But, advancing a further step from the particular consideration of science as the knowledge of forms, let us come to the fact that as all art is a congeries of forms, each art must have its own peculiar science; and always we have, in a true sense, the art of an art and the science of that art. For example, correlative to the art of music, we have the general science of music, which indeed consists of several quite separate sciences. If a man desire to become a musical composer, he is absolutely obliged to learn (1) the science of Musical Form, (2) the science of Harmony, and (3) the science of Orchestration or Instrumentation. The science of musical form, concerns this sort of matter, for instance. A symphony has generally four great divisions, called movements, separated usually from each other by a considerable pause. Each of these movements has a law of formation: it consists of two main subjects, or melodies, and a modulation-part. The sequence of these subjects, the method of varying them by causing now one and now another of the instruments to come forward and play the subject in hand while subordinate parts are assigned to the others, the interplay of the two subjects in the modulation-part,--all this is the subject-matter of a science which every composer must laboriously learn. But again: he must learn the great science of harmony, and of that wonderful tonality which has caused our music to be practically a different art from what preceding ages called music; this science of harmony having its own body of classifications and formulated laws just as the science of Geology has, and a voluminous literature of its own. Again, he must painfully learn the range and capacities of each orchestral instrument, lest he write passages for the violin which no violin can play, &c., and further, the particular ideas which seem to associate themselves with the tone-color of each instrument, as the idea of women's voices with the clarionet, the idea of tenderness and childlikeness with the oboe, &c. This is not all; the musical composer may indeed write a symphony if he has these three sciences of music well in hand; but a fourth science of music, namely, the physics of music, or musical acoustics, has now grown to such an extent that every composer will find himself lame without a knowledge of it.