Dipteris, a genus of Leptosporangiate ferns, section Mixtæ, formerly included in Polypodium, but now recognized as the sole living genus of the Dipteridineæ, a family which was largely developed in Mesozoic times. They are Indo-Malayan ferns with creeping rhizomes and long-stalked, fan-shaped, forked, leathery fronds.
Dipterocarpaceæ, an important order of Asiatic dicotyledonous trees, allied to the mallows (Malvaceæ). The different species produce a number of resinous, oily, and other substances; one, a sort of camphor; another, a fragrant resin used in temples; and others, varnishes; while some of the commonest produce pitches, and sal (Shorea robusta) yields valuable timber.
Diptych (dip´tik), in Greek originally signified the same as diploma, something folded; the double tablets of metal, ivory, &c., used by the Greeks and Romans. Diptychs became important in the Christian Church, in them being written the names of Popes, and other distinguished persons, who had deserved well of the Church, to be mentioned in the church prayers. Diptychs also often contained pictures of biblical scenes.—Cf. Sir W. Smith, A Dictionary of Greek and Roman Antiquities.
Dipyre (dī´pīr), or Mizzonite, a mineral—aluminium calcium sodium silicate—of the scapolite series. Its name indicates the double effect of fire upon it (Gr. di, double, pyr, fire) in producing first phosphorescence, and then fusion.
Diræ, one of the names under which the Eumenides were known to the Romans. See Furies.
Directors, persons elected to meet together at short fixed intervals and consult about the affairs of corporations or joint-stock companies, and to advise and assist the manager. These are termed Ordinary Directors, as in many companies there is a body called Extraordinary Directors, who have little or no business functions, and are chosen as a rule on account of their social position imparting a degree of distinction to the concern. Directors are appointed by a general meeting of the shareholders in the undertaking, and a certain number of them, usually a third, retire every year. Ordinary directors are granted a certain remuneration for their services. The duties and responsibilities of directors are defined by the constitution of the company, or by the various Acts of Parliament affecting joint-stock and other companies.
Direc´tory, the name given to a body of five officers to whom the executive authority in France was committed by the Constitution of the year III (1795). The two legislative bodies, called the councils, elected the members of the Directory: one member was obliged to retire yearly, and his place was supplied by election. This body was invested with the authority which, by the Constitution of 1791, had been granted to the king. By the Revolution of the 18th Brumaire the Directory and the Constitution of the year III were abolished. It was succeeded by the Consulate, with Napoleon as First Consul.
Direc´trix, a fixed line that is required for the description of a curve. The term is chiefly used in connection with the parabola, ellipse, and hyperbola, which are the loci of points that move so that their distances from a fixed point (the focus) are in a constant ratio to their distances from the directrix. The directrix of a parabola is a line perpendicular to the axis produced, and at a distance from the vertex equal to the distance of the vertex from the focus. Thus AB is the directrix of the parabola VED, of which F is the focus.