Page:Cyclopaedia, Chambers - Supplement, Volume 1.djvu/608

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thofc of the flowers, and feparating the flowers one from ano- 1 ther. The feeds are fingle, oblong, and fomewhat cubic in figure, and are crowned with a marginaceous rim. hinnai Gen. Plant, p. 22. The Dipsacus, according toTournefort, is characterized thus: the flower is of the flofculous kind, being compofed of feveral fmall flofcules, colleaed into a kind of a honey- comb-like ftructure ; the head is compofed of feveral imbri- cated leaves, and thefe are fixed to an axis, and laid like fcales over one another. The flofcules arife from the ate of thefe, and are divided into many fegments at their ends ; thefe are placed on the coronated end of an embryo, which after- wards becomes a ftriated feed.

The fpecies of Dipfacus enumerated by Mr. Tournefort are thefe. i. The cultivated great Dipfacm, 2. The great wild Dipfacus. 3. The jagged leaved Dipfacus. 4. The four leaved giant Dipfacus ', with fmooth fcabious like leaves, and a pear fafhioned head : and 5. The Indian great Dipfacus, with numerous heads. Toum. Inft. p. 466.

The leaves of the common wild Tcafell dried, and given in powder, or infufion, are a very powerful remedy againft flatus's and crudities of the ftomach. There is alfo another, though fomewhat whimfical ufe, for which this plant is become fa- mous among the country people. If the heads arc opened longitudinally about September or October, there is generally found a fmall worm in them: one of thefe only is found in each head, whence naturalifts have named it the vermis foli- tarias dipfaci. They collect three, five, or feven of thefe, al- ways observing to make it an odd number, and fealing them up in a quill, give them to be worn as an amulet for the cure of agues. Faith has wrought fo many cures for them, that they are in many parts of the kingdom of much higher repu- tation than the bark. Dipsacus, in medicine, according to fome, is the fame with a Diabetes. Caji. Lex. Med. in voc. Diabetes. See Diabetes. DIPSAS, a fort of ferpent, the biting whereof produces fuch a thirft as proves mortal ; whence it is called Dipfas, which in Greek fignifies thirfty. In Latin it is called fitula, a pail. Mofes fpeaks of it in Deut. viii. 15.

The Hebrew word tzimaon anfwers very well to the Greek Dipfasy and exprefles the thirft occafioned by the biting of this ferpent. Some by the Hebrew tzimaon underftand a de- fart or dry place. Calmet, Diction. Bibl. DIPYRENON, in furgery, the name of a probe, with a double button at the end, refembling two fmall berries growing to- gether. DIRECTION [Cycl)— Quantity of direction, in mechanics, is ufed for the product of the velocity of the common center of gravity of a fyftcm of bodies, by the fum of their manes. In the collifion of bodies, the quantity of Direction is the fame before and after the impulfe. Bernoulli^ Difcours fur le move- ment. Oper. torn. 3. p. 32 & 56. DIRECTOR, (Cycl.) infurgery, a grooved probe, to direct the edge of the knife or fciflars in opening finus's or fiftulas, that, by this means, the fubjacent veffels, nerves, and tendons, may remain unhurt. Sometimes one end is made in form of a fpoon, to contain powders to fprinkle upon wounds or ulcers. Sometimes alfo it is forked at the end to divide the frasnum of the tongue. He'yler's Surg. Introd. Sec. 36. DIRECTRIX, in geometry, the line of motion, along which the defcribing line, or furface, is carried in the Genefis of any plane or folid figure. It is otherwife called Dirigent. See Dirigent, Cycl. DIRIBITORES, among the Romans, officers appointed to di ftribute tablets to the people at the Comitia. See Comi tia, Cycl. DIRITTA, in the Italian mufic, a term intimating that the piece is to be played or fung in conjoint degrees. Thus, Contrapunto alia Diriita, according to Angelo Berardi, is when one is obliged to raife or fall the voice by the fame degrees, i.e. by an equal number afcending or defcending, without making a leap, even of the interval of a third. Brojf. Diet Muf. in voc. DISARM, in the manege — To difarm the lips of a horfe, is to keep them fubject, and out from above the bars, when they are fo large as to cover them, and prevent the true preffure or appui of the mouth, by bearing up the bit, and fo hindering the horfe to feel the effects of it upon the bars. Guil. Gent. Diet, in voc. DISBOSCATION, Dishofcat'io, a turning wood-ground into

arable or pafture, an affarting. See Assart, Cycl. DISCEIT, in our old writers. See Deceit and Deceptione. DISCOBOLI, A'fftoffcAo/, among the antients, an appellation given to thofe who gained the victory at the Difcus. Hofm. Lex. in voc. See Discus, Cycl. DISCOIDES Fifada, in natural hiftory, the name of a genus of the echinodermata, or fea hedge-hogs ; the periphery of the bafe of thefe is exactly round, and the body of a convexo-con- cave figure. The principal fpecies of this genus is the fubucu- lus, which has fometimes a rofeaceous top, the lines being very neat and elegant, fometimes a plain and fmooth top, fometimes is all over covered with extreamly minute and fine

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ftriae, and fometimes it is much flatter than at others. Klein's Echinoderm.

DISCRETIONE, in the Italian mufic, is ufed to direct the fin- ger or player to execute his part with care diligently.

DISDIACLASTIC Cryjlal, in natural hiftory, a name given by Bartholine, and fome other?, to the pellucid foifile fubftance more ufually called from the place whence it was firft brought, Ijhnd eryfial ; though properly it is no cryftal at all, but a fine pellucid fpar, called by Dr. Hill from its fhape parallello- pipedum. See IsLAND-Crjp/rW.

This cryftal is met with in other places befide I/land, but not fo plentifully. It is there found in great abundance all over the country, but is particularly plentiful in a mountain, not far from the bay of Roezfiord, where the fineft and moft pellucid pieces are found on digging. The mountain lies in 65 degrees latitude, and has its whole outfide made up of it ; but, though this makes a very bright and glittering appearance, it is not lb fine as that which lies at a little depth, and is met with on open- ing the furface. This is generally taken up out of the earth in maffes of a foot long, and its corners very frequently are terminated in thefe large maffes, by a fort of cryftals, very different in figure and qualities from the reft of the mats. The ftone itfelf is of a parallellopiped figure ; but thefe ex- crefcences are either fingle pyramids affixed to columns, like common cryftal or double pyramids, with or without columns between. The ftone itfelf is foft ; thefe are hard, and cut glafs ; the ftone calcines to lime in the fire, thefe run into glafs ; in fhort, the ftone itfelf is true fpar, and thefe are true cryftal : befide thefe, there fometimes grows out of the ends of the larger maffes a pure and fine abeftus. This likewife is the cafe fometimes in the fpar, found about Barege in Erance and fliews how nearly together the formation of bodies wholly different from one another, may happem The General fi- figureof the ftone is parallellopiped ; or, as fome exprefs it, rhom- boide ; and it retains this not only while whole, but alfo when bro- ken to pieces. Every fragment it naturally falls into, though ever fo fmall, being truly of that fhape. But it is remarkabTe, that in fome places of this mountain, the fame fort of matter is found in form of triangular pyramids, all which have the fame property of the double refraffion with the parallellopipeds of the fame fubftance ; fo that the original error of fuppofing its qua- lities owing to its fhape, is refuted by this, as well as by the trials made with other pellucid bodies of the fame figure, which do not fhew this remarkable property. Bartholine de Cryftal-Ifland. Phil. Tranf. N°6y.

The ifland cryftal is electrical, and when rubbed will draw up ftraws, feathers, and other light fubftances, in the fame man- ner that amber does. Ir is not fo hard as to endure polifhino-. The fides, however, are of an extreamly fine natural polifhj which is moft perfectly feen on breaking a thinner piece nim- bly between the fingers : for where a larger mafs is ftruck with a hammer, the percuffion has not the fame efibfl upon every part, nor is refilled equally every where ; and therefore the broken furfaces have often fome of the plates, or thin laminae of which they confift, raifed up, and become fcabrous and' rough by that means. The whole body is rather clear than bright : it is of the colour of limpid water ; but that colour, when it has been wetted, and dried again, becomes very much duller; and hence, it is, that the outer furfaces of the pieces, which lie on the outfide of the mountain, are ufually very dark and dull in comparifon of the others that it fhews when broken ; the rains and fnows often wetting and drying again upon it. When the furface is bright, there often appears the figure of a rainbow, with all the colours on it. The angles of the regular pieces are not pointed alike ; all the flat fides being obliquely inclined to one another. The oppofite plains are always parallel in this cryftaline prifm. Two of the plain angles are always acute, and the other two are always obtufe, ' and never any of them is equal to the collateral angles of the inclinations. The objeefs (een through it appear fometimes, and in certain pofitions of the prifm, double ; and, the diftance between the two images of the object, is always greater or left according to the largenefs or fmallnefs of the prilm, info- much, that in thin pieces of it, the difference of the double image almoft vanifhes ; and it has been hence faid, by fome, that only thick maffes of this ftone had the property. The objeel appearing double, both images appear with a fainter co- lour, and fometimes one part of the lame fpecies is obfeurer than another ; and, to an attentive eye, one of thefe images will always appear higher than the other. In a certain pofition of the ftone the image of the object feen through it appears only fingle, as through any other tranfpa- rent body ; and there is, on the contrary, a particular pofi- tion, in which it appears fix-fold. If any of the ob- tufe angles of this prifm be divided by a line into two parts, and the vifual rays pafs from the eye to the object through that line or its parallel ; both images of the objedf will meet in one, either in that line, or in one parallel to it. Whereas objeefs feen through diaphanous bodies, are wont to remain in the fame place, in whatever manner the tranfparent body is moved, nor does the image on the furface move, unlefs the objedt itfelf be moved ; in this particular pellucid body,

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