Things principally requisite to the Voice, are, that the Wind-pipe, the former thereof be solid, dry, and of the nature of Resounding Bodies.  By this Hypothesis, two of the most Eminent Phaenomena’s of the Voice are discovered; why the Voice should then at length become firm and ripe, when the Bones have attained unto their full Strength, and due Hardness, which cometh to pass much about the Years of ripe age, when the vital Heat, doth in a greater degree exert itself:  The other Phaenomenon is Hoarsness or an utter loss of the Voice, which is, when the Cartilages, or Gristles of the Throat, especially the Epiglott, or Coverlid of the Wind-pipe, is lined or besmeared all over with a slimy Viscosity, whereby they lose their Elasticity, or Springiness.  Now these Symptoms of the Voice are also common to other Wind-instruments, when they become too much moistned by any vapourous wetting Air.  The same reason also is to be assigned why the Voice doth at last quite cease in those who have made too long Harrangues, in speaking, and whose Jaws are quite dried with an immoderate Heat; for in both these cases the top of the Wind-pipe is covered over with a clammy Tenacious Phlegm.

There remains yet two other Symptoms of the Voice, which I have undertaken to explicate, viz. why the Voice sometimes leaps from one Eighth to another; and, as it is rightly said by the Vulgar Expression, that it is broken:  and why, when we strive to make our Voice either too sharp, or too flat, it at last plainly faileth us.  As to the first, let us consider when and how it cometh to pass; and first, it’s what principally happeneth to Orators, when they endeavour to lift up their Voice too high, or strongly; but how this cometh to be, Organ-pipes, and the Monochorde, do teach us, viz. when some Impediment interposing, doth divide the ordinary Sound into two; if therefore those parts are equal, either of them is by one Eighth more sharp than the former Sound, neither are they distinguished from one another; but if they prove to be unequally divided, then two distinct Sounds are made at the same time, whereof one is flatter than the ether, and this is commonly called a broken Voice:  But why our Voice should fail us, when we endeavour to make it more sharp, or more flat than it ought to be, the reason is, because we strive either so to contract the Cleft of the Wind-pipe, and to press the Spout-like Cartilage, by help of the Bone of Tongue, towards the Epiglott, that the going forth of the Voice, and of the Breath, may be precluded, or else, on the contrary, because that the said Cleft, through the drawing down of the Cartilages, is so much widened, that the departing out of the Breath, finds no hinderance.