186 THE DISCOVERY OF THE CHILD To the tones are added the semi-tones, which, to prevent waste of energy, are recognizable by the bell-stands, which are black instead of white (recalling the keys of the pianoforte). The exer- cise consists in placing the semi-tones in connection with the respective tones.1 One must not confuse the sense-education of the musical sense in general technique, which delimits it, with musical education. One may carry out the exercises in identifying tones without entering at all into the field of music, just as, in another field, the scientific, they make studies in physics, which are concerned with the vibrations of matter including that special form which produces musical notes. The sense-exercise represents the essential base for musical education. The child who has done such exercises is extremely well prepared for listening to music, and therefore for making more rapid progress. It is not necessary' to say that, for this very reason, music itself will continue and strengthen the sense education, just as the study of painting will continue the study of colours, etc. The exact base of a " classified perception " which is fixed within the child like a foundation stone for comparison, possesses an inestim- able initial value for continued progress. 1 It was in the course of these exercises with the bells that notice was iafcen of the maximum number of repetitions of the same exercise in a single round; there were counted as many as 200 repetitions by children between six and seven years of age.