Jim, Graves's words as given in his own "Father O'Flynn and Other Irish Lyrics" are quite different from Crehan's, which are unfamiliar to me. Thanks for posting them.

Here is Russell's English translation of the Irish. It seems unrelated to Graves's song (and is even less to my taste!):

O fair is the hour when on leaf and flower
The sparkling dew drops all brightly shine,
E'er the white sun's blaze and his dazzling rays
Of the morning mist leave scarce a sign.
All changeless and still over valley and rill
Lies the Foggy Dew of the Autumn night,
With its grey-blue sheen on the pastures green,
That's fairer far than the sun beams bright.

All the flowery vales and the bosky dales,
Untouched by the unborn morning breeze,
Are filled to the brim with a vapour dim,
And seem from afar like inland seas.
O that witching time e'er the sun in his prime
Drinks the sparkling dew from each glossy stem, —
Ere the full blown day drives the mist away
That makes of each drooping leaf a gem !

My guess is that the Irish words were inspired by the title of the tune, which, if I read the sources rightly, was - for trained musicians and others - usually that given by Bunting and employed by Graves.

The tune that is better known today, to which Canon O'Neill wrote the Easter Rising lyrics, seems first to have appeared in 1909, collected from Cathal McGarvey, the same man, presumably, who penned the lyrics of "The Star of the County Down."

It certainly seems unlikely (to put it mildly) that an English printer and an Irish musician should have come up independently with a title including the phrase "Foggy Dew."

And indeed, Joyce's 1909 version, learned "as a child" and somewhat like Bunting's is accompanied by one chastened stanza of "The Foggy, Foggy Dew."