=Illustrative Method Involves Imagination.=--In the illustrative method, however, the pupil, instead of being able to apply directly former knowledge obtained through the senses, in interpreting the actual object, must make use of his imagination to bridge over the gulf between the actual object and the representation. When, for example, the child is called upon to form his conception of the earth with its two hemispheres through its representation on a globe, the knowledge will become adequate only as the child's imagination is able to picture in his mind the actual object out of his own experience of land, water, form, and space, in harmony with the mere suggestions offered by the model. It is evident, for the above reason, that the illustrative method often demands more from the pupil than does the more concrete objective method. For instance, the child who is able to see an actual mountain, lake, canal, etc., is far more likely to obtain an accurate idea of these, than the student who learns them by means of illustrations. The cause for this lies mainly in the failure of the child to form a perfect image of the real object through the exercise of his imagination. In fact it sometimes happens that he makes very little use of his imagination, his mental picture of the real object differing little from the model placed before him. The writer was informed of a case in which a teacher endeavoured to give some young pupils a knowledge of the earth by means of a large school globe. When later the children were questioned thereon, it was discovered that their earth corresponded in almost every particular with the large globe in the school. The successful use of the illustrative method, therefore, demands from the teacher a careful test by the question and answer method, to see that the learner has properly bridged over, through his imagination, the gulf separating the actual object from its illustration. For this reason an acquaintance with the mental process of imagination is of great value to the teacher. The leading facts connected with this process will be set forth in Chapter XXVII. PRECAUTIONS IN USE OF MATERIALS In the use of objective and illustrative materials the following precautions are advisable: 1. Their use in the lesson should not be continued too long. It should be remembered that their office is illustrative, and the aim of the teacher should be to have the pupils think in the abstract as soon as possible. To make pupils constantly dependent on the concrete is to make their thinking weak.