P3YCHROMETER 



PTERODACTYL 



477 



first random, reflex, instinctive, or merely expres- 

 sional, are brought within its operation. Fujther, 

 will grows side by side with reason and imagination, 

 is called into operation not by sense-presentation 

 only, but in response to images and concepts, and 

 can thus be regulated by reason. A double tend- 

 ency is at work in this development : the associative 

 and automatic tendency of acts frequently repeated 

 to become habitual ; and the intellectual tendency 

 by which ends and the acts tending towards them 

 are brought into rational order. In this way the 

 individual comes to act for permanent ends and 

 from fixed principles, and to develop a definite 

 character. 



LITERATURE. The first scientific treatise on psychology 

 was Aristotle's work De Anima. In modern philosophy 

 mi intuitional and spiritualist theory of psychology is to 

 lie found in Descartes and Leibnitz, an empirical and 

 materialistic theory in Hobbes. The Association-psycho- 

 logy, which traces descent from the psychological philo- 

 sophies of Locke and Hume, and from the physiological 

 psychology of Hartley ( Observations on Man, 1749), may 

 be read now in the works of James Mill (Analysis of the 

 Phttvimena of the Human Mind, 3. S. Mill's cd. 1869 ), 

 J. 8. Mill (Examination of Hamilton's Philosophy, 5th 

 ed. 1878), and A. Bain The Senses and t/ie Intellect, 3d 

 ed. 1868 ; '/ he Kmotions and the Will, 3d ed. 1880 ; Men- 

 tal and Moral Xcience, 3d ed. 1875 ). Belonging to the 

 game school, but conditioned throughout by the doctrine 

 of evolution, is H. Spencer's Principles of Psyckolugy 

 (2d ed. 1870-72). To the Herbartian influence is due 

 the exhaustive text-book of W. Volkmann von Volkmar 

 (Lehrbuch tier I'sychologie, 3d ed. 1884). Independent 

 views, which are yet influenced by Herbart, are worked 

 out by Lotze (Medicinische Psychologic, 1852; book iii. 

 of Metaphysics, Eng. trans. 1884; Microcosm.ua, Eng. 

 trans. 1885; Outlines of Psychology, Eng. trans. 1886) 

 : nd by J. Ward (article 'Psychology' in Ency. Brit., 9th 

 ed.). Experimental psychology is represented by the 

 works, among others, of Wnndt, Ebbinghaus, Miinster- 

 berg, Kibot, Pierre Janet, and by many contributions to 

 German, French, Italian, English, and American journals. 

 A useful summary of results is given by G. T. Ladd, 

 Element* of Physiological Psychology (1887). Founded 

 largely upon these is the brilliant work of W. James, 

 PrintipUt of Psychology ( 1890 ). Important text-books 

 re Sully's Outlines of Psychology ( 1884 ) and The Human 

 Mind (1892), Baldwin's Handbook of Psychology : Senses 

 and Intellect (2d ed. 1890) and his Elements (1893), 

 Dewey's Psychology (1889), J. C. Murray's Handbook of 

 Psychology (1885), Hoffding's 0utftneto/7V//<-Ao/>x/v(Kng. 

 trans. 1891 ), and Maher's Psychology ( R. Catholic, 1890). 

 Wundt's Lectvres on Animal atul Human Psychology 

 were translated in 1894 : C. Lloyd Morgan has published 

 An Introduction to Comparative Psychology (1894) and 

 Psychology for Teachers (1893); and (i. T. Ladd a 

 Primer of Psychology (1894). See also PHILOSOPHY, and 

 other articles cited there. 



Psychrometer, an instrument for measuring 

 the tension of aqueous vapour in the atmosphere : 

 a wet and dry bulb Hygrometer (q. v.). 



Ptah. See EGYPT, Vol. IV. p. 234. 



I'l.'irill i^.'lll (LoffOpui), a genus nearly allied 

 to the true Grouse (q.v.), differing chiefly in having 

 the toes as well as the legs thickly clothed with 

 short feathers. Hence the name Lagopus, a name 

 IIMM! by Pliny, from the resemblance of the foot to 

 that of a hare. The species are natives of the 

 northern parts of the world, of elevated or of arctic 

 region*. With the exception of the 'Red Grouse' 

 ( /,. xr.oticii.1 ), the species change colour on the 

 approach of winter, assuming a white or nearly 

 white plumage. All are esteemed as food. The 

 Ciiiiiinon Ptarmigan (L. mutiis) occurs in a few 

 parts of Scotland, but not in England or Ireland. 

 It U resident in the Lofoden Islands, in Scandi- 

 navia, on the Ural and the Altai ranges, &c., and 

 occurs on the Alps and the Pyrenees. The winter- 

 plumage is pure white, except a black hand almve 

 the eyes of the male, and some black on the under 

 feathers of the tail. In both sexes the wings are 



always white, but have dark shafts to their quills. 

 In summer the males are predominantly grayish 

 brown above, with blackish head, shoulders, and 

 breast, with white belly, with black tail-feathers 

 tipped with white. In the females a tawny colour 



Common Ptarmigan ( Lagopus unit UK ), summer and 

 winter plumage. 



predominates. In autumn, again, the plumage is 

 different, with numerous streaks of slate-gray on 

 the upper parts. The white winter-plumage is 

 doubtless protective amid the snow, and may be 

 the result of the cold ; the summer-plumage is not 

 less harmonious with the surroundings. It seems 

 that some moulting is associated with each of the 

 changes, but precise observations are wanting. A 

 rough nest is scraped in the ground ; the eggs ( eight 

 to ten ) are laid in May, and have a buff colour. Ptar- 

 migans are monogamous, but sometimes gregarious. 

 They feed on tender shoofe and berries. Among 

 the related species are the following : L. rupestris 

 (Siberia, Arctic America, &c. ), L. scoticus, or Red 

 Grouse, L. leitcurus (Rocky Mountains), L. hemi- 

 leucunts ( Spitzbergen ), and L. albus, or Willow- 

 grouse (in both hemispheres). Most of the 'ptar- 

 migan ' sold in British markets are willow-grouse. 

 See GROUSE, and Howard Saunders, British Birds. 



Pteria. See BOGHAZ-KEUI. 



Pterichthys (Gr., 'wing-fish'), a genus of 

 extinct Ganoid fishes, remains of which occur in 

 Devonian strata. The head and body were covered 



Pterichthys. 



with bony sculptured plates, and the pectoral fins 

 (to the wing-uke appearance of which the name 

 refers) were large and prominent. 



Pterocles, or PTEROCLETES. See SAND-GROUSE. 



Pterodactyl (Gr., 'wing-finger'), a remark- 

 able winged reptile, the remains of which are met 



