Through time and tempo also, poetic rhythm is expressive, much after the manner of music; by these means too, in addition to the mode of stress-undulation, it imitates the temporal and dynamic course of action and emotion, and so tends to arouse congruous types of feeling in the mind; it is swift or slow, gliding or abrupt, retarded or accelerated. Compare the slow and retarded rhythm of "When I have fears that I may cease to be," so well adapted to express the gravity of the thought, with the rapid and accelerated movement of "Hail to thee, blithe spirit!" so full of a quick joyousness. Or compare the light legato movement of "Bird of the wilderness, blithesome and cumberless," with the heavy staccato movement of "Waste endless and boundless and flowerless." Yet, for all its expressiveness, the music of verse can never stand alone. It is too bare and tenuous by itself to win and keep the attention or to evoke much feeling. It does not possess the purity of color, the loudness, force, or volume of sound that belong to music and make music, almost alone of the arts, capable of existing as mere form. The rhythm of poetry, derived very largely from a rhythm of thought, has need of thought for significance. The thought and the music are one. For this reason poetry is better, I think, when read to oneself than when read aloud; for then the sound and the sense are more intimate; the attention is not drawn off to the former away from the latter. Moreover, try as he will, the poet can never make his word-sounds fully harmonious; some roughness and dissonance will remain; but in silent reading these qualities disappear. However, although by itself of small significance, the musical element in verse makes all the difference between poetry and prose. Through its own vague expressiveness it fortifies the emotional meaning of the poetic language, and, at the same time, sublimates it by scattering it in the medium. And finally it imparts an intimacy, a personal flavor, which also allies poetry with music; for the substance of rhythm is the movement of our own inner processes; the rhythm of thoughts and sounds is a rhythm in our own listening and attending, our own thinking and feeling; the emotional values spring from us as well as from the subject-matter. Hence even narrative and dramatic poetry have a lyrical tone; we ourselves are implicated in the actions and events portrayed.