[VOWELS.]
[32]. Vowels are sounds which are produced by the vibrations of the vocal chords (this may be easily felt by placing a finger on the throat at the Adam’s apple) and without any audible friction or any obstruction anywhere in the passage above the vocal chords. The difference in the sound of the vowels is due to the different shape which the position of the tongue and the lips gives in each case to the cavity of the mouth. During the pronunciation of pure vowels no air escapes through the nose.
[33]. The simple vowels, a, e, i, o, u (y), are either long or short. The sound of a long vowel is considered to be twice the length of that of a short.
[34]. That a long vowel is equal to two shorts is a rule of metrical theory (see [2515]). In actual pronunciation, there were undoubtedly various degrees of length, as in English: e.g., sea, seize (long), cease (half-long).
[QUANTITY OF VOWELS.]
The quantity of vowels must in general be learned by observation; but some convenient helps for the memory may be found in [2429]; and the quantity of many vowels may be ascertained by the general principles given in [35] and [36]. Except in the case of Hidden Quantity ([2459]), the quantity of vowels is in general ascertained from verse. But some information may also be gleaned from such rhetorical prose as exhibits well defined habits in the rhythmical endings selected for sentences (clausulae, Cic. O. 191-226).
[35]. A vowel is short:
([1.]) Before another vowel or h ([124]): as, eōs, ēvehō; compare taceō with tacēre. For exceptions in classical Latin, see [127]; for exceptions in early Latin see [126].
([2.]) Before nt and nd ([128]) if not the result of contraction: as, calendae, centum; compare amant, amandus, with amāre.