T E T 



iuclics long, veiny, fmootli on both fides ; tapering at the 

 bafe; ferrated with a few (light teeth towards the point. 

 Footjlalh very (hort. Flo'wer-Jlalks fohtary or in pairs, ter- 

 minal, an inch long. Fkrjuers fomewhat raccmoie, one or 

 two on each partial ftalk. Calyx with (ix roundi(h feg- 

 ments. Capfules four, as long as the finger-nail, roundiih, 

 tumid, pointed, very finooth and polifhed. Seedim^A, black, 

 polilhed, covered in its lower half with a whitifli tunic, 

 whofe margin is tootiied. Fahl. 



9. T. ainifolia. Alder-leaved Tetracera. Willd. n. 12. 



<i Leaves oblong, acute, nearly entire ; roughifti beneath. 



Panicle terminal." — Native of Guinea. Branches woody, 

 round, fmooth. Leaves coriaceous, tapering at the bafe, 

 rounded at the extremity, with fomewhat of a point ; moftly 

 entire, but occafionally furnifhed with an obfolete tooth or 

 two near the end ; veiny ; fliining and Imooth above. Calyx 

 with four deep fegmcnts. Petals apparently five. Filaments 

 a httle dilated at the end, with an anther (or lobe) at each 

 fide. Capfuhs four. Seed black, entirely covered by its 

 whitifii tunic. Panicle fimple. Stalls three-flowered. Willd. 



Willdenow fufpefts the AJa indica, of Houttuyn's 

 Dutch edition of the Vegetable Syftem of Linnaeus, v. 4, 

 40. t. 26. f. I, maybe another fpccies of the genus before 

 us. The fame author is alfo inchned to refer Thunberg's 

 Wahlbomia, fee that article hereafter, to Tetracera. 



TETRACHORD, Tetrachordon, formed of Tsrpx, 

 of Tsr'zf 31, four times, and x^P^". " chord, or Jlring, in the 

 Ancient Mufic, was a feries of four founds, of which the ex- 

 tremes, or firfl. and lall, conftituted a fourth. Thefe ex- 

 tremes were fixed and immutable ; the two middle founds 

 were changeable according to the genera, and called 

 mobiles. There were three genera or ways of tuning 

 each tetrachord ; the diatonic, chromatic, and enharmonic. 

 The character of the diatonic was the tone ; of the chro- 

 matic, the femitone ; and of the enharmonic, the quarter- 

 tone. 



A tetrachord in the diatonic y~V 

 genus confifted of one major femi- ^-^ 

 tone and two tones. 



i 





0' 4rw m- 



i 



zzz^^ii^^^S 



In the chromatic genus, of two 

 femitones and a minor third. 



In the enharmonic genus, of a 

 quarter tone, a femitone, and a 

 major third. 



The general fyftem or fcale of the Greeks confifted of 

 tetrachords repeated, as the fcale of Guido does of oftaves. 

 See Greek Mujic. 



The tetrachord of Mercury contained four firings or 

 chords, in the proportion of twelve, nine, eight, and fix ; 

 £0 as to give the fourth, fifth, and oftave of the loweft 

 chord. This is the opinion of Boethius, and after him of 

 Zarhno. Vide Wallis's Append. Ptolem. Harm. p. 178. 



TETRACTIS, in Natural HiJIory, a name given by 

 Linkius, and other authors, to a kind of fiar-fifh, com- 

 pofed only of four rays, the more common kinds having 

 five. 



TETRACTYC Arithmetic. See Arithmetic. 



TETRACTYS, in the Ancient Geometry. The Pytha- 

 goric tetraftys is a point, a line, a furface, and a folid. 



TETRADECARHOMBIS, in Natural HiJIory, the 

 oame of a genus of foffils, of the clafs of the felenitx. 



The word is derived from the Greek Ttrja, four, Jfxjtc^ 

 ten, and pfiffof, a rhomboidal figure, and expreffes a rhom- 

 boidal body confifting of fourteen planes. 



T E T 



The cliarafters of this genus are, that the bodies of it 

 are exaftly of the fame form with the common felenitas ; 

 but that in thefe, each of the end planes is divided into two ; 

 and there are by this means eight of thefe planes, inftead of 

 four. See Selbnites. 



TETRADIAPASON, Quadruple Diapafon, a mufical 

 chord, otherwife called a quadruple eighth, or nine-and- 

 twentieth. See Diapasox. 



TETRADITiE, Tetradites, in Antiquity, a name 

 given to feveral different fefts of heretics, out of lome par- 

 ticular refpeft they bore to the number four, called in 

 Greek Tirpa. Thus the Sabbatians were called tetraditse, 

 from their fading on Eafl;er-day, as on the fourth day, or 

 on Wednefday. 



The Manichees, and others, who admitted of a quater- 

 nity inftead of a Trinity in the Godhead, or four perfons 

 in lieu of three, were alfo called tetraditse. 



The followers of Petrus FuUenfis bore the fame appel- 

 lation of tetraditse, by reafon of the addition they made 

 to the Trifagion, to countenance an error they held, that 

 in our Saviour's pafllon it was not any particular perfon of 

 the Godhead, e. gr. the Son that fuffered, but the whok- 

 Deity. 



The ancients alfo gave the name tetradita; to childi-en 

 born under the fourth moon, and thefe they believed un- 

 happy. 



TETRADIUM, in Botany, from Tfl^aJjov, a party of 

 four, as a file of four foldiers, &c. alluding to the pre- 

 valence of the number four in its parts of fruftification. — . 

 Loureir. Cochinch. 91. — Clafs and order, Tetrandria Tetra- 

 gynia. Nat. Ord. Terebintacee, Juff. ? or perhaps Rutacex. 



Gen, Ch. Cal. Perianth inferior, minute, permanent, 

 of four fpreading acute leaves. Cor. Petals four, ovate, in- 

 curved, or nearly ereft, longer than the calyx. Stam. Fila- 

 ments four, thick, awl-ftiaped, hairy, equal to the corolla in 

 length ; anthers ovate, ereft, of two cells. P//?. Germen 

 roundifti, four-lobed ; ftyle none ; ftigmas four, awl-fiiaped, 

 eredl. Peric. Capfules four, roundifii, burfting at the top. 

 Seeds folitary, roundifh, poliftied, tunicated. 



Eft. Ch. Calyx inferior, of four leaves. Petals four. 

 Capfules four. Seeds folitary, tunicated. 



I. T. trichotomum. Cay ddu dedti of the Cochinchinefe. 

 Native of the hills of Cochinchina. A middle-fized tree, 

 with afcending branches. Leaves pinnate, with an odd one ; 

 leaflets lanceolate, fmooth, entire. Flo-iuers whitifh, in 

 ample, nearly terminal, three-forked dujlers ; or rather, as 

 we prefume, panicles. 



De Theis well remarks, that this genus appears to be 

 allied to Brucea : we think alfo it is evidently very near 

 Fagara (fee thofe articles). In deference to the weighty 

 opinion of Juflieu, we have not, without doubt, referred it 

 to his natural order of Terebintace^ ; but it appears 

 rather to belong to his imperfeftly -defined one of Rutace^, 

 to both which articles we refer the reader. 



Nothing is faid by Loureiro refpefting the qualities or 

 ufes of this tree. 



TETRADRACHM, in Ancient Coinage, a filver coin 

 worth four drachmas, or 3^. fterling, the drachma being 

 valued at gd. But if we eftimate the value of the drachma 

 at a higher rate, that of the tetradrachm will increafe in 

 due proportion. This is the largeft form of Greek filver, 

 coins, excepting the tetradrachm of the Eginean ftandard, 

 which is worth 5^. The largeft tetradrachms weighed from 

 430 to 440 grains. See Drachm and Shekel. 



TETRADYNAMIA, in Botany, (from Tt7^c^,four, and 

 Jyya^ij, power, indicating a fuperiority of four ftamens over 

 the reft,) the fifteenth clafs of the Linnsean artificial fyftemj 



which 



