What are some of the "sound devices" used in "Elegy Written in a Country Churchyard" by Thomas Gray?

In his famous "Elegy Written in a Country Churchyard,"
Thomas Gray uses several forms of poetic "sound devices."  Here are some
examples.

1. Alliteration: The
repetition of initial consonant sounds.

Line 2: "The
lowing herd wind slowly o'er the
lea"

Line 4: "The
plowman homeward plods his
weary
way"

Line 28: "How
bow'd the woods beneath their
sturdy
stroke"

2.
Rhyme:

In most places, Gray
uses standard, "full" rhyme: day-lea, sight-flight, holds-folds, complain, reign,
etc.

Occasionally, though, Gray uses partial
rhymes.

Lines 29,31: toil,
smile

Lines 30, 32: obscure,
poor

Lines 58, 60: withstood,
blood

Some of these may indicate that Gray's pronunciation
was different than our contemporary pronunciation.  In other cases , he may simply be
"stretching" his rhymes.

Onomatopoeia:
words that imitate a sound (moo, meow,
etc.)

I have not been able to find examples of onomatopoeia
in Gray's "Elegy."  At first, I thought that the words "tolls," "knell," and "lowing,"
might be onomatopoeic, but the dictionaries I consulted do not seem to agree with this
theory.