Analysis of Sonnet -Written in Keats

I saw pale Dian, sitting by the brink
Of silver falls, the overflow of fountains
From cloudy steeps; and I grew sad to think
Endymion's foot was silent on those mountains.
And he but a hush'd name, that Silence keeps
In dear remembrance,—lonely, and forlorn,
Singing it to herself until she weeps
Tears, that perchance still glisten in the morn:—
And as I mused, in dull imaginings,
There came a flash of garments, and I knew
The awful Muse by her harmonious wings
Charming the air to music as she flew—
Anon there rose an echo through the vale
Gave back Enydmion in a dreamlike tale.