This division includes the use made of the qualities of sound for the purpose of adding to the melodiousness of verse, or of expressing in some measure the ideas to be conveyed by means of the very sounds employed. Sometimes this takes the form of alliteration, differing from that of early English verse only in that it follows no regular structural laws. On the other hand, it may take the form of _onomatopœia_, the figure of speech in which sound and sense are closely related,--as in descriptive words like _buzz_, _hiss_, _murmur_, _splash_, and the like. The term Tone-color is formed by analogy with the German _Klangfarbe_, an expression apparently due to the feeling that the sound-qualities of speech have somewhat the same function as the various colors in a picture. It is unquestionably true that the selection of sounds, whether vowel or consonantal, has much to do with the melodious effect of very much poetry. The poet may choose the different sound-qualities (so far as the sense permits) just as the musician may choose the varying qualities of the different instruments in the orchestra or the different stops in the organ. Strictly speaking, this matter of Tone-color is not a part of verse-form in the same sense as matters of rhythm, rime, and the like; for it may appear in prose as well as in verse, and is not in any case reducible to formal principles or laws. Yet its use in actual verse is so important, and it is so closely related to the use of sound-quality in the form of rime and alliteration, that it seems well to include it here.[15]