Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/634

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hdrbatum, feems owing to the leaves being fo covered with a woolly down that they look bearded. And when this word is written barbajfum, it may probably be given as the name of fome of thofe fpecies of mullein, which are not hairy, as our black or fage-leaved mullein, and be a corruption of the word verbafcum. This black mullein has no lefs title than the white or bearded kind, to the name T'hapfum. Its flowers being of a yet finer yellow than thofe uf that kind, and being as fit for the ufc of feining. The glovers of Hertford fiii re ufmg this fpecies for their leather gloves.

THARGELIA, e*eyu*i*, in antiquity, an Athenian feftival, in honour of the fun, and his attendants the hours ; or, as o- thers think, of the Oelian Apollo and Diana. For an account of the ceremonies of this folemnity, fee Potter, Archieol. Gnec. 1. 2. c. 20. T. i. p. 400. feq.

THARGELION, 0*(iyD*i«» s in chronology, the eleventh month of the Athenian year. It contained thirty days, and anfwered to the latter part of our April, and the beginning of May. See the article Month.

It took its name from the fe&mlTbargelia, kept in it. Sec the article Thargelia, fupra.

THAS1UM Marmor, in the writings of the antients, a name given to a fpecies of marble, uled in building. It had its name from the ifland Thafus, one of the Cyclades, where it was dug ; it was of a dufky greyifh white, and feemed to be compofed of the fame matter with the common white marbles with grcyifh veins ; only that the matter of the veins here did not run into thofe determinate parcels, but were blended among the whole mafs.

THAUGHTS, or Thoughts, in a boat, are the benches on which the rowers fit to row.

THEATRIC Bandages, a term ufed by Hippocrates, to exprefs the parade of furgery in applying bandages fur fhew, when there was no real ufe in them. All fuch bandages he called Theatric, proper only to be looked at.

THEBANUS Ophites, in natural hiftory, a name given by fome of the antients, to that fpecies of the Ophites, or fer- pentine marble, more commonly called Ophites niger, the black ferpentine. See the article Ophites.

THEDO, in ichthyology, a name given by Figulus and others, to the trout. See the article Trutta.

THEIOCRUS, in the materia medica of the antients, a name given by fome to the Melanieria, a mineral fubftance of a vitriolic nature, and of a yellow colour, but turning black on touching common water.

This name Tlieioa'us fignifics only fulphur-coloured, and was at firft ufed with the name of vitriol, as expreffive of the difference of this kind from others ; but in time it became common to ufe it alone.

THELE, a word ufed by fome to exprefs the nipple, and by others for the whole breaft.

THELIGONIUM, in botany, the name of a genus of plants, called by the common authors of botany, cynocrambe. The characters are thefe : The male and female flowers arc pro- duced in the fame plant. In the male flower the cup is com- pofed of one leaf, of a turbinated form, lightly divided into two fegments with the jaggs turning downward. There are no petals. The (lamina are numerous, being ufually twelve at lead ; they ftand erect, and are of the length of the cup ; and the antheras are Tingle. The female flower has an ex- tremely final! one-Icaved cup, which is bifid, and its fegments gape open. There are no petals. The piftil has a globofe germen ; the ftyle is fhort, and the ftigma obtufe. The fruit is a globofe capfule, of a coriaceous texture, having only one cell, and containing only one globofe feed. Litmeci Gen. Plant, p. 406. Toitrn. lnft. p. 485.

THEMIS, in aflronomy, a name given by fome to the third fatellite of Jupiter. Lowth. Abr. Philof. Tranf. Vol. 1. p. 408.

THENAR, (Cycl.) a very thick and flefhy mufcle, in fome mea- sure pyriform, lying on the firft phalanx of the thumb to- ward the palm of the hand, the large eminence in which is chiefly formed by it. It is fixed to the bone which fupports the thumb, and to the neighbouring part of the great internal annular or tranfverfe ligament of the carpus. It is in fome meafure bicipital ; two diftinct portions anfwering to the two infertions. As it runs along the firft phalanx, thefe two por- tions unite, and diminishing in thicknefs, arc both inferted by one tendon in the lateral internal part of the head of the firft phalanx, in the lateral part of the bafis of the fecond, and in the lateral ligament of that joint. The void fpace be- tween the two portions of this mufcle gives pafTage to the tendon of the flexor polUcis longtts. That portion which lies neareft the hollow of the hand is largeft ; and its tendinous extremity is inferted in the firft fefamoide bone, fituated at the bafis of the fecond phalanx. IFinflow's Anat. p. 196.

Thenar Pedis, a mufcle made up of fevcral portions, and lying on the inner edge of the fole of the foot. It is fixed by three or four flefhy fafciculi to the lower and inner part of the oscalcis, feaphoides, and cruciforme majus, and a little in the annular ligament under the inner ankle, which belongs to the tendon of the flexor longus. From all thefe infertions the fafciculi approach each other, as they advance under the firft bone of the metatarfus, and are fixed in the internal fefa- 4

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moide bone, and infide of the firft phalanx near its bafe ; and there is another fafciculus fixed by one end of the os feaphoides, and cuneiforme majus ; and by the ot her to the external fefamoide bone, and outfide of the firft phalanx of the great toe. ^inflow's Anat. p. 222.

THENSA, among the Romans, a veil or canopy, ufed in the chariots at games ; and likewife to cover a feat of ftate. Piiifc. in voc.

Tbenfa could not be granted to any but by the exprefs al- lowance of the fenate. Hift. Acad. Infcript. Vol. 1. n. 359.

THEOBROMA, in botany, the name of a genus of vegetables, including the cacao and the guazuma of Marnier. The cha- racters are thefe : The cup is a three-leaved perianthium re- flex and open, and is compofed of oval, concave, and deci- duous leaves. The corolla is compofed of five petals, erect, open, concavely galeated, and terminated by a bifid brittle. I 'fie nectarium is campanulated, and conlifts of five pe- tals; it is fmaller than the flower, and conlifts of five con- nected parts. The ftamina are five-pointed filaments of the length of the nectarium ; each has its top divided into five fegments, and carrying five apices or anthers;. The germen ot the piitil is oval, the ftyle is pointed, and is of the length of the nectarium, and the ftigma is fimple. The fruit is a woody fubftance, ribbed in five places on the furface, and di- vided into five lodgments of feeds within. The feeds are numerous, flefhy, and of an oval figure. There is fome dif- ference in the fruit of the feveral fpecies of thefe trees ; the cacao having a long fruit, tapering at each end, and the gua- zuma a globular one, full of tubercles, and perforated in the manner of a fieve, but divided into five lodgments within. Untusi Gen. Plant, p. 367. Plum'ur, Gen. 18. Tourn. lnft. p. 444.

THEODOLITE {Cycl.) — This inftrument is now commonly made ufe of by lurveyors. One of the belt of the kind feems to be Mr. Siffon's lateft improved Theodolite ; a description of which may be found in Mr. Gardner's Practical Surveying improved ; from whence it has been inferted in a late treadle of practical geometry, publifhed at Edinburgh 1745, in 8°. unuer the care, as it is commonly thought, of the Jate cele- brated Mr. M'Laurin.

In this inftrument the three ftaves, by brafs ferrils at top, fcrew into bell metal joints, moveable between brafs pillars, fixed in a ftrong brafs plate ; in which, round "the center is fixed a focket with a ball moveable in it, and upon which the four fcrews prefs that fet the limb horizontal. Next above is fuch another plate, through which the faid fcrews pafs, and on which round the center is fixed a fruftum of a cone of bell- metal, whofe axis, being connected with the center of the ball, is always perpendicular to the limb, by means of a coni- cal brafs ferril fitted to it, whereon is fixed the compafs-box, and on it the limb, which is a ftrong bell-metal ring, whereon are moveable three brafs indexes, in whofe plate are fixed four brafs pillars, that joining at top, hold the center-pin of the bell-metal double fextant, whofe double index is fixed in the center of the fame plate. Within the double fextant is fixed the (pint level, and over it the telefcope. The compafs-box is graved with two diamonds for north and fouth, and with 20 degrees on both fides of each, that the needle may be fet to the variation, and its error alio known. The limb has two flower-de-luces againft the diamonds in the box, and is curioufiy divided into whole degrees, and num- bered to the left hand at every 10° to twice 1 «o°, having three indexes (with Nonius's divifions on each for the decimals of a degree) that are moved by a pinion fixed below one of them without moving the limb, and in another is a fcrew and fpring under, to fix it to any part of the limb : It has al- fo divifions numbered for taking the quarter girt in round tim- ber; to which a fhorter index is ufed, having Nonius's divi- fions for the decimals of an inch; but an abatement muft be made for the bark, if not taken off.

The double fextant is divided on one fide from under its cen- ter (when the fpirit-tube and telefcope are level) to above 60 degrees each way, and numbered at 10, 20, &c. And the double index (through which it is moveable) {hews on the fame fide the degree and decimal of any altitude or deprefiion to that extent, by Nonius's divifions; on the other fide are divifions numbered for taking the upright height of timber, csV. in feet, when diftant ten feet, which at 20 muft be doubled, and at 30 trebled; and alfo the quantities for re- ducing hypothenufal lines to horizontal : It is moveable by a pinion fixed in the double index. See the article Sur ve yikg. The telefcope is a little fhorter than the diameter of the liiub, that a fall may not hurt it ; yet it will magnify as much, and fhew a diUinct object as perfect, as moft of treble its length ; in its focus are very fine crofs wires, whofe interfection is in the plane of the double fextant, and this was a whole circle, and turned in a lathe to a true plane, and is fixed at right angles to the limb ; fo that whenever the limb is fet horizon- tal (which is readily done by making the fpirit-tube level over two fcrews, and the like over the other two) the double fex- tant and telefcope are moveable in a vertical plane, and then every angle taken on the limb (though the telefcope be ne- ver fo much elevated or deprefled) will be an angle in the plane of the horizon, and this is absolutely neceifary in plot- ting