Poet of Nature, thou hast wept to know
That things depart which never may return:
Childhood and youth, friendship and love's first glow,
Have fled like sweet dreams, leaving thee to mourn.
These common woes I feel. One loss is mine
Which thou too feel'st, yet I alone deplore.
Thou wert as a lone star, whose light did shine
On some frail bark in winter's midnight roar:
Thou hast like to a rock-built refuge stood
Above the blind and battling multitude:
In honored poverty thy voice did weave
Songs consecrate to truth and liberty,--
Deserting these, thou leavest me to grieve,
Thus having been, that thou shouldst cease to be.
London, 1802
William Wordsworth
Milton! thou should'st be living at this hour:
In these final two lines, Shelley transforms Wordsworth himself into one of the fleeting “things” that Wordsworth had earlier lamented–this kind of recapitulation is typical of Shelley’s poetics. See for instance,  To Edward Williams : 
 Of hatred I am proud,—with scorn content; Indifference, that once hurt me, now is grown Itself indifferent;
To Wordsworth