PSYCHOLOGY 



4861 



PTERODACTYL 



in work of recent date. The mind is consid- 

 ered as a unit, with the power of acting in vari- 

 ous ways to secure specific results. Instead of 

 a faculty of memory, for example, the mind 

 acts to recall past experiences, and in connec- 

 tion with this special form of activity other ac- 

 tivities may be present, as feeling and will, but 

 so long as the person is trying to recall past ex- 

 periences the form of activity which we call 

 memory will be the strongest. This is equally 

 true of other forms of activity. When we speak 

 of will, we mean that activity of the mind 

 which enables us to choose and to act. When 

 we speak of feeling, we mean the activity 

 through which we experience pleasure or pain. 



Development of Mental Powers. Modern 

 psychology recognizes the fact that the various 

 forms of mental activity develop in accordance 

 with a fixed law, and that the order of their de- 

 velopment never varies. This order is (1) ob- 

 servation, (2) memory, (3) imagination, (4) 

 thought, which includes conception, judgment 

 and reason,. Feeling and will are present at 

 birth, and with the other activities increase in 

 strength as the mind develops. A knowledge 

 of these facts is of great importance to the 

 teacher who without such knowledge might set 

 tasks for children which they do not have the 

 mental capacity to perform. 



Classification. Psychology is classified in 

 various ways by different authorities, but these 

 classifications are of interest to special students 

 only. We have already mentioned physiological 

 psychology. Child psychology is devoted to 

 the study of the mental development of chil- 

 dren, and is generally known as child study. 

 Educational psychology treats of the applica- 

 tion of the laws of mental development to 

 teaching. W.F.B. 



Consult Tlchener's Beginner's Psychology; 

 Baker's Elementary Psychology; Watson's Be- 

 havior. 



Hrlatrd Subject*. The reader is referred for 

 further treatment of this subject to the articles 

 on the following: topics : 



The articles on the following psychologists may 

 also be consulted: 



Dewey, John 

 Galton, Sir Francis 

 Hall, G. Stanley 



Apperception 



Association, LAW of 



Attention 



Brain 



Child 



Child Study 



Concept 



Dreams 



Peeling; 



Froe Will 



Habit 



rlnation 

 Imagination 



Instinct 



Interest 



Judgment 



Memory 



Mind 



Pedagogy 



Perception 



Reason 



Senses, Special 



Suggestion 



Thought 



Will 



Helmholtz, Hermann von 

 James, William 

 Mtinsterberg, Hugo 



THE PTARMIGAN 

 About one-tenth actual size. 



PTARMIGAN, tahr'migan, a group of birds 

 of the grouse family, found in northern regions 

 of both continents. A characteristic feature of 

 these birds is a covering of short feathers on 

 the feet. Most species have several changes of 

 plumage during 

 the year; the 

 winter coat is a 

 pure white and 

 that of summer a 

 mixture of red- 

 dish-brown, buff, 

 gray and black, 

 the coloration 

 serving at differ- 

 ent seasons to 

 protect the bird 

 from discovery 

 by its enemies. 

 Ptarmigans nest among mosses on the ground. 

 Their eggs, six to eleven in number, vary in 

 color from cream-buff to reddish, and are spot- 

 ted and blotched with black or dark brown. 



PTERIDOPHYTES, tcr' i doh files, from two 

 Greek words meaning fern and plant, is the 

 name given to that division of the plant king- 

 dom which includes ferns, club mosses and 

 horsetails, or scouring rushes. It is one of the 

 four grand divisions into which plants are di- 

 vided (see in these volumes the article BOTANY, 

 pages 861 and 862). These plants have real 

 roots, but no stem, although the rootstock 

 often resembles one. Many of them are trop- 

 ical, and in the geological period, particularly 

 in the earth's greatest coal-forming ages, they 

 were far more abundant than they are now. 

 See FERNS; GEOLOGY. 



PTERODACTYL, tcr o dak' til, an order of 

 flying lizards that lived in prehistoric times. 

 Numerous fossil remains found in limestone 

 formations of the Mesozoic Age indicate that 

 there were about twenty genera of these oddly- 

 formed creatures. They had hollow bones, 

 like birds, but in other points of structure were 

 like reptiles. The body was short, the head 

 large, and there were two long, slender hind- 

 legs and a pair of forclimbs. A very long tail 

 was characteristic of earlier forms. Probably 

 the most peculiar point of structure was the 

 prolongation of the fifth finger of the fore- 

 limb. To this was attached a strong mem- 



