Vowels are five, a, e, i, o, u.

Such is the number generally received; but for i it is the practice to
write y in the end of words, as thy, holy; before i, as from die, dying;
from beautify, beautifying; in the words says, days, eyes; and in words
derived from the Greek, and written originally with υ, as sympathy,
συμπαθεια, system, συστημα.

For u we often write w after a vowel, to make a diphthong; as, raw, grew,
view, vow, flowing; lowness.

The sounds of all the letters are various.

In treating on the letters, I shall not, like some other grammarians,
inquire into the original of their form, as an antiquarian; nor into
their formation and prolation by the organs of speech, as a mechanick,
anatomist, or physiologist; nor into the properties and gradation of
sounds, or the elegance or harshness of particular combinations, as a
writer of universal and transcendental grammar. I consider the English
alphabet only as it is English; and even in this narrow disquisition I
follow the example of former grammarians, perhaps with more reverence
than judgment, because by writing in English I suppose my reader
already acquainted with the English language, and consequently able to
pronounce the letters of which I teach the pronunciation; and because
of sounds in general it may be observed, that words are unable to
describe them. An account, therefore, of the primitive and simple
letters, is useless, almost alike to those who know their sound, and
those who know it not.

OF VOWELS