Foot in Bacchius

A trisyllable foot consisting of a short vowel followed by two long vowels in quantitative meter or an unstressed syllable followed by two stressed syllables in qualitative meter found in English verse is called the Bacchius as shown in the table below.

It is a rare metrical foot found in poetry but here are examples of its use found
in this poem:

Keats “Ode to a Nightingale” Stanza 1, verses 1-6 as scanned below:

My heart aches, and a drowsy numbness pains
    My sense, as though of hemlock I had drunk,
Or emptied some dull opiate to the drains
    One minute past, and Lethe-wards had sunk:
'Tis not through envy of thy happy lot,
    But being too happy in thine happiness, -