Thanks for the info on Derry, DK. There's another, even more significant discussion by Brian Audley called "The Provenance of the Londonderry Air," published in the Journal of the Royal Musical Association in 2000.

Audley finds that

1. there's no record of a tune that is *clearly* the "Londonderry Air" before it was noted by Jane Ross in 1854,

2. but the shape of the air relates it to earlier melodies such as "Castle Hyde" and "The Young Man's Dream" (though only the latter bears any readily audible resemblance to it - and even that isn't clearly "the same"); so there's no doubt that the "Air" has traditional roots, no matter who adapted it.

Michael Robinson has posted Irish words (of 1831 or earlier) to "The Young Man's Dream":

http://www.standingstones.com/aisling.html

There seem to have been several English translations.

3. Very interestingly, Sam Henry collected a tune that *is* an obvious (if less polished) variant of the "Londonderry Air" from the itinerant whistle-player Simon O'Doherty of Co. Antrim in 1934. O'Doherty claimed to have learned the tune from his grandfather, who had been a noted piper in Donegal. O'Doherty called it "The Riverside," which he said was the name of a song (which he'd unfortunately forgotten) sung by his mother.

Audley observes that the 18th century song in English, "The Young Man's Dream," was set "by a murm'ring river's side." Edward Bunting collected several versions, and published the one played by the harper Dennis Hempson of Magilligan, Co. Derry in 1792. None is as graceful as the "Air," however.