Page:Cyclopaedia, Chambers - Supplement, Volume 1.djvu/603

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by means of their mufcular coats, contract tliemfelves to the fame dimensions, or lie in folds or corrugations, which is much let's probable.

On the other hand, when the ribs are elevated, and the dia- phragm bears downward, the air rufhing into the lungs, (hoots out the cartilaginous rings, and divaricates the branches of the trachea, and by them extends and divaricates the feveral divifions of the pulmonary artery and veins, and thereby lengthens and enlarges their cavities. This enlargement of their cavities is very confiderable, not only upon the fcore of the addition, which they receive in length thereby, but alfo on account of their divarication ; for whereas, when the ribs are deprefled, and the lungs fubfide, the blood vefTcls are not only contracted, but their branches, which are exceeding nu- merous approach one another, and lie in juxta pofition, by "which their cavities are very much compreffed and ftreightned : when the ribs are elevated and the lungs turgid with air, not only the fibres, by which their coats in the opnofite ftate were contracted, are extended ; but thofe innumerable veflels, which lying before in lines almofl contiguous to one another, com- prefied each other, making an acute angle at their junctures, are divaricated and feparated from each other, and make an obtufe one, whereby their channels are widened. Thus a pafTage is opened for the blood from the right ven- tricle of the heart to the left, through the lungs, to which it could not otherwife pafs ; and the oppofition, which the blood contained in that ventricle muft otherwife have had made to its conftnetion Is taken off, and the fyftole thereby facilitated; nor is this all, for the diaftole being caufcd, as is certainly and demonftrably the cafe, by the force of the blood ruining into the ventricles ; tin's ampliation and extenfion of the pulmo- nary artery is a fort of check or counterpoife to ir, and pre- vents an endeavour towards two contrary actions at once, which would neceflarily fruftrate both : for the heart being a fpringy and compreflible body, whofe proper action, which is contraction, depends upon the influx of certain fluids into its fibres and fubftance ; and containing befide a fluid in its ven- tricles, or great cavities, in one of which is the mouth of this artery, the action of this veiTel muft in a great meafure re- fembletbat of a fyringe, whofe extremity is immerfed in wa- ter. The enlargement or expanfion of the channels of the artery, anfwering the drawing of the embolus, as the con- ftrictive motion of the mufcle of the heart, does the preffure of the atmofphere on the furface of the water ; the one mak- ing way for the fluid, and the other forcing it, to flow where the refiftance is leaft. In this fenfe we may allow a fort of attraction to the pulmonary artery, depending wholly upon the action of the intercoftal mufcles, and diaphragm, which we muft therefore confefs to be very ferviceable and inftru- mental in promoting the fyftole of the heart. Phil. Tranf. N° 281. p. 1222.

DIATONIC (Cycl.) — The Diatonic genus was by the antients divided into two fpccies : the molle, and the tntenfum. The laft is in daily practice. It is commonly faid to confift of two tones and a femi-tone : but, to fpeak exactly, it con- fifts of a femi-tone major, a tone minor, and a tone major. Phil. Tranf. N° 481. p. 212.

We find it accurately defined by Didymus, in Ptolemy's harmo- nics publifhed by Dr. Wallis. Vid. Walhs Oper. vol. 3. p. 92. The numbers by which Didymus exprefies its intervals, are, Ix^x -rf — f. Ptolemy, indeed, makes the Diatmicum inten- ium, to be exprefled by V x |. x |4 = i ; but, it is plain, this is only tranfpofing the tones major and minor, which makes no effential difference, nor is it Sufficient to conftitute a new fpecies. But the firft of the before-mentioned fpecies, the Diaicniami moUe y has not, till lately, been accurately defined by any au- thor. Its component intervals, according to Dr. Pepufch, are, the feini-tone major, an interval compofed of two femi- tones minor, and the complement of thefe two to the fourth ; which complement is equal to a tone major, and an enhar- monic Diefis. Phil. Tranf. N° 481. p. 271, 272. Befides, the two fpecies of the Diatonic mentioned by Ariftoxe- nus and Euclid ; Ptolemy, and other antient muficians, have left us feveral different Diaontlc divifions of the tetrachord ; fuch are the Dianotic of Arcbytas, of Eratofthenes, and of Didy- mus, which laft agrees perfectly with the truth of mufical pro- portions. Ptolemy himfelf gives us no leis than five different Diatonic;, by the names of molle, tonicum, ditonkum, intenfum, eequabile. Phil. Tranf. N J 481. p. 271. See Genus. But, except one (the intenfuni) they arc all inconfiftent with the true theory of muTic ; which admits of no numbers, or proportions, but 2, 3, and 5, and fuch as arife from thefe primes. Indeed Ptolemy's tetrachords are fo mif- tuned, that Salinas has charged him with having had no ear. Vid. Phil. Tranf, ibid. p. 267.

DIATONUM, Aia.Tovct>, in the the antient mufic, is ufed for the Diatonic genus. See Diatonic.

DIATR^LTA, a word ufed by Pliny, and other of the antient Romans, to exprefs a fort of cups and vales, which were of great value, and only feen at the tables of the great. They were pellucid and colourlels, and cut into various forms, and were often engraved upon with figures expreffiye of the deeds Supfl. Vol. I.

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of honour 6f the family who poiTeffed them. The firft Dia- treta were made of pure cryftal of the rock, and the working- of thefe rendered them very expenfive ; but afterwards they were made of common white glafs, and funk greatly in their price and value. The antients were very nice in their diftin- ctions of the feveral kinds of cryftal. They termed the' pu- reft and fineft of all acentatum,\ and the others, which were fubjed to blcmimes and foulneffes of feveral kinds, they call- ed by names expreffive of therm There was nothing they fo much feared in the pieces they felected for this work, as what they called an over hardnefs, that is, a brittlenefs, which made the veffel often fly under the engraver's tool, after it had been formed into fhape at a great expence: for this reafon they were cautious of ufing the very brighteft and cleareft manes; for they often found thofe fucceed beft, which had fome of thofe flaws which we call hairs in them. Thefe they thought the tougheft pieces of cryftal, and thefe flaws they eafily concealed among the ftrokes of their work. See the articles Sal and Nubes. DIATYPOSIS, AtcnvTmnt, in rhetoric, the lively defcription of a thing, fetting it, as it were, before the eyes of the audience. Thus Cicero, vn. in Verr. Ipfe iftfiammatus feeler e & furore, in forum veniti ardebant oculi\ toto ex ore crudelitas amnebaU c5V DIAULION, in antiquity, a defignation given to a perform- ance on the antient ftage with the flute alone. DIAULODROMI, Atav^ff ipoi, in antiquity, thofe racers who turned round the meta, or goal, and finifhed their courfe at the career, or place of ftarting. The Diaulodromi always took a fhort breathing or reft, when they arrived at the meta, before they fet out again for the career. Pitifc. Lex. Ant. in voc. See Carcer. DIAULOS, in antiquity, the name of a particular kind of race, wherein the racers always returned to the place from whence they ftarted, and were called Diaulodromi, Pitifc. Lex. Ant. in voc. See Diaulodromi. Diaulos is alfo ufed to fignify a diftance of two ftadia. Id„

ibid. DICE Marie, in husbandry. See the article Ma rle. DICERATON, in the writers of medicine, a name given to a ! coliyrium mentioned by Celfus, and thus named from «££{, a horn, burnt hartfhorn being a principal ingredient in it. DICHOR/EUS, in poetry, the foot of a Latin verfe confiftin^ of four fyllables; of which the firft is long, the next fhort, the third long, and the laft fhort. It is a double Chorcom, as cbmpr'' bare. DICHOTOPHYLLUM, in botany, the name by which Dil- lenius, and feveral others, call the hydroceratopb'yUum of Va- illant; and fome other writers, a genus of plants charactered by Linnaeus- in his genera plantarum under the name of Cera- topljylhn. Dillen. Gen. 3. See Ceratofhyllon. DICKER, or Dicre, Dicra> in our old writers, a quantity of leather confifting of ten hides. Blount. Some derive the word from the Greek ^s^, ten. We find the word Dicra applied to other things befides lea- ther; thus, Civitas Gloucq/lrite reddebat xxxvi Dicras ferri, which is interpreted 36 Dickers of iron, ten bars to the Dicre. Gale's Hift. Brit. 766. ap. Blount. DICROTUS, in natural hiftory, a word ufed by the antients to exprefs the deer or ftag when in its third year's growth. It was called Nebus by the antient Greeks in the firft; year, Put- tolea in the fecond, Dicrota in the third and in the fourth, and all its life afterwards Cerafles. Dicrotus, in the medicinal writings of the antients, the epi- thet given to a peculiar fort of pulfe, which Dr. Nihill calls very properly in Engliih the rebounding pulfe. In this kind of pulfe the artery beats as it were double; and it is efteemed a certain fign of a future critical haemorrhage by the nofe. When the rebounding pulfe is perceived at about every thirtieth puliation, the haemorrhage ufually follows in about four days after ; when it recurs at every fifteenth pulfation, the haemor- rhage generally follows in three days; when every eighth pulfation, it is to be expected in two days and a half; and, fi- nally, when it recurs at every fourth, third, or fecond pulfa- tion, or is continual in every one, the haemorrage is to be expected within four and twenty hours. Sometimes nature runs regularly through all the before-mentioned progreiTions of this critical pulfe from its firft appearance at every thir- tieth ftroke, to the fingle pulfation ; and in this cafe the hae- morrhage is feen gradually approaching, and happens regular- ly as expected : but fometimes fhe haftens or delays it; and then the pulfe fhifting in its indications, it cannot be judged of with any certainty ; when the artery rebounds upon the finger with great celerity, and very briskly follows the firft ftroke, the haemorrhage is juft at hand, and will appear on the pati- ent's blowing his nofe.

The quantity of the haemorrhage may be guefled from the ftrength of the rebound in the pulfe, and as the blood dif- charges nfelf, this fymptom in the pulfe gradually goes ofF; and if after the haemorrhage it mould be perceived again, it is a fign of another crifis of the fame kind. Final- ly, when the rebounding of the artery is more evident in one 9 F wrift