TAL
Tail, in tile manege. Many affirm that the dock of a horfe*8 Tail ferves to point out his fixth or fevcnth year ; faying, that about the time that the black fpeck, or eye of the bean begins to difappear, and the cavity to be filled, the dock of the tail becomes longer, by reafon that the vigour of the young years begins to abate; and nature has not ftrength enough to nourifh and keep up the joints or knots that form the duck ; fo that when the horfe is lix years old, one of thefe joints flackens, and begins to fall down ; and a year after, an- other defcends in like manner. But this relaxation or down- falling happens fooner in fome than in others, according as they have been well or ill kept, with reference to feeding, houfing, and working. Accordingly we find the marks of a horfe's age, taken from his Tail, are fo erroneous, that we fee a great many jockics maintain, that the firft joint defcends when he is nine, and the fecond when he is ten years old.
Tails of Comets. We have an enquiry into the caufe of the Tails of comets by Mr. Euler in the Mem. de 1'Acad de Ber- lin, Tom. 2. p. 117. feq. He thinks there is a great Affi- nity between thefe Tails, the zodiacal light, and the aurora borealis ; and that the common caufe of them all is the action of the fun's light, on the atmofpheres of the comets, of the fun, and of the earth. He fuppofes that the impulfe of the rays of light on the atmofphere of comets, may drive fome of the finer particles of that atmofphere far beyond its limits ; and that this force of impulfe combined with that of gravity to- wards the comet, would produce a Tail, which would always be in oppofition to the fun, if the comet did not move. But the motion of the comet in its orbit, and about an axis, muff. vary the petition and figure of the Tail, giving it a curvature, and deviation from a line drawn from the center of the fun to that of the comet ; and that this deviation will be greater, as the orbit of the comet has the greater curvature, and that the motion of the comet is more rapid. It may even happen, that the velocity of the comet, in its perihelion, may be fo great, that the force of the fun's rays may produce a new Tail, before the old one can follow ; in which cafe the comet might have two or more Tails. The poffibility of this is con- firmed by the comet of 1744, which was obferved to have feveral Tails while it was in its perihelion. See the article Zodiacal Light, and Aurora Borealis.
TAIPARA, in zoology, the name of a Brafilian fpecies of pe- roquette. It is of the fize of a lark, and of a pale green colour over its whole body ; its tail is fhort, not reaching beyond the tips of the wings when clofed. Its beak is red, and its legs are grey. Near the origin of the beak it has a iemilunar red fpot on the head, and a yellow fpot in the middle of each wing. It builds in the deferted abodes of ants on trees. Marggrave's Hift. Braf.
TA1NHA, in zoology, a name given by fome to a fpecies of mullet caught in the American feas, and more ufually called the curema, Willughby, Hift. Pifc. p. 277. See the article Curema.
TAL, a name ufed by fome writers on the materia medica to exprefs the dung of peacocks ; and by fome of the chemical writers, for any alkali fait.
TALA, in botany, a name by which fome authors call the plant whofe feed is the fefamum or oily purging grain of the fhops. Herm. Muf. Zeyl. p. 58.
TALABONG, in natural hiftory, a name given by the inhabi- tants of the Philippine Iflands to a fpecies of heron, common among them ; which is much fmaller than our heron, and perfectly white all over.
TAL/EDITES, T*fc*t&Tu?, in antiquity, gymnical exercifes in honour of Jupiter ra^aioj. Potter^ Archseol. Grsec. 1. 2. c. 20. T. 1. p. 432.
TALARIUS Ludus, among the Romans, a game fomewhat re- fembling our dice-playing, and performed with a kind of gold or ivory dice, which they fhook as we do in a box, before they threw them. There was this difference, however, be- tween their game and ours, that our dice have fix fides, be- caufe they are cubical ; but theirs had but four, and were co- nically tnaped. They made ufe of them for divination, as well as playing ; and they concluded upon a good or evil au- gury, according to what came up. As they ufually threw four of them at a time, the beft chance was when four dif- ferent fides came up. The fides were called by the name of fome animal, as the dog, vulture, bafilifk, &c. Or of fome deity, as Venus, Hercules, &c. Some authors have been of opinion, that they were marked with the forms of animals, or images of Gods, and not with numbers or dots, as our dice are. Danet. in voc.
TALASSIO, among the Romans, an acclamation ufed at mar- riages ; for the origin of which fee Piti/c. and Danet in voc. and Livy 1. 9.
TALC, (Cycl.) in natural hi ftory, the name of a large clafs of foffile bodies. See Tab. of Foffifs, Claff. 1. The Talcs in general are defined to be foffils, compofed of broad, flat, and fmooth laminae or plates, laid evenly and re- gularly on one another ; eafily fiffile, according to the fite of thefe plates, but not all io in any other direction ; flexile and elaftic; bright, Alining, and tranfnarent ; not giving fire with ileel, nor fermenting with acid mcnltrua, and fuftaining the force of a violent fire without calcining.
TAL
By thefe characters, the Talcs may be diflinguifhed from all other bodies which refemble them ; and, according to their feveral natural and eflential differences among one another, they arc themfelvcs divided into two feparate orders, and un- der thofe into four genera.
The Talcs of the firft order are thofe compofed of plates of great extent, each making fingly the whole horizontal furface of the rnafs.
Thofe of the fecond order are thofe compofed of fmall plates ? in form of fpangles, irregularly difpofed, and ufually many of them concurring in different directions, to the formation of one of the furfaces of the maft. Hill's Hift. of FofT. p. 71. The genera of the firft order are two : The firft is of tfiofe compofed of vifibly feparate plates of extreme thinnefs, and each Affile again into a number of others yet finer. The Talcs of this genus are czMedfpeculares.
The fecond genus is of thofe which are compofed of feparate plates of conliderable thicknefs, and thofe not fiffile into any thinner. The Talcs of this genus are called hyaline:. The genera of the fecond order are alfo two. The firft is of thofe compofed of fmall plates, in form of fpangles, each fif- file into many yet finer and thinner ones. The Talcs of this genus are called bratlearia.
The fecond genus is of thofe compofed of fmall plates in form of fpangles, which are moderately thick, and are either not fiffile at all, or are only fo to a certain degree, or into a fmall number of others yet thick ones, and thofe no farther Affile* The Talcs of this laft genus are called elafinides. Authors have hitherto been ufed to call alio another fet of bo- dies by the name of Talcs, with the addition of the adjective fibrofe ; but as thefe are found not at all of the nature of the true Talcs, they are now diflinguifhed by the name jibrarite. See the article Fibrarije.
Authors arc divided as to the origin of the word Talc. Lemery derives it from the High-Dutch Talcb, tallow, becaufe it feels greafy. But this is improbable ; fince Avifenna, who had no commerce with the Germans, ufes the word, and tell us, that the after of Lemnos is Tallz, which cannot be calcined but with the moft intenfe fire, and which is dangerous when taken inwardly. Its origin therefore, according to Mr. Pott 9 feems rather Arabic. Casfalpinus tells us, that Talc, among the Moors, fignifies Jlar, and that they underftand thereby the JleUa famia. Johnfon alfo fays the word is Arabic, figni- fying fmall mining ftars. This term does not occur among the antients, as Theophraftus, Diofcorides, or Pliny ; tho* fome critics pretend that Diofcorides defigned it byjlella terra, Ceefalpinus and Salmafius endeavour to prove that Talc is the apbrofelene or feleniies of Diofcorides. Thofe authors alfo pretend that Pliny meant the fame thing by febijius. Casfal- pinus refers Talc to the galeucos argyrodamanti ftmilis ; and Bcetius to the argyrodamas itfelf. Some think that a pafiage in Pliny, Lib. xxxvi. c. 22. may be underftood of Talc. Avifenna call it lapis tuna ; and Albertus Magnus, apbrofe- lene. The moft common fpecies in Germany is called katzen- jiluer, or katzen- glimmer . It is alfo named from a particular place where it is found, Kipbaufcr-glant%. When it is of a yellow colour, they call it katzen-gold, and in Latin, mua 9 and cbtsrik nit'ulum. In fome places it is alio called J per -glafs. Pott, in Mem. de 1'Acad. de Berlin.
Talc is often confounded with fimilar concretions, as with the fchifi as or lapis fojfilis, with the fpathum ox fpatum, and gyp- fum, Mufcovy-glafs, or glades- -Maria, and the lapis fpecu- laris. Boyle takes it for an alkaline fpathum, and others for other fubftances, from which neverthelefs it differs. Set Pott, in Mem. de 1'Acad. de Berlin, 1746.
The repeated experiments of the chemifts, who expect: great things from an oil of Talc, have abundantly proved that this fubftance is indiffoluble both in acids and alkalies in a liquid, form ; and the moft violent corrolive mineral acids, fuch as fpirit of nitre and aqua-fortis, and the like, make no change in ir. Mr. Du Hammel, in his topiarium hermeticum, indeed fpeaks very largely of a folution of Talc made by means of a long trituration in water alone : This, he fays, in fix hours will reduce Talc into an unctuous or oily fluid. And in the Com- mercium Literarium for the year 1732, there is a paper in which it is affirmed, that Talc may be in part diflblved by the mineral acids, particularly by fpirit of fait; and that the dif- lblved Talc may be afterwards precipitated from the men- ftruum i but, in reality, neither the fuming fpirit of fait, nor the purer acid of fait, dried by a repeated folution and fublimation, with fublimate Mercury, exerts the leaft effect upon this refractory fubftance. It has been alfo faid, in the Memoirs of the Paris Academy, that Talc and oil of vitriol produce alum ; but neither is this found true on experiment ; much lefs is any folution of Talc to be expe&ed from the volatile fpirit of vitriol, the fpirit of naphtha,_or oil of wine, fo much recommended by fome of the chemifts for this purpofe. The greater part of thefe pretences are abfolute frauds, intended only to impofe on credulous perfons, who ex- pect great matters from an oil of Talc ; the others are proba- bly owing to the error of taking other foliated bodies for Talc, fuch as the plated fpars, which eafily fplit into flakes like Talc, and are foluble in any acid.
The burning Talc and fulphur together docs not advance any
thing
