Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/725

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certain, from the experiment mentioned by Dr. Jurm, that i fuch an exact union of rays is not always neceffary to dijlintt Fijian.

Hence the doctor divides difiin£i V'tfton into two fpecies, viz. into Vifion perfectly dijlin£l, or perfecl Vifion, and Vifion im- perfectly diflintl ; which he calls limply by the name of di~ Jiina Vifion. The former, is that in which the rays of each pencil are collected into a fingle phyfical, or fenfible point of the retina j the other fpecies, is that in which thofe rays oc- cupy fome larger fpace upon the retina, yet fo far as the object is diftinctly perceived.

Perfect Vifion in a given eye, and a given difpofition of that eye, depends only upon the diftance of the object ; it has no dependance upon the magnitude of the object ; but diftind Vifion, in a given eye, and a given difpofition of the eye ? de- pends upon the diftance and magnitude of the object jointly. There appearing therefore a real difference between perfect Vifion, and what we call diftinci Vifion, the learned doctor has enquired very particularly into the reafon why an object may be feen diftinctly without perfect Vifion ; for which we refer to his eflay at the end of Dr. Smith's Opticks.

VISITATION (Cycl.) — The Vifitation of the Virgin Mary is a feaft inftituted firft by pope Urban IV. in the year 1389. and ordained to be kept on the fecond of July. Ho fin. Lex. in voc.

Visitation is likewife an order of monks founded by Francis de Sales and his mother Chahtalfa. Id. ibid.

VISPELLIONES, among the Romans, were flaves who could not be manumitted. Pitifc.

VISTAMENTE, in the Italian mufic, is ufed to give notice to play, or fing, quick, brifkiy, &c.

VISTE, in botany, a name given by fome authors to the com- mon white mountain coralloides : it is the Lapland name for the fame plant; the rain-deer, and many other creatures feeding on it when all other vegetables are deftroyed.

VITA (Cycl. )— Vita longa, a name given by fome bota- nical authors to the piper Mthiopicum, or /Ethiopian pepper. Gen. Herb. p. 1335.

VITALBA, in botany, a name given by fome authors to the viorna, or traveller's joy, a tall climbing plant with white flowers, common in the hedges. Get. Emac. Ind. 2.

V1TALIA, a name given by fome authors to the cardiac me- dicines.

V1TALIS, in botany, a name given by fome authors to the common telephium, called in Englith Orpine, and live-long, from its quality of living and flourifhing a long time after it is taken from the root. Ger. Emac. Ind. 2.

VITEX, the chafe Tree, in botany, the name of a genus of trees ; the characters of which are thefe : The flower confifts of one leaf, and is, as it were, bilabiated, and tubular be- hind ; the piftil arifes from the cup, and is fixed in the man- ner of a nail to the hinder part of the flower ; this finally be- comes a roundifti fruit, divided into four cells, each contain- ing oblong feeds. ,

The fpecies of Vitex, enumerated by Mr. Tournefort, are thefe: 1. The Vitex, with broad ferrated leaves. 2. The Vitex, with narrower leaves, difpofed in the manner of thofe of hemp. 3. The narrow hemp-like leaved Vitex, with bluifh flowers. 4. The white flowered Vitex; and 5. The Vitex, with extremely narrow leaves. Tournef Inft. p. 603. See the article Agnus Cafius.

VITIFERA, in zoology, a name by which many have called the common cenanthe, a bird well known in England by the name of the wheat-ear ; and called in lorne places the fallow- finch and white-tail. See the article Wheat-£^.

VITILIGO, a difeafe frequent among the Arabians : it is the fame with what is otberwife called Alphas. Hofn. Lex. in voc. See the article Alphos, Cycl. hSuppl.

VITIS, the Vine, the name of a genus of plants; the charac- ters of which are thefe : The flower is of the rofaceous kind, and iscompofedoffeveral petals, arranged in a circular form; from the middle of the flower there arifes a piftil, which is furrounded by a number of ftamina ; this finally becomes a round, fucculent, or juicy berry, containing ufually four pear- fathioned feeds. See the article Vine. The fpecies of Vine enumerated by Mr. Tournefort, are thefe : 1. The common, or wild Fine. 2. The Corinthian, or cur- rant Vine. 3. The parfley Vine, or Vine with deeply laci- niated leaves. 4. The early Vine. 5. The damafk Vine. 6. The mufkatel, or Apian Vine. 7. The Pergulane Vine, with fruit of the fize and fhape of plums. 8. The African Vine. 9. The Allobrogic Vine. 10. The large bunched Vine, with white fweet and firm grapes. 11. The large bunched Vine, With redith, or blackifli fweet grapes. 12. The large bunched, with whitifh oval grapes. 13. The hairy Vine. 14. Theclimbing five-leaved Canada vine. 15. The maple- leaved Canada Vine. 16. The abutilon-leaved Canada Vine, with purple grapes. 17. The American Vine, with ferrated ivy-like leaves. 18. The round leaved American Vine, with blue cluftered grapes. 19. The great, trifoliate, American Vine, with fmall round grapes in large clufters. 20. The fmaller trifoliate American Vine, with larger turbinated grapes difpofed in clufters. 21. Thefow-bread leaved American Vine, Suppl. Vol. II.

With racemofe corymbi of black grapes. Tourn. Inft. p. 613. See the article Vine.

Vitis Idcea, the Whortle, in botany, the name of a genus of plants ; the characters of which are thefe : The flower con- fifts of one leaf, and is of the globofe campaniform kind. The piftil arifes from the cup, and is fixed in the manner of a nail to the hinder part of the flower ; the cup finally becomes a foft umbilicated berry, juicy, and containing fmall feeds. The fpecies of Vitis Idcsa, enumerated by Mr. Tournefort, are thefe: 1. The Whortle, with oblong crcnated leaves, and black fruit. 2. The IVhortle, with roundiib, and not cre- nated leaves, and with red fruit. 3. The long leaved white berry'd Whortle. 4. The great round leaved Whortle. 5 . The fweet-fcented Whortle of Ceylon. 6. The pyrqla- leaved Canada Whortle ; and 7. The myrtle-leaved Canada Whortle. Tourn. Inft. p. 608.

VITISALTUS, a word ufed by fome medical writers for the Chorea fanili Viti. See the article Vitus'* Dance.

VITRAOO, in botany, a fpecies of plants, refembling that of which the glafs is made. It is otherwife called Helx'tne. Hofm. Lex. in voc. See the article Helxine.

VITREA tabula, a name given by fome authors to the inter- nal table of the cranium.

VITREUS Humor, the vitreous humour of the eye. See the article Eye.

VITRIOL (Cycl. ) — The manner of making the common green Vitriol, or copperas, at Bricklefy in Eftex, is this : They ga- ther the pyrites, or copperas ftone on the mores of Shepey- Ifland, and in other places; and this they lay upon a large bed, or floor prepared in the open air, underneath which there are gutters, or troughs difpeifed to receive and carry away the liquor impregnated with the mineral, to a ciftern where it is kept till worked.

The air and weather difTolves, and breaks thefe ftones ; and the rain falling on them, wafhes gradually out all the Vitriol ; which is thus feparated from it: they boil the liquor in large leaden pans, putting in a great quantity of old iron, and when fufliciently evaporated, they let it out into troughs, where the Vitriol feparates itfelf, and cryftalizes, fticking to the fides of the troughs, and to fticks and bars placed acrofa them. The remaining liquor they call the mother of Vitriol, and fave it to be afterwards boiled and evaporated again. Ray's Englifh Words, p. 139,

There is contained in the original liquor, of which Vitriol is made from the pyrites, a white, acrid, and pungent fait. This is feparated from the mother liquor, or brine, when no more Vitriol will Ihoot ; and is called by the chemifts, the faline principle of Vitriol.

Common green Vitriol, when diflblved in water, and fepa- rated from its metalline, and ochreous, or earthy particles, by zink, or any other of the imperfect metals, added in filings to the folution, is then much of the nature of this white fait, called the faline principle : it is white, not green, more unc- tuous than the common Vitriol, and has a grain rather appear- ing like nitre than like Vitriol.

The native white Vitriol of Goflelaer has alfo fomewhat of this nature in it, having lefs metal, and much lefs mineral fulphur than the common green, or blue Vitriols. The com- mon Vitriol, thus feparated from its earthy and metalline parts, will yield its fpirit eafily, and with the gentle heat of a fand furnace ; as the white fait extracted from the mother liquor of Vitriol will: whereas, in the common Vitriol, the metalline part fo detains the faline, that it cannot be driven of? in form of vapour, till that compages is broken, by a very intenfe and violent heat ; what remains in the retort after the diftillation of either this or the other fait, is not red like colcothar of Vi- triol, but is white and fpungy, and rather refembles burnt alum, than any other fubftance, in its appearance. It is infipid when firft taken out of the veflel ; but on being expofed to the air, it receives ftrange impreflions and alterations. Phil, Tranf, N°. 103. See the article Saline Principle. There is great reafon to believe, that Vitriols are no other than metals of different kinds, penetrated and reduced into a new form by fulphur. If thin plates of copper be cemented with beds of brimftone between, and the operation repeated four or five times with frefh brimftone every time, moft of the copper will be converted into Vitriol; and this diflblved in water, filtrated and cryftallizcd, will afford elegant rhom- boidal blue cryftals, no way diftinguifhable from common blue Vitriol.

The fame procefs may be repeated with iron inftead of copper, and the Vitriol will then be the common green kind, or cop- peras ; or if the acid liquor, called fpirit, or oil of fulphur by the bell, be rubbed on plates of iron or copper, and fuffered to dry away in the air, or over a gentle heat, and this repeated three or'four times, the metal being afterwards put into water, will be fo far corroded and diflblved by it, that there will be a liquor produced, which will yield, on a proper evaporation, blue orgreencryftals,accordingas iron or copper havebeen ufed. This fhews evidently, that the metal thus corroded by the acid of Vitriol, is foluble in water, fo far as it has been fo corroded ; and that this folution affords true Vitriol. Such may be the formation of Vitriol about the copper mines in many countries, and fucli the formation of the common green Vi- 5 1 trkl