Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/710

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the aorta was found to be two foot long, and plainly of a fi- brous flefhyfubftance, for Uxor feven inches of its length; but from that downwards, it became only like clotted blood. At the time that this lady was moft violently afflioled with her afthma, the veins of her arms and neck were plainly per- ceived to have a pulfation wholly like that of the arteries, and plainly followed the motion of. the heart: She had, in the latter time of her life, ufually two of thefe fits in tour and twenty hours ; and when they were over, the pulfiitions in . the Veins ceafed. Mem. Acat 1. Par. 1704. Veins of plants, a term ufed by Ur, Lifter, to exprefs certain veflels in plants, which are analogous to the Veins of animals, and have been obferved in fome degree, by the naturaliils of almoft all ages, though differently defcribed by authors. Pliny has defcribed thefe parts of a plant under the names of vents and pulpts ; and Dr. Grew calls them .fibres- and infert- nients on the ligneous body, interwoven with that fubftar.ee which he takes to be the cortical body, that is, the .feveral diftinclions of the grain. This author alfo calls theni ! the. pores of the ligneous body; but that they are not merely fuch, may be plainly feen in cutting off a trani'verfe piece of the italic of fome large wild plant, as the great wild angelica, or the like. In the cut ftalk of this plant, the Veins every where fhew thcmfelves to be diftindt from fibres, "obfervable in- the parenchyma of the fame cortical body with theml'elves, the milky juice always rifmg befide the fibres 'not in any fibre: alfo in a tranfverfe cut of die root of the commonburdock, the like juice fprings on both fides of the feveral radii of the woody circle, that is, in the cortical body, and the pith only; Again, where there is no pith, there is none of this juice 60 be obferved, and confequently none of thefe Veins, as in the roots of plants, and trunks- of trees, but even in the bark of either. The fphondyliurn, the cicutaria, and many of: the thiftle kind, are inftanccs of this. Dr. Grew defcribes pores in the cortical body, and pith ; but thefe veffels are not of, the number of the things defigned by thofe .pores; thefe pores are extended by the breadth of the plant ;. but the pores of this juice are extended lengthwife. The pith of a dried fennel ftalk will fhew thefe very beautifully, and with due care, they may be traced all along the whole length of that pith. .It remains therefore, that if thefe are pores, they mufl: be of

. • thofe pores of the cortical body, that are fuppofed to be ex- tended the length thereof; but it is much more proper to call them Veins, or veflels, analogous to thofe of the human body,

, and covered with their proper membranes ; for they are to be found in the pith, and fometimes in the conical body of the plant, not included within the common tunicle of any fibres, but having their own proper membranes; which indeed, if

- they had not, the porous and fpungy' parts of the pith and cortex would be in all places filled alike with the juice ;■ but ■on the contrary, it is found to rife in a few fet and determinate ■: places only, that is, according to the difpofition and order of the veflels. If a ligature be made on the trunk of the fpurge, ?nd the trunk wounded, the juice burfts immediately oufin large quantities ; but if not wounded, none is difebarged by means of the ligature : now the exterior part of the trunk of thefe plants is allowed by all obfervers to be perforated in al- moft innumerable places ; and therefore, if this milky juice ■ were not contained in its peculiar veffels, there is nothinf to hinder, but it fhould ruftl out at thefe pores on the feature made above ; ,but it is evident, that it docs not do this till the containing veffels are wounded.

The juices of plarits are probably then all contained in thefe Veins, or diftina and proper veflels, covered with their own membranes, and not loofely diftributed through the fubftance of the plants. Thofe things which are effential to Vegetation, are alike allotted to all plants ; and it is to be fuppofed, that all plants have thefe veffels, though we cannot alike diftinguifh them in all. Thofe plants, whofe juices are white or yellow or of any other colour different from that of the body of th» trunk, are always diftbaiy feen, pouring out thofe juices at ieparate holes in a wound. Thofe whofe juices and ftalks are of the fame colour, do not fo readily fliew them ; but there is a tune when they are, in fome parts- of thefe plants, if not in ail, iuineiently plain to the naked eye

The tender (hoots of the greater and lefler maple, in May, are full of a milky ,u,ce, which is the known-liquor of thefe Veins ■ and if a clean knife-blade be applied to a tranfverfe cut of a young (hoot of elder, and then raifed gently away, the li- quor of thofe Veins will -be drawn up into firings, anfwering to the orifices of the Veins made by the wound. The pedicles of the leaves of our garden rhubarb, frequently Burnt out a fort of white and.tranfparent gum : this muft be an accidental exludationofa gum, very conftantly contained in the Veins of the plant, though not diltiuguifhable in thefe ftalks- this and many other like inftances, prove the exiftence of fuch •veffels, though they are not obvious to the eye ; and there re mams no doubt but .they ire to be found in all plants by fome trials Even the mufbrooms, the loweft clais of plants, are not deftitute of thefe veflels; there is one which fhews them very evidently, this is the wood mufhroom, whofe ftalk, When broken or cut, difcharges a milky juice, as hot as pep! per, or more fo; and tin's does not exfudate from the whole fpungy fubftance of the ftalk,- but is plainly difcharged from tile mouths of certain wounded veflels.

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The primary ufe of thefe Veins V, certainly to carry the w- tntious juice of plants ; and this appeal's plainly in that where they are not, there is no Vegetation, as is feen if an engrafted branch or arm is bared, or the clay, (hippy off; in this cafe all the courfe of the vegetation will appear to have been made only by the baik, the wood having had no (hare in it. The bark is the place where thefe Veins lie, not the wood; and therefore, it is no wonder, that the vegetation, if dependant on thefe Veins, is cairied on only where thefe Veins are. The vegetable drugs of our (hops are all of this nature, the juices- contained in thrfc Veins being evidently what «ive them their virtue. Phil.Tranf. N°. 79.

Vein, amongrniners, is that-fpace which is bounded with woughs,- and contains ore,- (par, qanck, clay, chut, croil, brown- hen, .pitsher- chirr, cur,-. which the pbiiofophers cail the mo- ther of, metals, and foinettrfles foil of all colours. When it bears ore, it is called a quick vein ; when no, ore, a.tleailvein. Hcuglito/i's Compl. Miner,, 111 the Explafl. of .the terms. The Veins of Mines difier.greatly from one another in depth length, and breadth ; fome (ketch obliquely, from the furiace toward the central parts' .of the earths slid thefe the miners tall deep Veins ; others lie (hallow, and circular, fo as ta.en- compafs a large fpae'e ; and thefe are 'termed, fpreadhv Veins 5 others poflels a great part of the fpaSe they lie in, both in length, and breadth; and thefe are called accumulated Veins, being no more than a fpace poiTeffed by a large group of fellh's of, one kind. To give the ccmpleat hiftory of Veins, and fibres which are fmaller, Veins, their differences, their directions, their intet'fhces, their dtfeontinuations,' their rifin?s and fail- ings, and their.goodnefs,- would be a large w.ork.° Let it be oberved, however, that thefe things .-feem all to proceed in a certain order, though that order, and the laws and rules of it, are not perfeftly underftood, fo as to affqrd fure directions for praflice ; whence it fometimes happens, that after a Vein has been fuccefsfully traced for fome time, it dips, breaks off, or takes a different courfe, leaving the workmen as it were at a fault.

When the Vein is found, a pit is to be funk upon it, and a crane fixed at the top of the pit for craning up the ore. Bur- rows, .or adits, are alfo to be cut horizontally through the hill in one or more places, reaching to the mine, and ferying to wheel out the ore, inftead of craning it up. Sbazu's Lefiurcs p. 246.

The manner of digging varies according to the nature of the Vein. If this be foft, it is dug with the fpade, and turned out into wooden trays, placed to receive it. If the Vein be harder it is to be knocked out with the hammer and chiflel. If it be too hard for this method, they foftenit by fire, which makes all (tones brittle ;. but the moft expeditious of all mine work- ing, is that by gunpowder, which tears up, and breaks to pieces vail rocks in a moment.

VELIT1S, in the natural hiftory of the antients, the name of a peculiar fort of fand ufed in the making glafs. The antients, in their different ages, made glafs of different materials. Thefe, however, were principally thin na- trum, which was, in moft refpeas, the fame tiling vyith our alkali falls ufed in glafs-making, mixed with flints, (hells, or fand. Sand was the moft univerfal mixture ; and for this pur- pofe, they always chofe fuch fand as was found waffled dean on the banks of rivers; and this they therefore called olafs- (and, or Velilis, oxbyalitis. Hill's Theoph. p. 11. "'

VELLA, in botany, the name of a genus of plants; the cha- raaers of which are thefe : The perianthium is of a cylin- dric figure, and erea, and is compofed of four (lender and obtufe leaves, which fall with the flower; the flower is compofed of four petals, and is of the .cruciform kind ; the petals are of an oval figure, and of the length of the cup ; the (lamina are fix filaments of the length of the cup, only two of them are a little fhorter than the other four ; thefe two (tend oppofite to one another ; the anthers are fimple ; the germen of the piflil is oval ; the ftyle is conic ; the ftigma is fimple ; the fruit is a globofe, criftated, pendu- lous pod, containing two cells, divided by a membrane, twice as large as the pod itfelf, and of an oval figure ; the feeds are roundifh. Linnai Gen. Plant, p. 317.

VELLIA, in zoology, a name ufed by fome authors for the lanius minor, or lanius tertius of Aldrovand, called in Eng- land the fw.Jher. Ray's. Ornithol. p. 54. See the article Fl u-

SHER.

VELOCE, in the Italian mtific, is ufed for quick VELOCISSAMENTE, or Velocissimo, in the- Italian mufic, is ufed for very quick, or with great rapidity. It is feldom met wkh ; prejio, or pre/fij/imo, being moftly ufed in its ftead. Broffard. '

VELOCITY, (Cycl.) — In the doarine of fluxions it is ufual to confider the Velocity with which magnitudes flow, or are generated. Thus, the Velocity with which a line flows, is the fame as that of the point, which is fuppofed to defcribe or generate the line. The Velocity with which a furface flows, is the fame as the Velocity of a given right line, that, by mov- ing parallel to itfelf, is fuppofed to generate arciai,?le. al- ways equal to the furface. The Velocity with which" a lolid flows, may be meafured by the Velocity of a given plain furface,

that