The end of the "intellectual machine"

The three fan letters Cowper received didn't cure his mental health problems. "The experiment for the restoration of his Mind," Hayley wrote, "did not certainly succeed to the extent of my Wishes, & my Expectations."

However, in Hayley's opinion, there was "great reason to believe, that the unexpected Letters, which He actually received, made a beneficial Impression on his Spirits; & gave a wonderful activity to his Mind, even while it seemed to be involved in impenetrable Gloom."

Around this time, after months of inactivity, Cowper resumed work on his long-neglected translations of the Iliad and the Odyssey. This could, of course,  have been coincidence, but Hayley attributed it firmly to his own intervention:

the Revival & Improvement of [Cowper's] Homer, while his Spirits appeared for unfit for such a Task, may be regarded as one of the most marvellous Facts, that can be discovered in the History of the human Mind.

Cowper continued to work and when, on 31 January 1800, Hayley received a letter from Johnny Johnson, enclosing a short, newly translated passage from the Iliad, in Cowper's handwriting, he was ecstatic.

[I]t appeared to me as a blessed omen of his being entirely Himself again - The Emotions of my Heart upon that Idea immediately gave rise to the following …
Sonnet

Blest be the Characters so Kindly trac’d
In that dear Hand which I have longed to view
Pledge of Affection old and Kindness new
From the reviving Bard supremely graced
With all the Gifts of Fancy and of Taste
That can Endear the Mind! and given to Few
The rarer richer Gift, a Heart as true
As e’er the Arms of Amity embraced.

Ecstatic Tears I on the Paper shed
That speaks, my Cowper! of thy mental Health
And of thy Friendship, soothing as the Dove!
So weeps the Nymph, who, when long Storms are past
Welcomes from the Sea her Bosom’s rescued Wealth
To Life to Joy to Glory and to Love

It's hardly great poetry. But the last three lines are interesting. They seem, like a magic mirro,r to reflect a happy ending onto the final stanza of Cowper's last, original poem, "The Cast-away" (written March 1799 and first published in Hayley's biography of his friend):

No voice divine the storm allay'd,
   No light propitious shone;
When, snatch'd from all effectual aid,
   We perish'd, each alone:
But I beneath a rougher sea,
And whelm'd in deeper gulphs than he.

This is somewhat uncanny, as it's almost certain that Hayley didn't see the poem until January 1801.
A couple of weeks after Hayley received the letter that so fed his optimism, Cowper fell ill. A couple of months later, he was dead.