ID'DINGS, 'JOSEPH PAXSON (1857— ). An American geologist, born in Baltimore. Md. He graduated at the Sheffield Scientific School of Yale in 1S77, was a graduate student and a. sistant in mechanical drawing and surveying there until I878, and continued his studies in geology and microscopic petrography at Colum bia 1_ niversity and Heidelberg. From Iti50 until 1892 Ii was in the service Of the United stales t:eologieal Survey, to which he returned in 1895. In 1s92 he became assistant professor, and in 1s:13 professor, of petrology at the University of Chi cago. llis t:overnment explorations were de scribed in many reports and contributions to scientific journals. Among his more important writings are 7/u A ((tare and Origin o/ Litho and the Lamination of .1 eld L111'418 ( ) reprinted from the .1 rnerican Journal if 1111 1,0// the !) e, lomat tit of crystalli:a111,11 in the I !Imms Rocks of Nee. t 1S55), with Ar mild Hague; and The Origin of Igneous ii l:s (159•). in the Ruth t in of the Washington Philo sophical Society.
IDE (Norweg., `wed. id, roach). A fish ( u eisens ides), closely allied to the roach. It in habits the lakes of the northern parts of Europe, and ascends rivers in April and May to spawn. It is excellent fur the table. A gold-colored va riety, called 'orle,' is bred in Cermany, and is sold extensively for ornamental aquariums.
IDEA (Lat., from (1k. iJia, form, from Iii idein, to sit'; •onn«.ted with Lat. rid, re, to Ski. rid, AS. triton. Eng. mit, to know). The term 'idea' has undergone a radical change of meaning in the history of psycholol_ry. "Employed by Plato to express the real form of the intelligi ble world. in lofty contrast to the unreal images of the sensible, it was lowered by Descartes, who extended it to the objects of our consciousness in general" (Hamilton). In modern philosophy the word has a distinctly empirical flavor. Locke (q.v.) defines idea ;1:4 "Wilat,011Ver is the object of the understanding when a man thinks," "that which the mind is applied about whilst think and the intellectualistic tendencies of the English Assoeiationist school or lw.:As) made 'idea' alnio.A. ..quivident to what
is now termed 'mental roues,* (q.v.). In current psychological usage the word is either taken in a wide sense to denote the "conscious representation of some object or process of the external world" (Wundt ). thus covering perception (q.v.), ideas if memory. and ideas of imagination: or it is ro-stri•ted to the two latter categories, and op posed to perception. as a strictly representative to a presentative Since there is no essential psychological difference between 're-pres entation' and 'presentation,' the first and wider application of the term is preferable.
An idea which has been formed. after the ma il• ber of a composite photograph. from many ideas of similar character, and which has thus lost definiteness of detail. while it is liable to asso eiative arousal at the hands of a large number of other ideas, is termed an 'abstract' idea. (See ATISTRACTION.) When the abstract idea is spot and not pictorial—when, e.g., it. is a word— it is named a 'concept.' Ideational masses of complex but vague contents. which require the operation of active attention to bring their con stituents to separate recognition—such as our idea of the sentence that we are about to utter, or (on a still larger scale) our idea of self—are called 'aggregate' ideas. For ideas of memory and imagination. see those titles.
Consult: Sully, The Human Mind, vol. i. (Lon don. 1892) ; Ladd. Psychology. Descriptive and Explanatory (New York, 1894) ; James, Prin ciples of Psychology (ib., 1890) ; Titebener, Out line of' Psychology (New York, 1899).