DIORA'24A, a mode of painting or scenic representation, invented by two French artists, Daguerre and Benton, and recently brought forward as a pub lic exhibition in all the principal cities of Europe. The peculiar and very high degree or optical illusion produced by the diorama depends upon two princi pies; the mode of exhibiting the paint ing, and the manner of preparing it. With respect to the first of these, the spectator and the picture are placed in separate rooms, and the picture viewed through an aperture, the sides of which are continued towards the picture, so as to prevent any object in the picture room from being seen excepting the painting itself. Into the room in which the spectator is placed no light is admitted excepting what comes through this aper ture from the picture; he is thus placed in comparative darkness, and also (which contributes to the effect) at a consider able distance from the picture. The picture room is illuminated from the roof, which is glazed with ground glass; and the picture so placed that the light falls on it at a proper angle to be reflect ed towards the aperture. The roof, which is invisible to the spectator, is provided with an apparatus of folds or shutters, by which the intensity of the illumination may be increased or diminished at pleas ure, and so modified as to represent, with great effect and accuracy, the dif ferent accidents of light and shade, or the changes of appearance depending on the state of the atmosphere ; as bright sunshine, cloudy weather, or the obscuri ty of twilight. The second principle con sists in painting certain parts of the pic ture in transparency, and admitting a stream of light upon it from behind, which, passing through the picture, pro duces a brilliancy far surpassing what could be obtained by illuminating the picture in the ordinary way, and renders the relief of the objects represented much stronger and more deceptive.
Renee, the diorama is peculiarly adapt ed for representing architectural objects, as the interiors of cathedrals, ,X.c. In order to render the exhibition more at tractive, it is usual to present more scenes than one. This may of course be effected by removing one picture and substituting another ; but with a view to prevent the illusion from being impaired by the accidents incidental to scene shifting, a different method is sometimes resorted to.
DI I'll"FHONG, the union of two vow els pronounced in one syllable. The sound is not simple, but so blended as to be con sidered as forming hut one syllable, as noise, bound, joint, Ac.
Di PLO'MA, is written document, con ferring some power, privilege, or honor, viz., an instrument or license given by colleges, societies, &c. to a clergyman to exercise the ministerial function, or to a physician to practise the profession, he., after passing examination. or admitting him to it degree.—Every sort of ancient charter, donation, bull, is compre hended by writers on diplomaties under the name diploma. The term is derived from the earliest charters of donation with which we are acquainted, those of the early Roman emperors having been inscribed on two tablets of copper joined together so as to fold in the form of a book. Writings of earlier date than the fifth century are generally on leaves of the papyrus„ or bibles .,Egyptiaca; those of a later period on parchment. The form and character of the diploma granted by the sovereigns, prelates, nobles, &c. of modern Europe, varied from age to age ; and the knowledge of these variations forms an important branch of the science of diplomaties.