Thanks for the link Jerry:

Pádraig Mac Niocaill: Pe´arla an Bhrollaigh Bha´in

It's a lovely tune. I have the music in a book called Soodlum's Irish Ballad Book

The note on that page says, "The tune, translation and text, is to be found in the Collection of George Petrie (1855) who founded the Society for the Preservation and Publication of the melodies of Ireland. He lived at 67 Lr Rathmines Road, Dublin."

I