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we have called an ellipsis, will manifestly rately by Duhamel and others, as pracvary according to the law of the alternate tised in the south of France. The fir is motion in the mandrel. When the man- generally allowed to remain untouched drel moves uniformly forward, the cut till it is thirty or forty years old. When will be the common helix or screw; and it is to be worked, which is early in the the motion is used to make screws, spring, a small hole is first made in the though not very frequently, because good ground at the foot of the tree, the earth turners can easily make them by a notch of which is well rammed, and serves as a ed cutting tool, called the screw.

receptacle for the juice. The coarse The act of turning is so extensively ap- bark' is then stripped off from the tree, a plicable, that it would require a volume little above the hole, down to the smooth to describe its uses, and the methods of inner bark, after which a portion of the practising it. Every round thing which inner bark, together with a little of the is made by human bands may be referred wood, is cut out with a very sharp tool, to this art, as one of its products. The so that there may be a wound in the tree largest columns, the most ponderous ar about three inches square, and an inch tillery, and the minutest pivots of watch- deep. Immediately afterwards the tur. work, with all wheel-work, rotatory ma. pentine begins to exude in very transpachines, vessels, &c. are worked in this rent drops, which escape chiefly from the method.

wood immediately under the inner bark. TURNSOLE. See LITMUS.

The hotter the weather is, the greater is TURPENTINE. See RESINS.

the supply of resin; and to facilitate the Turpentine, of which there are various supply, the incisions are enlarged every kinds, are all products of some of the three or four days, by cutting off thin species of the pinus. From this genus are slices, till at the end of the year it is about obtained not only turpentine, but rosin, a foot and a half wide, and two or three pitch, tar, &c. which are employed so ex- inches deep. The whole time during tensively in ship-building, and in the rig which the turpentine flows is from the ging also : likewise in varnishes.

end of February to October. In the win. There are three varieties of pine tur. ter it entirely ceases, but in the ensuing pentine, commonly known under that spring a fresh incision is begun a little name in Europe : namely, 1. The com. above the former, and managed in the mon turpentine, obtained chiefly from the same manner. This practice is continued pinus sylvestris (Scotch fir). 2. The annually for about twelve or fifteen years Strasburgh turpentine, yielded by the pi. in some parts, and in others a shorter nus picca (silver fir). And, 3. The Ve- time, on the same side of the tree, till the nice turpentine, procured from the pinus later incisions are so high as to be out of larix (larch). Of the three first mention. reach without the assistance of steps; af. ed turpentines, the Venice is the thinnest ter which the contrary side of the tree is and most aromatic ; the Strasburgh the begun upon, and worked in a similar mannext in these qualities; and the common ner for as many years, during which is the firmest and coarsest. The two time the first incisions are grown up, and former are often adulterated by a mixture are fit to be cut afresh. In this way, a of the common turpentine and oil of tur- healthy tree, in a favourable soil, may be pentine; and it is to be observed, that the made to yield from six to twelve, or more, terms Venice and Strasburgh turpentine pounds of turpentine annually, sometimes are not now appropriate, as they are pro. for a century; and even the timber is not cured from various countries.

soon injured by this constant drain. The Common turpentine is obtained largely flow of turpentine discontinues altogether in the pine forests in the south of France, about October, and the liquid resin colin Switzerland, in the countries on the lected during the year, from each tree, is north of the Pyrenees, in Germany, and put together for further purification. But in many of the southern states of North a considerable quantity of the resin has America. The greater part of what is concreted during that time around the inconsumed in this country is imported cision, particularly as the heat declines; from North America. The method of and in the winter, when it has hardened obtaining it is by making a series of in- considerably, it is scraped off, and forms cisions through the bark of the tree, from what is technically called barras, or in which the turpentine exudes, and falls some provinces galipot, which differs down into holes, or other receptacles at from the more liquid turpentine in conthe foot.

sistence, and probably contains a less pro. The process is described very accu portion of essential oil. The galipot is

much used in making flambeaux, whien Turquoise is generally considered as mixed with suet; but the greater part of fossil-bone, or ivory penetrated by oxide it, as well as the liquid turpentine, is sub- of copper; it appears, however, from the jected to further processes.

above analysis, that the colouring matter The Strasburgh turpentine, the produce is phosphate of iron. The oriental tur. of the silver fir, is the most fragrant of all quoises are found near Meched in Persia, the pine turpentines, and only inferior to also in Mount Caucasus, in Egypt and the true Chio; but it is not often seen in Arabia. The occidental ones are found the shops. It is obtained by rude incision in Languedoc in France, and in Hungary. of the bark by the peasants in the vast Turquoise was formerly in some estima. pine forests on the western Alps. The tion for rings and other articles of per. first cut is made as high as the hatchet sonal ornament; but its value has greatly will reach, and these are renewed annual. declined in modern times. The colour ly from above downwards to within a foot turquoise changes gradually by exposure of the ground. But the finest kind of tur to the air, from blue to green : when it pentine yielded by this tree is that which arrives at this state, its commercial value exudes from soft tubercles, or swellings is wholly extinct. of the inner bark. The peasants carry TURRITIS, in botaný, tower-mustard, a with them a large cow's horn, with the genus of the Tetradynamia Siliquosa point of which they pierce these tuber. class and order. Natural order of Silicles, and collect the juice in its hollow. quosæ, Cruciformes, or Cruciferæ. Essen

The true Venice turpentine, or resin of tial character: silique very long, angular; the larch, is obtained from the Tyrol and calyx converging, erect; corolla erect. Savoy, and also from Dauphiny, by boring There are eight species. holes about an inch in diameter, with a TURRÆA, in botany, a genus of the gentle descent, in the most knotty parts Decandria Monogynia class and order. of the tree. To these are adapted long Natural order of Trihilata. Meliæ, Jus. perforated pegs, which serve as gutters sieu. Essential character: calyx fire. to convey the juice into troughs placed toothed; petals five; nectary toothed, beneath. It is yielded during the whole cylindrical, bearing the anthers at the of the summer, and is simply purified by mouth between the teeth; capsule penstraining through hair sieves. A full tacoccous; seeds two. There are five grown larch will sometimes yield seven species. or eight pounds of turpentine annually . TUSCAN order, in architecture, the for forty or fifty years.

first, simplest, and most massive of the TURQUOISE. The colour of this sub- five orders. stance is pale sky-blue, passing into indi. TUSSILAGO, in botany, colt's-foot, a go-blue, and pale apple-green. It occurs genus of the Syngenesia Polygamia Su. in mass, or disseminated. Its fracture is perflua class and order. Natural order even. Its hardness is nearly equal to of Compositæ Discoidea Corymbiferæ, that of glass; it is difficultly frangible. Jussieu. Essential character: calyx scales Specific gravity 3.12. Before the blow. equal, as long as the disk, somewhat pipe its colour changes to greyish-white, membranaceous; down simple ; recepta.' and it becomes friable, but it does not cle naked. There are fourteen species. melt. It is soluble in nitro-muriatic acid, TWILIGHT, that light, whether in the and the European varieties are so in nitric morning before sunrise, or in the evenacid; this menstruum, however, has no ing after sunset, supposed to begin and action on the Persian turquoises. It is end when the least stars that can be seen composed, according to Buillon la Grange, by the naked eye cease, or begin to ap

pear. By means of the atmosphere it

happens, that though none of the sun's Phosphate of lime ... 80

direct rays can come to us after it is set, Carbonate of lime ...

yet we still enjoy its reflected light for Phosphate of iron, with a 2

some time, and night approaches by de. trace of manganese

grees; for after the sun is hidden from Phosphate of magnesia :.

our eyes, the upper part of our atmo. Alumina . . . . . . .

sphere remains for some time exposed to Water . . . . . . . .

its rays, and from thence the whole is il. Loss . . . . . . . . 1

luminated by reflection. But as the sun

grows lower and lower, that portion of 100

the atmosphere which is above our hori. zon becomes enlightened till the sun bas

of

Latitude.

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got eighteen degrees below it; after timual night; and w 11, that the twilight which it ceases to be illuminated thereby, lasts the whole night: till it has got within as many degrees of the eastern side of the horizon; at which time it begins to illuminate the atmosphere again, and in appearance to dif solli * SOCE O fuse its light throughout the beavens, which continues to increase till the sun

13269 be up. Hence it is, that during that part of the year in which the sun is never eighteen degrees below our horizon, there is a continued twilight from sun. setting to sun-rising. Now that part of the year in the latitude of London is, while the sun is passing from about the fifth degree of Gemini to the twelfth of Cancer; that is, from the middle of May to the middle of July.

As the twilight depends on the quantity of matter in the atmosphere fit to reflect the sun's rays, and also on the height of it, (for the higher the atmosphere is,

NE the longer will it be before the upper parts of it will cease to be illuminated,) the duration of it will be various. For

NE instance, in winter, when the air is condensed with cold, and the atmosphere upon that account lower, the twilight will allowa be shorter; and in summer, when the limits of the atmosphere are extended by the rarefaction and dilatation of the air of

Ownnweg which it consists, the duration of the twilight will be greater. And for the like

ស ១ ១ reason, the morning twilight, the air being at that time condensed and contracted by the cold of the preceding night,

ONUNC will be shorter than the evening one, when the air is more dilated and ex. panded.

A Conto The beginning and end of twilight has been variously stated, by different observers; but, in our latitude, it may be

00AE OF said to begin and end when the sun is about eighteen degrees below the hori. zon : hence, when refraction is allowed for, the atmosphere must be capable of reflecting sensible light at the height of about forty miles. The duration of twi. light is greater or less as the sun moves more or less obliquely with respect to the horizon: hence it is shortest near the time of the equinoxes, because the equi. noxial intersects the horizon less oblique. ly than any lesser circle parallel to it. Dr. Long has calculated the duration of twilight in different latitudes, and for the several different declinations of the sun: TYCHONIC system, or hypothesis, an orthe result he laid before the public in the der or arrangement of the heavenly bo. following table, where the letters c d sig. dies, of an intermediate nature between nify that it is then continual day; on con. the Copernican and Ptolemaic, or parti

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cipating alike of them both. This system lours, than the ancient ones. But both had its name and original from 'sycho kinds seem to be made of the same whit. Brahe, a nobleman of Denmark, who liv. ish clay as our white glazed earthen ware; ed in the latter part of the last century. the modern ones are commonly painted This philosopher, though he approved with birds, flowers, &c. The ancient of the Copernican system, yet could not ones are only five inches and a quarter reconcile himself to the motion of the square, and about three-quarters of an earth, and being, on the other hand, inch thick ; the modern ones six inches convinced the Ptolemaic scheme could and a half square, and three-quarters of not be true, he contrived one different an inch thick from either. In this the earth has no mo. TYMPAN, or TYMPANUM, in architection allowed it, but the annual and diur. ture, the area of a pediment, being that nal phenomena are solved by the motion part which is on a level with the naked of the sun about the earth, as in the Pto. of the frieze. Or it is the space included lemaic scheme ; and those of Mercury between the three cornishes of a trianguand Venus are solved by this contrivance, lar pediment, or the two cornishes of a though not in the same manner, nor so circular one. Sometimes the tympan is simply and naturally, as in the Copernican cut out, and the part filled with an iron system. The Tychonic system then sup- lattice, to give light, and sometimes it is posed the earth in the centre of the enriched with sculpture in basso relievo. world, that is, of the firmament of stars, Tympan, among printers, a double and also of the orbits of the sun and frame belonging to the press, covered moon; but at the same time it made the with parchment, on which the blank sun the centre of the planetary motions, sheets are laid in order to be printed off. viz. of the orbits of Mercury, Venus, See Printing Mars, Jupiter and Saturn. Thus the sun, TYMPANUM, or TIMpan, in mecha. with all its planets, was made to revolve nics, a kind of wheel placed round an about the earth once a year, to solve the axis, or cylindrical beam, on the top of phenomena arising from the annual mo which are two levers or fixed staves, for tion; and every twenty.four hours to ac- the more easy turning the axis, in order count for those of tire diurnal motion. to raise a weight required. The tympaTYGER. See FELIS.

num is much the same with the peritro. TYLE, or Tile, in building, a sort of chium, but that the cylinder of the axis thin, fictitious, laminated brick, used on of the peritrochium is much shorter and the roofs of houses; or more properly, a less than the cylinder of the tympanum. kind of fat clayey earth, kneaded and TYMPANUM of a machine, is also used for moulded, of a just thickness, dried and a hollow wheel, wherein one or more burnt in a kiln like a brick, and used in people, or other animals, walk, to turn the covering and paving of houses. See it; such as that of some cranes, calenBRICK.

ders, &c. There are various kinds of tyles, for TYPE, a copy, image, or resemblance the various occasions of building; as of some model. This word is much used plain, thack, ridge, roof, crease, gutter, among divines, to signify a symbol, sign, pan, crooked, Flemish, corner, hip, dor. or figure of something to come ; in which mar, scallop, astragal, traverse, paving, sense it is commonly used with relation to and Dutch tyles.

antitype, which is the thing itself, whereFlemish or Dutch tyles are of two kinds, of the other is a type or figure. ancient and modern. The ancient were TYPHA, in botany, a genus of the Moused for chimney foot-paces; they were noecia Triandria class and order. Natural painted with antique figures, and fre. order of Calamariæ. Typhæ, Jussieu. Esquently with postures of soldiers; some sential character: male, ament cylindri. with compartments, and sometimes with cal; calyx indistinct, three-leaved; co. moresque devices : but they come much rolla none; female, ament cylindrical, short of the design and colours of the below the males; calyx a villose hair; modern ones. The modern Flemish corolla none; seed one, placed on a ca. tyles are commonly used plastered up in pillary down. There are two species, ris the jambs of chimneys, instead of chim. T. latifolia, great cat's tail, or reed mace ; ney-corner stones. These are better and T. angustifolia, narrow-leaved cat's glazed, and such as are painted (for tail. some are only white) are done with TYPOGRAPHY, the art of printing. more curious figures, and more lively co. See PRINTING and STEREOTYPE.

U Or u, the twentieth letter, and fifth by the more quick descent of light bodies

, vowel of our alphabet, is formed in a receiver when exhausted of its air, in the voice by a round configuration of there must be some vacuities between the lips, and a greater extrusion of the the parts of the remaining air ; wbich is under one than in forming the letter o, sufficient to constitute a vacuum. Indeed, and the tongue is also more cannulated. to this it may be objected by a Cartesian, The sound is short in crust, must, tun, that those vacuities are filled with matelub: but is lengthened by a final e, as in ria subtilis, that passes freely through the tune, tube, &c. In some words it is rather sides of the vessel, and gives no resistacute than long; as in brute, flute, lute, &c. ance to the falling bodies: but as the exIt is mostly long in polysyllables; as in istence of this materia subtilis can never anion, curious, &c. but in some words it be proved, we are not obliged to allow is obscure, as in nature, venture, &c. the objection, especially since Sir Isaac This Ictter, in the form, V, or v, is pro. Newton has found that all matter affords perly a consonant, and as such is placed a resistance nearly in proportion to its before all the vowels; as in vacant, veral, density. There are many other arguments ribrate, &c. Though the letter v and u to prove this, particularly the motions of had always two sounds, they had only the the comets through the heavenly regions, form v, till the beginning of the fourth without any sensible resistance, the difcentury, when the other form was intro. ferent weight of bodies of the same bulk, duced, the inconvenience of expressing &c. All the parts of spaces, says Sir two different sounds by the same letter Isaac Newton, are not equally full; for if having been observed long before. In they were, the specific gravity of the fiuid numerals V stands for five, and with a which would 6ll the region of the air, dash added at top, thus, V, it signifies

could not, by reason of the exceeding 5000.

great density of its matter, give way to VACCINATION. See SURGERY.

the specific gravity of quicksilver, gold, VACCINIUM, in botany, bilberry, or

or any body, how dense soever; whence whortleberry, a genuis of the Octandria Mo.

neither gold, nor any other body, could nogynia class and order. Natural order

descend in the air ; for no body can deof Bicornes. Ericæ, Jussieu. Essential

scend in a fluid, unless it be specifically character: calyx superior; corolla one

heavier than it. But if a quantity of mat. petalled; filaments inserted into the re

ter may, by rarefaction, be diminished in ceptacle; berry four-celled, many-seed.

a given space, why may it not diminish in ed. There are twenty-seven species.

infinitum ? And if all the solid particles VACUUM, in philosophy, denotes a

of bodies are of the same density, and space empty, or devoid, of all matter or

cannot be rarefied, without leaving pores, body. It has been the opinion of some

thiere must be a vacuum. philosophers, particularly the Cartesians,

VADE mecum, or Veni mecum, a Latin that nature admits not a vacuum, but that phrase, used in English to express & the universe is entirely full of matter: in thing that is very handy and familiar, and consequence of which opinion they were which one usually carries about with them; obliged to assert, that if every thing con

chiefly applied to some favourite book. tained in a vessel could be taken out or VAGINA, properly signifies a sheath annihilated, the sides of the vessel, how or scabbard : and the term vagina is used, ever strong, would come together; but in architecture, for the part of a terininus, this is contrary to experience, for the because resembling a sheath, out of which greatest part of the air may be drawn out the statue seems to issue. of a vessel by means of the air-pump, not. VAGINALIS, tie sheath-bill, in natural withstanding which it will remain whole, history, a genus of birds of the order if its sides are strong enough to support Grallæ. Generic character : bill strong, the weight of the incumbent atmosphere. thick, compressed; upper mandible co. Should it be objected here, that it is im vered above with a moveable horny possible to extract all the air out of a ves sheath; nostrils placed before the sheath; sel, and that there will not be a vacuum face naked and papillous; wings with on that account; the answer is, that since an obtuse excrescence under the flex. a very great part of the air that was in ure; claws grooved. V. alba, or the the vessel may be drawn out, as appears white sheath-bill, the only species known,

VOL. XII.

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