With a great literature in the form of special studies, we must yet, on the whole, admit that we possess no general formula in the philosophy or psychology of music which covers the whole ground. Schopenhauer has said that music is the objectification of the will--not a copy or a picture of it, but the will itself; a doctrine which however illuminating when it is modified in various ways is obviously no explanation of our experience. Hanslick has but shown what music is not; Edmund Gurney's eloquent book, "The Power of Sound," is completely agnostic in its conclusion that music is a unique, indefinable, indescribable phenomenon, which possesses, indeed, certain analogues with other physical and psychical facts, but is coextensive with none. Spencer's theory of music as glorified speech is not only in a yet unexplained conflict with many facts, but has never been formulated so that it could apply to concrete cases. The same is true of Wagner's "music as the utterance of feeling." But there is a body of scientific facts respecting the elements of music, in which we may well seek for clues. As facts alone they are of no value. They must be explained as completely as possible; and it is probable that if we are able to reach the ultimate nature and origin of these elements of music they will prove significant, and a way will be opened to a theory of the whole musical experience. The need of such intensive understanding must excuse the more or less technical discussions in the following pages, without which no firm foundation for a theory of music could be attained. II The two great factors of music are rhythm and tone-sensation, of which rhythm appears to be the more fundamental. Rhythm is defined in general as a repeating series of time intervals. Events which occur in such a series are said to have rhythm. In aesthetics, it is the periodic recurrence of stress, emphasis, or accent in the movements of dancing, the sounds of music, the language of poetry. Subjectively it is the quality of stimulation due to a succession of impressions (tactual and auditory are most favorable) which vary regularly in objective intensity. We desire to understand the nature, and the source of the pleasing quality, of this phenomenon.