DIACRITICAL MARK. 19-4 DIAGONAL. respectively; and the sign « also usually denotes n Ion}; Miund, as it did in Greek. In many mod- ern English seicntilic worlds the aeule accent ['] is used to denote a short accented vowel, and the grave accent ['lis used to denote a long ac- cented vowel. So the scheme of diacritical marks used in this Encyclopaedia is in very general use to indicate the sounds here denoted b.v tlieni, being essentially the same as those employed in Webster's Intern.itional Dictionary, and in vari- ous other preceding or abridged editions of the same work, and in the majority of the school books of the country. The system of the Century Dictionary is in many respects quite dilVerent ; and that of the great English dictionary edited by Dr. JIurray {A A'eir j^nglish Dictionary on Uis- lorittil J'riitciplcs) is still dilVerent, and ex- tremely complex. The system used by the Stand- ard Dictionary contains fewer diacritical marks, the dilferentiation being obtained by the use of the alphabet arbitrarily devised and selected for use by the American Philological Association. See the articles Piioxetks ; Pronvxci.tiox, etc.. and for the various diacritical marks em- ployed in any language, consult a grammar of that language. DIADEM (Lat. diadema, Gk. ctiii/fia, dia- di'iiui, fillet, from oiaiiiv, diadeiii, to bind round, from <5/d, dia. through + <'t<i', dcin, to bind I . The name given to the fillet of silk, wool- en, or linen which served as the distinguishing ornament of kings. It was generally narrow, being only a little broader on the forehead. The diadem of Bacchus, as it ajipears in ancient sculp- ture, was a plaited band going round the fore- head and temples, and tied behind, with the ends hanging down. Among the Persians the diadem was bound round the tiara or turban, and was of a blue color, worked with white. The early Roman emperors refrained from using this orna- ment, in order not to call up recollections of the hated kingly office. Diocletian was the tirst to introduce it again. DIADEM SPIDER ( so called from the mark- ingi. 'I'lu- iniiiiiion cross-spider iAifiiojic dia- dcDio 1 common everywhere in European gardens. See SpiOKi!. DI'ADU'MENOS (Gk. 6iai'iol/ievo(, diadou- i»c)in.<;, binding rnuml. from iiafe'iv, diadcin. to bind round). A ccUl>rated statue by Polyclitus, representing a youthful athlete binding the fillet about his head. It is sujiposed to be a pendant to the "Doryphorus." The best reproduction ex- tant, now in the British Museum, is of Roman origin and was found near Vaison, France. DI.iERESIS, di-cr'c-sis. See Di.cbitical ^I.AP.KS. DIAFOIRTJS, d^'A'fwii'rus'. A ridiculous quack in MoliSre's l-^c maladc imafiinaire, whose son Thomas is a suitor of Argan's daughter, Angt'lique. DI'AGEOT'ROPISM (Ok. 6i/,. dia, through + yv- .'"'■ earth + rpiros, iropos. a turning) . That form of geotropisni, i.e. sensitiveness to gravity, wherein the bending organ come.", to grow in a direction at right angles to the direction of gravity. Rhizomes and runners of many plants possess this property. Sec Geotropism. DI'AGNO'SIS (Gk. diAyi'uaic, diagnosis, <liscriniinatinn. from iiayipuoKriv, dinriigiioslcin, to discriminate, from -'"i ilin. through -f- yip^- OKeiv, gigiwshcin, to know). The determination of the nature of a disease as well as of the con- dition of the organ or tissues atlVcted. This is the most important and dillicull element in the pr.ic- tice of medicine. The methods of diagnosis are based on a study of symptoms, such as chill, fever, pallor, delirium; and i>liysical signs, such as are appreciated by examination of the throat, chest, abdomen, eyes, urine, etc.. with the aid of the thermometer, stethoscope. micro<co])e, oph- thalmoscope, electric battery, etc. To learn to make a diagnosis, the pupil must study disease at the bedside, and diseased and normal tissues, llnids, and organs, in the autop>y room and the laboratory, following the course of symptoms and signs from the invasion of disease to recov- ery or death. DI'AGOM'ETER (Gk. diayc(v, diagein, to lead thniugh. from <5ii, dia, through -|- ayetv, agein, to lead -f /lirpov, mvlion, measure). A modified form of electroscope, invented by Rousseau, in which a dry pile is employed to measure the amoiuit of electricity transmitted by dilTerent bodies, and thus determine their eon- ducting power. The practical application of the instrument was to determine the purity of cer- tain substances, such as olive oil. whose con- ductivity varies with an admixture of other oila or substances. The instrument consists of two small metallic plates, one of which is fixed while the other is fastened to the extremity of a mag- netic needle. When at rest the two plates are in contact, but luider the influence of a charge of electricity they tend to separate and the time required for them to reach a maximmn position depends on the conductivity of the substance through which the current passes. DIAG'ONAL (Lat. diagonalis, from Gk. Aa- yijiiof, diagOtiios, diagonal, frnni tha, ilia, throtigh -f- yuvla, gOiiia. angle). In plane geometry, a straight line joining any two non-adjacent ver- tices of a rectilinear figure. A line between (wo adjacent vertices would coincide with a line of the figure, hence a triangle has no diagonal. An ordinary four-sided figure, a quadrilateral, has two diagonals: a ])entagon. five: a hexagon, nine, and so on. The general expre^^sion for the number of diagonals in such figures of »i sides is "'""TLJ', where »! represents the number of sides. Thus the number of diagonals in a dndeca- 12(12— .3> gon (q.v.), a polygon of twelve sides, is .j - = .'54. If the polygons are general, that ia, composed of lines of indefinite extent inter- secting in the maximum iuiml)cr of points. the» number of diagonals is given by (ne formula I . ! ^, where »i is the nunilwr of sides; e.g. 8(ft — 4.)! ' in a general dodecagon the number of diagonals is 12 I _,^_ 8(12 - 4) I — l*^*'- A diagonal of a solid bounded by limited planes is a line joining any two vertices so situated that the line does not lie in any face. 'I he number of diagonals in any regular poly- hedron (q.v.) is given bv the fornuil.a )is • I «« — .>' (s — 2) _« 1 * •j if-^ r, where n is the nimi- ber of faces, s the number of sides of a face, and r the number of faces grouj^jrl about the
