PSYCHOLOGICAL APPARATUS. 510 PSYCHOLOGY. Attention. The fluctuations of attention are mcasureil bv very faint auditory or visual stim- uli; e.g. by the ticking of a distant watcli, llie continuous fall of a little stream of sand, or the light gray rings on white ground produced by r<aation on the color-mixer of a disk of white cardboard, on which is drawn a broken black radius, Distribution or distraction of attention is studied by the complication pendulum — an in- strument which presents to the observer, at one and the same moment, impressions of sight, of sound, and of touch. The range of attention, i.e. the number of objects simultaneously appre- hensible by a single attentive ob.servation, is de- termined visually by the tachistoscopc, and audi- torily by the metronome. The tachistoscopc con- sists, in essentials, of a screen carrying words, figures, or letters, which can be displayed for a fraction of a second by a shutter, like the instantaneous shutter of a photographic caniiira. Other Insteuments. Apparatus employed in the study of the more complicated mental proc- esses have, as a rule, the special form given Ihem by individual investigators. There are several forms of menujnj appiimtus, the essential feature of which is the serial exposure of words, letters, etc., to be memorized by the observer. In work upon recognition, it is usual to ado))t some one of the pieces given under the headings Psychologi- cal Acoustics and Psychological Optics. Some- thing has been done, in the study of imagination, by aid of the symmetrical figures formed by folding upon itself a piece of paper upon which an inklilot has been made; recourse is also had to the suggestions aroused by printed sentences or paragraphs. Individual psychology' has its own materials, of specially prepared proof-sheets or ])ages of printer's pi, letter-patterns upon ruled cards, etc., etc. Finally, it may be said that the apparatus described in the body of the article above are, in general, the simplest of their kind; many more elaborate instruments have been de- vised, as e.g. for the study of rhythm. Every laboratory must possess a good stock of general supplies, for use with the above-men- tioned special apparatus. We may refer, in partioilar, to chemical and photographic ma- terials; electrical appliances — motors, cells, storage batteries, switches, keys, wires; mechan- ical supplies — tools, balances, materials for the construction and repair of simple instruments, standards, arms, clamps, etc., for the building up of complex apparatus; projection lantern, and wall charts. In the light of the above discussion, the figures of the plates will be largely self-explanatory. The sound pendulum was first invented by Fechner; it is figured in the form given it by Wundt. The combined color-mixer and canipim- •eter was devised by Hering. Figs. 2, .3. 4, fi, 7, 8 of this Plate are taken from Titehener's Experi- mental Psychology. The Appunn tonometer is a box containing reeds, differing by 4 complete vi- brations : it is used for investigations of sensi- ble discrimination, etc. The figure of Zwaarde- maker's olfactometer shows the appliances used for the simultaneous record of the observer's breathing curve. The Deprez signal is a time- marker, replacing the tuning-fork referred to in the text. Masson's disk is employed in experi- ments on the fluctuation of visual attention. Figs. 2, 4, 5, fl, 10 of this Plate are taken from Titehen- er's Experimental Psycliology ; Fig. 7 is from Sanford's Laboratory Course. Consult the authorities referred to under LAiiORATOKY, and es])eeially the catalogues of in- strument-makers listed in Titeheuer, Experi- mental Psychology (New York, 1901). See Dura- tion : Illi.siox. PSYCHOLOGICAL ASSOCIATION, .meri- CAK. A learned society organized in New York. July 8, 1892. and having its headquarters at Columbia University. Its object is the advance- ment of psycholog}' as a science, and it has a membership of one hundred and twenty-five. The society publishes an annual volume of Proceed- ings. PSYCHOL'OGY (from Gk. ^vxi, PK'jdie, breath, life, snul + - Xo7/a, -logia, account, from X^7ei>', Icgcin, to say). Psychology may be de- fined as the science of mind. More exactly, it is the science of mind considered for the sake of mental facts and processes alone, and apart from their values or eon.sequences. It is thus distin- guished from the other mental sciences: from logic, which is concerned with the truth or error of reasoning ])rocesses; from epistemology, which is concerned with the validity of perception; from metaphysics, which deals with the consistency an-d reference of fundamental conceptions; and from ethics, which is concerned with ideas in relation to their infiuenee upon conduct. Psychology is distinguished from all these, while at the same time it necessarily encroaches upon their terri- tory in considering the mental facts with which they also deal, what distinjiuishes |)syeliological science from the others being its point of view, which is primarily the observation and analysis of the innnediate ps3'chical phenomenon what- ever its nature. The most important works which ap|)cared be- fore the advent of modern philosophy, works which the modern psychologist cannot all'ord to neglect, are Aristotle's ti'eatise De .inima with its appendices, the Purni Xnliindia. and the Summa Theologian of the scholastic pliiiosopher Thomas Aquinas. For Aristotle's psychology, consult the works of Wallace (Cambridge, 1882) and Hammond (London, 1901). Carus, Ge- schichle der Psyehologie (Leipzig, 1808). and Harms, Geschichte dcr Psychologic (Berlin, 1878), have written general histories of psy- chology, but both are very incomplete. The two volumes of Siebeck. Geschichte der Psyehologie (Ciotha, 1880, 1884), extend only to Thomas Aquinjis. Dessoir has recently publislied the first part of a Geschichte der nciiercn drutschen Psychologic (2d ed., Berlin, 1897). The principal stages in the development of modern psychology may be characterized as the speculative or deductive, the empirical or asso- ciationist, and the scientific or experimental. The first anil third are preponderantly (icrman, the second English. The first may be said to culmi- nate in Hegel (consult Wallace. Hegel's Philoso- phy of Mind, Oxford. 1894). though it has con- tinued in the 'purely introspective' works of the Herbartian school. The second contains the great names of English philosophy, from Thomas Hobbes down to ,Iohn Stuart Mill and Alexander Bain. The cardinal defect of this psychologv; is its confusion of the logical or epistemological standpoint with the standpoint of psychology proper. It conceives of perception, e.g. as a sum or aggregate of least bits of knowledge, which it
