus, because they only tend to meet in that focus.
1874 Lommel's Light 90 The lenses of the second group have virtual foci.

1831 Brewster Optics ii. 18 In convex mirrors the image is always a virtual one formed behind the mirror.
1859 Parkinson Optics (1866) 130 A familiar instance of a virtual image is that formed by a common looking-glass of an object in front of it:-the image of an object under water is virtual.
1885 Buck's Handbk. Med. Sci. I. 39/1 If their direction, after the refraction, be prolonged backward, their prolongations meet to form a virtual image.

d. Dynamics. Of velocity or moment (see quot. 1867). virtual displacement, any notional, infinitesimal displacement in a mechanical system that is consistent with the constraints of the system; virtual work, the work done by a force making a virtual displacement.

1818 Barlow in Encycl. Metrop. (1845) III. 41/1 [The] principle..of virtual now, by most foreign writers, made the foundation of the whole theory of statics.
1843 Penny Cycl. XXVI. 373/2 The name of the principle of virtual very ill fitted to express the idea which is to be conveyed. [Full account follows.]
1867 Thomson & Tait Nat. Phil. I. i. §237 If the point of application of a force be displaced through a small space, the resolved part of the displacement in the direction of the force has been called its Virtual Velocity;
1867 Thomson & Tait Nat. Phil., I. i. §237 The product of the force, into the virtual velocity of its point of application, has been called the Virtual Moment of the force;
1877 G. M. Minchin Treat. Statics iv. 61 The virtual work of a force is the product of the force and the projection along its direction of the virtual displacement of its point of application.
1897 A. E. H. Love Theoret. Mech. viii. 139 Principle of Virtual Work. The sum of the virtual works of all the forces on a system in equilibrium vanishes in every infinitesimal displacement.
1942 Synge & Griffiths Princ. Mech. ii. 60 Although the chief merit of the principle of virtual work lies in the fact that it does not involve the reactions of constraints, nevertheless it can be used to find these reactions should they be required.
1981 R. R. Craig Structural Dynamics ii. 28 Use the principle of virtual displacements to derive the equation of motion of the idealized system shown below.

e. Nucl. Physics. Applied to an excited state of an atomic nucleus which has energy in excess of that needed for the emission of a particle but a lifetime sufficiently long for it to be regarded as a quasi-stationary state.

1931 Proc. R. Soc. A. CXXXIII. 228 According to the theory..the emission of <alpha>- particles by radio active nuclei is to be explained by the assumption that there exists in the nucleus a `virtual' level of positive energy, which is occupied by an <alpha>- particle;
1955 I. Kaplan Nucl. Physics xvi. 368 Each excited state of the compound nucleus, whether bound or virtual, has a certain mean lifetime.
1963 W. E. Burcham Nucl. Physics ix. 372 All nuclear levels, except the ground state, can in principle emit radiation, leaving the nucleus in a less highly excited state, and virtual levels can in addition emit particles.

f. Particle Physics. Applied to particles and processes that cannot be directly detected and occur over very short intervals of time and space with correspondingly indefinite energy and momenta, which are not necessarily conserved within the time involved.

1949 Physical Rev. LXXV. 1305/2 These divergent terms must now be interpreted as renormalization or modification of the electric charge of the proton due to virtual mesons.
1961 W. S. C. Williams Introd. Elementary Particles xiii. 341 If the incident photon is 140 Mev and the positron is emitted at 90° with an energy of 100 Mev, then the four-momentum of this virtual electron is about 140 Mev/c;
1971 Sci. Amer. June 71/3 Although it may seem that virtual particles violate fundamental conservation laws, the violation is closely delimited to those areas where the uncertainty principle applies.
1973 L. J. Tassie Physics Elementary Particles viii. 15 The electron now consists of its `bare' self together with all its virtual interactions with the electromagnetic field, corresponding to the electron emitting and re-absorbing virtual photons.
1973 Sci. Amer. Oct. 110/1 The scattering of the two electrons is described by saying that these particles exchange a virtual photon that transfers momentum from one particle to the other.
1979 D. R. Hofstadter Gödel, Escher, Bach (1980) v. 146 To understand how a real, physical electron propagates..the physicist has to be able to take a sort of average of all the infinitely many different possible drawings which involve virtual particles.

g. Computers. Not physically existing as such but made by software to appear to do so from the point of view of the program or the user; spec. applied to memory that appears to be internal although most of it is external, transfer between the two being made automatically as required.

1959 Proc. Eastern Joint Computer Conf. xvi. 82/2 The sole function of the virtual memory is to increase machine speed.
1966 R. Adair et al. IBM Cambridge Scientific Center Rep. No. G320-2007 (title) A virtual machine system for the 360/40.
1966 IBM Systems Jrnl. V. 79 A virtual-storage computer (vsc) can decode addresses that are longer than those of its memory. The longer address is a virtual address that must be transformed to the actual, shorter memory address... The virtual addressing of the word in external storage triggers a procedure that automatically brings the addressed word into memory.
1972 Computer Jrnl. XV. 199/2 Our system runs in a virtual machine, which is implemented by an interpreter. We can therefore easily add new instructions to our virtual hardware, merely by extending the interpreter.
1973 P. B. Hansen Operating System Princ. i. 3 An operating system makes a virtual machine available to each user... The simultaneous presence of several users makes the virtual machines much slower than the physical machine.
1981 Pohl & Shaw Nature of Computation vi. 198 The Algolic language defines an Algolic virtual machine that may be implemented on a variety of computers. The Algolic machine could be constructed with the following software on a particular machine.
1982 G. Lee From Hardware to Software xxvi. 444 In a multi-programming system, several programs are being executed `at once'... Thus the operating system has to make available to each user a virtual store, of which he appears to be the sole user.
1983 80 Microcomputing Feb. 232/2 Virtual-memory systems have been prevalent in main-frames and large minicomputers for at least a decade.
1985 Which Computer? Apr. 54/1 No doubt this is a side effect of using the disc as a virtual memory.

h. Other collocations: virtual cathode (Electronics), a part of a space charge or electron beam where the potential is a minimum, so that electrons are repelled and positive ions attracted; virtual height, the height of an imaginary reflecting plane surface which in free space would give rise to the same travel time for reflected radio waves as an actual ionospheric layer; virtual temperature (Meteorol.) [tr. F. température virtuelle (Guldberg & Mohn Études sur les Mouvements de l' Atmosphère (1876) i. i. 6)] , the temperature that dry air would have to have in order to have the same density as a given body of moist air when at the same pressure.

1937 *Virtual cathode [see suppressor 3].
1964 New Scientist 1 Oct. 29/1 It was found that a virtual cathode could be obtained with a beam current of 3.5 milliamperes or more, and that its relaxation time was in fact inversely proportional to pressure.
1928 Proc. IRE XVI. 85 The heights as given in this paper are *virtual heights. They are calculated on the assumption that ordinary reflection takes place and that the layer is parallel to the earth's surface.
1967 [see ionogram 1].
1975 D. G. Fink Electronics Engineers' Handbk. xviii. 107 The reflection process for plane ionosphere is equivalent to mirror-type reflection at a height equal to the virtual height h' of reflection of the equivalent vertical frequency.
1910 C. Abbe tr. Guldberg & Mohn in Smithsonian Misc. Collections LI. No. 4. 124 We call the quantity T the *virtual temperature; for dry air the virtual temperature is the same as the absolute temperature.
1957 G. E. Hutchinson Treat. Limnol. I. vii. 468 C represents the virtual temperature of isothermal circulation prior to the development of stratification in the early summer.
1979 L. J. Battan Fund. Meteorol. v. 83 The effects of humidity can be taken into account by employing a quantity called the virtual temperature.

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