But the _æsthetics_ of vocal art, and the spiritual inspiration of the form (of the sound), comprise the whole domain of music and poetic beauty. [1] Those who are interested in the history of music are referred to the historical works already mentioned for a fuller account of what is only alluded to above. II PHYSIOLOGICAL VIEW FORMATION OF SOUND BY THE ORGAN OF THE HUMAN VOICE The great physiologist, Johannes Müller, fastened a larynx, which he had cut out with the whole trachea belonging to it, to a board, and, stretching the vocal chords by a weight that could be increased or diminished at pleasure, caused vibrations in it by blowing through the trachea with a pair of bellows, or through a tube with his own breath. In this way he succeeded in producing almost all the tones of the human voice, and even some which are beyond the compass of this organ. He distinguished two different kinds of tones, to which he gave the names of the chest register and the falsetto register. The chest tones were produced when the vocal ligaments, slackly stretched, were made to vibrate easily in their whole breadth; the falsetto tones came merely through the vibration of the fine inner edges of the vocal chords when they were more tightly stretched. At a moderate stretching of the vocal chords, it depended upon the manner of blowing whether a sound corresponding to the chest voice or to the falsetto were produced, or whether it were higher or lower for several tones, often for a whole octave. A series of tones of more than two octaves could thus be produced in the same larynx, with, however, gaps and places at which the vocal chords, instead of being stretched gradually, have to be _stretched at once very strongly, in order that the succeeding higher half tone may be reached_. Such a place Müller indicates from c² to c♯², or d² to d♯², with the remark that it differs in different larynxes, being in some higher and in some lower. But in order to render practicable the proper stretching of the exsected larynx, muscles and membranes have to be cut, which sufficiently proves that the functions of the organ of singing in the living must be differently carried on. _Dr. Merkel_, in Leipzig, has continued these experiments, and by means of a peculiar contrivance has succeeded in producing all the tones in the exsected larynx, without mutilating it. But these investigations, interesting as they are, throw no certain light upon the formation of sound by the vocal organ in the living.