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Show VA Rarety of the Air is chiefly owing to the inreas’d or diminifh’d Preffure, by the Acculation or Exhauttion of fuperior Air, whilft Heat and Cold alter its Denfity in much lefs Proportion: The Clouds made of the Vapours above-mentioned, inftead of conforming them- felves to the alter’d Denfity of the ambient Air, will rife when it is condens’d, and fink when it is rarefied; and alfo rie or fink, when the Preflure of the Air is not alter’d, and its Denfity very little chane’d, by their own Dilatation, owing to Heat or Cold: As may be often obferv’d, by feeing them change their Height confiderably, whilit the Barometer continuesexactly at the fame Degree, and the Liquor of the Thermometer rifes or falls very little, and fometimes not at all. As for the Manner howClouds are chang’d into Rain, it has been hinted at the Be sinning ofthis Article ; but, for farther Satisfaction, let the Reader have Recourfe to Dr. Halley’s Account of it in the Pbilofophical Tranfattions, N° 183, which Dr. Defaguliers fays he has always found eable to the Phenomena. He adds, That fince he: had, for Brevity fake, only mention’d at what Heights. from the Surface of the Earth Zapours of different Denfities will come to an Ai quilibrium, without giving a Reafon for fettling the Place of Aquilibrium, at whofe Heights he thought it proper here to give the Method by which they may befound ; viz, As the Vapours will fettle and rife where the Airis of the fame Denfity with themfelves, it is only requir’d to find the Denfity of the Air at anyDiftance from the Earthat feveral Heights of the B Dr. Hall neler, which may be deduc’d trom two Tables, Philofopbical Tranf- aélion N° 386, (the firft fhewing the Altitudes to given Heights of the Mer 3 and the fecond, the E ghts of the Mercury again at given Altitudes) and knowing the Degree of Heat bythe Thermometer, becaufe the Den- fity of the Vapour depends upon the Degree of Heat of the » provided that proper Al- lowances be made for the great Rarefation of the Air near the Earth in hot and dry Weather, and the Condenfation ofthe Vapours in their Rife, by reafon of the Air being colder at a little Height above the Earth than juft at the Surfaceof it. 4 The Quantity of Vapour rais’d from the Sea by the Warmth of the Sunis far greater than one would imagine. Dr. Halley has attempted to eftimate ir. In an Experiment made with that View, and defcrib’d in the Philofophical Tranfaétions, he found that a Quantity of Water no warmer than Air in Summer, loft in Vapour, in the Space of two Hours, no lefs than sy Part of an Inchin Depth: Nowfor sy in two Hours, taking for the eafier Calculation, zz in the VA VA fquare, 4 Gallon; a Mile fquare, 6914 Tuns: a f{quare Degree fuppos’dof 60 Englifh Miles, will evaporate 33 Millions of Tuns; and if the Mediterranean Sea be eftimated at 410 Degrees long, and four broad, Allowa nces be- ing made for the Places whereit is broader, b thofe where it is narrower, there will be 160 fquare Degrees at Sea; and confequently the whole Mediterranean mutt lofe in Vapour, ina Summer’s Day, at leaft 5280 Millions of Tuns, In this Quantity of Vapour, tho’ very great, are only the Remains of another Caufe, which cannot be reduc’d to Rule; that is, the Winds, whereby the Surface of the Water is lick’d up, fometimes fafter than it exhales by the Heat of the Sun; as it is well knownto thofe who have confider’d thofe drying Winds. For the Manner wherein Vapoursare rais’d, fee more in Dew, Rain, Heat, Cold, and Ba- rometer. For the Effect of Vapours in Formation of Springs, fee Springs, &c. VARIEGATED, fignifies ftreak’d or di- verfify’d with feveral Colours. There are now a great Variety of Plants in the Gardens of the Curious, whofe Leaves are variegated with Yellow or White. Thofe which are {potted with either of thefe Colours in the Middle of their Leaves, Refrangibility, and the Magnitude ofits com- in the Plants, fince whenever they become vigorous, this Striping is either render’d lefs them, ponent Parts. _ 4. According to the firft Definition, Light is the Subje of Colour ; according to the latter it is the Agent. 5, So then, Light fometimes fignifies that Senfation occafion’d in the Mind by the View of luminous Bodies ; fometimes that Proper ty in the Colour oftheir Leaves, they do not in thofe Bodies, whereby they are fitted to growfo large as before, norare they fo capa- excite thofe Senfations in us. ble to endure the Cold ; fo that many Sorts of 6. Various are the Opinions of ancient and Plants which are hardy enough to endure the modern Author s, and ofthe feveral Seéts of Cold of our Climate in the open Air, when in Philofophers , with regard to the Nature and their natural Verdure, do require to be fhelter’d Origen of the Phenomenon Colour. in the Winter after they are become varie7. The Peripateticks affert Colours to be real aied, and are feldomof fo long Continuance ; Qualiti es, and inherent in the colour’d Bodies, which is a plain Proof that it is a Diftemper and fuppofe that Light doth vilible, orintirely thrown off; efpecially (as was before obferv’d) if the Plants are only blotch’d; the Edging be of a yellow Colour, it is t to remain than whenit is white ; which m’d the moft beautiful Striping, and (when once thoroughly eftablifh’d ) irdly ever to be got out of the Plants fo as to render the Leaves intirely fuch is the Venom of this morbid are call’d Blotch’d that it not only tinges the Leaves, Bark and Fruit of Trees are in- Leaves are edg’d with thefe Colours, are call’d are blotch’d, are generally fubjeé&t to become plain, when planted ina goodSoil, orat leaft in the growing Seafon, will have but fmall Appearance of the two Colours; but thofe which have edg’d Leaves, do rarely become plain again, efpecially if the Edging is broad, and goes quite through the Leaves; though thefe do not appear fo finely variegated in the growing Seafon, as they do the other Parts of the Year. All the different Sorts of Variegation in Plants were at firft accidental, being no more than a Diftemper in the Plant; which being obferv’d, has been cherifh’d by impoverifh- ing the Soil in which they grow, by which Methodtheir Stripes are render’d more lafting and beautiful. But whatever fome Perfons have affirm’d of ftriping Plants by Art, 1 could never obferve it done by any, unlefs in woody Shrubs and Trees; which may be vari gaied by putting in a Bud or Graft taken froma variegated Plant, where altho’ the Bu fhould not grow, yet if they keep frefh but eight or ten Days, theywill manytimes com- municate their gilded Mia/ina to the Sap ofthe Trees into which they were budded ; fothat in a fhort time after, it has appear’d very vifible in the next adjoining Leaves, and has been afterwards fpread over the greateft Pare of the twelve Hours that the Sun is up each Day, will raife +4 of an Inch from the Surfac it Tree: But in fuch Plants which are herbae of ceous, where this Operation cannot be péerthe Se _On this Suppofition, everyten fquare Inches f the Surface of the Wate r yield in Vapour fer Diem a Cubick Inch of Water of 4 Feet thofe Seeds gather’d from variegated Plants, there will conttantly be fome variegated Plants produc’d ; as in the Strip’d-wing Pea, the Greater Maple, 8c. fo that thefe may be conftantly propagated that Way. That this Striping proceeds ftom the Weaknefs of Plants is very evident, finceit is always obferv’d, that whenever Plants do alter thus (in the Gardener’s Term); but thofe whofe Sirip’d Plants: Thofe Plants whole Leaves form’d, th isno way yet afcertain’d whereby this Striping can be effe@ted by Art. : In fome Sorts of Plants this Diftemper 4s often communicated to the Seeds; fo that fr tnote VA as in the Orange, Pear, &c. Bark and Fruit are ftrip’d in the fame r as their Leaves. The different Colours which appear in Flowers do alfo proceedfrom the fame Caufe, ho’ it is generallyina lefs Degree in themthan } caves and Branches are infected: ious Colours which we fee in the fame Flowers, are occafioned by the Separa- but not any way only difcover affect their Pro- duétion. 8. Plato thought Colour to be a kind of Flame, confifting of moft minute Particles, very congruous to the Pores of the Eye, and darted againit it from the Object. g. Some Moderns will have Colour to be a kind of Internal Light, ofthe more lucid Parts of the Objeét darken’d, and confequently al- ter’d by the various Mixtures ofthe lefs lumi- nous Parts, o. Others, as did fome ofthe ancient Atomifts, maintain Colour not to be a lucid Stream, but a corporeal Effuvium iffuing out of the coloured Body. 11. Others account for all Colours out of the various Mixture of Light and Darknefs : Andthe Chymitfts will have it fometimes arife from the Sulphur, and fometimes from the Salt, that isin Bodies; and fome alfo from the third Hypoftatick Principle, i. e. Mercury. 12. The moft popular Opinion, is that of the Followers of Arijtotle, who maintain, that Colour is a Property inherent in the coloured Body, and that it exifts without any Dependance on Light. 13. The Cartefians, who make the SenfaLight in different Proportions. In order to tion of Light to be the Impulfe made on the underftand this, it may not be improper to Eye by certain folid, but very minute Glofay fomething concerning the Phenomenon of bules, eafily permeating the Pores of the Air Colowrs, as it hath been difcover’d by the late and Diaphonous Bodies: Thefe derive Colour t PhilofophérSir I/fzac Newton. from the various Proportion ofthe direct Provy may be confider’d two ways. grefs or Motion ofthefe Globules, to their Quality refiding in the Body, that is Circumrotation or Motion round their own fo and fo colour’d, or which doth Centres ; by which Means theyare qualify’d the Light after fuch and fuch a man- to ftrike the Optick Nerve, after diftinét and : Or, (25) As moreproperly the Light divers Manners, and fo do produce the Pert felf, which b ing fo modify’d, fhines upon ception of various Colours. : f € Organ of Sight, and produces that Senfa14. They own, that as the coloured Bodyis Co ur. not immediately apply’d to the Organ, to o dour is defin’d to be nhe- cafion the Senfation, and as no Body can affeét ight, whereby, ac g dif- the Senfe but by immediate Conta t, the or Magnitudes of ; d Body does not excite the Senfgtion of itfelf, or contribute any th to it, othetwife than by moving fome intery ios’d Medium, and tion of the nutritive Juice of Plants, or from the Alteration of their Parts, whereby the fmaller Corpufcles, which are carry’d to the Surface of the Flower-leaves, are of different Forms, and do thereby reflect the Rays of by that the O aan ol 15. They add, That as it is found that Bodies do not affeét the Senfe in the Dark, and that Light only occafions the Senfation of Colour, by g the Orgar and that coloured Boc 8G i |
