Ei.
The sound of ei is either made up of the sounds of both the vowels, or like that of e alone.
1. Made up of (1) e and (1) i: e long, i short, as, sgeimh beauty; e short, as, meidh a balance.
2. Made up of (2) e and (1) i: e long, i short, as, feidh deer; e short, as, greigh a herd, stud.
Before a Lingual or a Palatal, not quiescent, the i loses its sound, and only qualifies that of the following consonant; hence,
3. Like (1) e alone: long, as, mèise of a plate.
4. Like (2) e alone: long, as, éigin necessity; short, as, eich horses.