Note c — BOOK IV.

Because it would be endless to specify the curious Mechanism of all the Parts, concurring to the Formation of the Voice; I shall therefore for a Sample note only two Things, 1. There are thirteen Muscles provided for the Motion of the five Cartilages of the Larynx, Gibs. Anat. l. 2. c. 14, a Sign of the careful and elaborate Provision that is made for the Voice. 2. It is a prodigious Faculty of the Glottis, in contracting and dilating itself with such Exquisiteness, as to form all Notes. For (as the ingenious Dr. Keil saith) supposing the greatest Distance of the two Sides of the Glottis, to be one tenth Part of an Inch in sounding 12 Notes, (to which the Voice easily reaches;) this Line must be divided into 12 Parts, each of which gives the Aperture requisite for such a Note, with a certain Strength. But if we consider the Sub-division of Notes, into which the Voice can run, the Motion of the Sides of the Glottis is still vastly nicer. For if two Chords sounding exactly Unisons, one be shortened, ⅟₂₀₀₀ Part of its Length, a just Ear will perceive the Disagreement, and a good Voice will sound the Difference, which is ⅟₁₉₆ Part of a Note. But suppose the Voice can divide a Note into 100 Parts, it follows that the different Apertures of the Glottis actually divide the tenth Part of an Inch into 1200 Parts, the Effect of each of which produces a sensible Alteration upon a good Ear. But because each Side of the Glottis moves just equally, therefore the Divisions are just double, or the Sides of the Glottis, by their Motion do actually divide one tenth Part of an Inch into 2400 Parts. Keil’s Anat. c. 3. Sect. 7.