[Note: The term used nowadays in English is "SLENDER" rather than "SMALL" - CPD]
They have a long and a short sound. The long-sound vowels have a duration mark over them; the short-sound vowels have no such mark, thus:-
Two and three vowels coming together, with the sound of the one passing into the other, are called Diphthongs and Triphthongs; as, uan, uaigh.
Some have but one simple sound; as, gaol, ceum.
H is called the aspirate letter, and when used after the consonants b, p, f, m, c, g, d, t, s, it forms the aspirates, bh, ph, fh, mh, ch, gh, dh, th, sh.
[Note: The term used nowadays in English is "lenition". The term traditionally "aspiration", although traditionally used in English grammars of Gaelic, is actually phonetically incorrect. - CPD]
When used at the beginning of a word it is written thus, h-; as na h-uain; and has a strong breathing sound.
The letters, sg, sm, sp, st, have no aspirated form.