Excerpt from "OF VOWELS: "A.
A has three sounds, the slender, open, and broad.
A slender is found in most words, as face, mane, and in words ending in ation, as creation, salvation, generation.

The a slender is the proper English a, called very justly by Erpenius, in his Arabick Grammar, a Anglicum cum e mistum, as having a middle sound between the open a and the e. The French have a similar sound in the word pais, and in their e masculine.

A open is the a of the Italian, or nearly resembles it; as father, rather, congratulate, fancy, glass.

A broad resembles the a of the German; as all, wall, call.

Many words pronounced with a broad were anciently written with au; as sault, mault; and we still say, fault, vault. This was probably the Saxon sound, for it is yet retained in the northern dialects, and in the rustick pronunciation; as maun for man, haund for hand.

The short a approaches to the a open, as grass.

The long a, if prolonged by e at the end of the word, is always slender, as graze, fame.

[18] A forms a diphthong only with i or y, and u or w. Ai or ay, as in plain, wain, gay, clay, has only the sound of the long and slender a, and differs not in the pronunciation from plane, wane.

Au or aw has the sound of the German a, as raw, naughty.

Ae is sometimes found in Latin words not completely naturalized or assimilated, but is no English diphthong; and is more properly expressed by single e, as Cesar, Eneas.