DIOPTRICS. 



DIPHTHERITE. 



expeditions of later Macedonia wcr mythicallv typified) celebrating 

 the triumphs of the conquest of India." (' Ancient Art,' p. 4: 



On the form and dress of Dionysus lmort all the ancient tartfancaM 

 hare been oollectnl by K. G. Kclion in an inp-iiioim diiwertat i..n ..n the 

 oastume of the character* in the Bacchic uf Kuripidea ; and by Mullrr 

 a* above. The earliest forum of the god represented him as a nun of 

 mature age, with luxuriant curling hair, Imtiml by tln> mitra. with a 

 flowing beard, and open expression of face, and enveloped in ample 

 drapery : when thi form occnn in late example*, it is maO* termod 

 the Indian Bacchus. Many bust* of this kind occur, an ibo many 

 example* in relievo. Later he was represented an a young man with 

 an effeminate face (fnMWpfM, Baoch. 858 ; Euseb. 'Chnm.' p. 2lM, 

 with long blond hair (Bacch. 466. ' Cyi !.' >'"': with a fillet on his head 

 (Strabo, XT. p. 1038), or an Jvy crown (' Cvcl.' 693), with a long purple 

 robe and a nebris (deer-skin), and with a thyrsus in his hand. 



[The Youthful Dionysus attended by * Fann, from a bas-rclicf in the British 

 Museum.] 



U 



The Greek Dionysus seems to have been confounded by the Roma 

 poets with Liber, on early Italian deity, who presided over the culti- 

 vation of corn and the wine, aud who waft associated with the worship 

 of a female deity Libcra and Ceres. Libera came, therefore, according 

 to the Roman custom of uniting a female with a male divinity 

 [BELLONA], to be regarded as the feminine counterpart of Bacchus; 

 and instances occur where they arc represented united in one figure. 



[Itucliui nnd Libert, from the Biltiih Museum.] 



Bacchus is also spoken of liy Roman ]>oets,ond occasionally represented 



iptors, as androgynous, or partaking in himself of Ixith sexes. 



Hut a clearer notion will lie obtained of the artistic idea of Dionysus 



and his associates from a visit to the British Museum, than from any 



description within the narrow limits of a. cyclopiedia. In the 



Gnoco-Roman Saloon will l-e found a numU-r of Bnc< 1 Mtinns, 



arranged together under the title of the Dionysiac Cycle, including 



statue*, busto, and masks of Dionysus, both bearded and youthful; 



i if the gut and various (wrsonages; statues of Libera, Pan, 



. Satyr*, and Bacchantes, with rclievi of iJionysian ] micesnions, &c., 



while in the magnificent collection of fictile vases in the Vace Rooms 



nierou* |niiitiiigi of scenes from the Diunysia. 

 IiKHTIlle'S. |llni.,; Hi i IIA.TIOS.] 



I'lnKA'M A. fioin tl i el Jiop? v, to sec through, a mode of 



painting and scenic exhibition inveiiti-d by t we. Kreiich artists, Dogucrre 

 anil IJouton, which, although it does not jiosscss some of tin- advantages 

 ni tliu panorama, producer a far greater degree of optical illusion, and 

 is therefore much better adapted for architectural and interior views. 



The peculiar effect of the diorama arises, In a considerable measure, 

 from the contrivance employed in exhibiting the painting, which is 

 viewed through a large ajwrture or proscenium. Beyond this opening 

 tun- in placed at such a distance that the light is thrown upon 

 it, at a pro]r angle, from the iW. whi.-h i glo/.ed with coloured 

 glass, and cannot be awn by tin- |.titor. Besides the light K-ing 

 thus concentrated upon the picture, the effect Is materially increased 

 by the spectator being in comparative <Urknesn. ivceiving no other 

 OJAi than what is reflected from the surface of the jaintiiiK itself, and 

 fitting at some distance from the picture. The contrast occasione.1 by 

 confining the light to tlie pieture, and the exclusion of all other object* 

 of vision, save those represented in the painting, so that the eye has no 

 immediate standard of compejison between them and real ones, give to 

 this species of exhibition BO much force that a very moderate degree of 

 light will suffice to show the painting. Hence the light may be 

 diminished or increased at pleasure, and that either gradually or 

 suddenly, so as to represent the change from ordinary daylight to sun- 

 shine, and from sunshine to cloudy weather, or to the obscurity of 

 twilight; also the difference of atmospheric tone attending Hum. 

 These transitions, in regard to light and atmospheric effects, are pro- 

 duced by means of different folds or shutters attached to the glazed 

 ceiling, which are so contrived that they may be immediately 

 or closed to any extent, thereby increasing or diminishing the light 

 just as required, and otherwise modifying it. Further than thin, some 

 parts of the painting itself ore transparent, and on them the light can 

 occasionally be admitted from behind, thereby producing a bi: 

 for exceeding that of the highest light* of a picture upon an . 

 ground, which can be mode to appear vivid and sparkling only by 

 contrast, not by any jHieitive increase of light on those parts of the 

 . The combination of transparent, scmi-tramsparent, and opaque 

 colouring, still further assisted by the jx>\ver of varying both the 

 effects and the degree of light and shade, renders the diorama, in com- 

 petent hands, perhaps the most perfect scenic representation of i 

 and adapts it peculiarly for moonlight subjects, or for showing such 

 Ml in the landscape as sudden gleams of sunshine aiii 1 

 arance, as well as for architectural interiors. The diorama was 

 exhibited first at Paris in 1822, and then in London in 1823, where a 

 spacious building was erected for the purpose in the Regent's Park : 

 but here, though at first very successful, it after a time ceased 

 to attract, and was discontinued, and the building was converted into a 

 Baptist chapel. 



DIOSMIN. A non-azotised bitter matter found in the leaves of 

 the Diotma crenata. Its composition is not known. 

 DIP; DIPPING NEEDLE. [MAGNETISM.] 



D1PHENINE (C M H W N,). A yellow crystalline alkaloid derived 

 from In 



DI-1'HENYL, a double prefix, used in organic chemistry to denote 

 the presence of two equivalents of phenyl in the body to which it U 

 immediately attached : thus tlijihcityl-carbamidc signifies carbamide con- 

 taining two equivalents of pheuyl. Any chemical substance the name 

 of which begins with this prefix, and which is not found in ita alpha- 

 betical position, will, if of any importance, be found described under 

 the name without one or both of the prefixes : thus, diphtnyl-oxamidc 

 will be found described either under PiiKNYi.-OxAMlUE or OXAMIDE. 



I> I PI ITU liKlTE or PlI'HTHERITIS (from Si<t>eipa, a. skin or mem- 

 brane), a term applied by H. Bretonneau and other French writers to a 

 peculiar inflammation of the mucous membrane of the throat or 

 pharynx, which is accompanied by the production of a false mem I 

 This disease first attracted attention at Tours in France, where it 

 prevailed as an epidemic in 1818. It subsequently appeared in other 

 towns in France, and alarmed the inhabitants of Boulogne in 1856. 

 It has also been seen in India since its discovery and description by 

 Bretonneau. No cases seem to have been accurately observed in this 

 country till 1857; but since that time it has broken out in many parts 

 of England, and presented its most characteristic symptoms. Vhen 

 this disease was first described, it was regarded by some writers in 

 this country as a variety of croup, and by others as a form of 

 fever. Now that it has appeared, few observers could be found who 

 would not agree that it is a disease t gcutrit. The invasion of this 

 disease has been looked on with greater anxiety, as there seems to be 

 little doubt of its belonging to the contagious or communicable class. 

 It is al>o very fatal, and already a large amount of mortality has been 

 caused by it in this country. 



The distinguishing feature of this disease is the formation of a fake 

 membrane upon the surface of the mucous membrane of the fauces. 

 This membrane is of a whitish or ash-gray colour, and frequently 

 extends forwards from the pharynx and tonsils to the soft palate and 

 into the nostrils, and backwards into the oesophagus. It is seldom 

 found in the larynx and the trachea, and in tliis respect it differs from 

 croup, and may be easily distinguished from it. When the membrane 

 is found in the larynx or trachea, it is always subsequent to ita 

 appearance in the fauces, and in these cases it is most fatal. At the 

 commencement of the dimi e. tl ,< membrane is seen in the form of a 

 white spot on the pharynx or 10 which it gradually extends 



all around. As ii ilie membrane romcs away in sputa or 



presents fissures, through which the mueous immliiane n : 

 a derj) 1 1 1 01 i M n of a purplish nnd claret colour. Duriug tue progress 

 of the disease the cervical and submaxillary glands become swollen, 



