Very Interesting! Philippa your Gaelic text is the same as the one I know, The English tune to "I will go, I will go" is close to the Gaelic, but not the same. The Gaelic song was telling about the Gaels fighting the French in Holland (1799) Thus the Kings Son would be one of the Hanovarian Princes. (An interesting fact being that the dispora of Gaels in Virgina and Carolina fought for the Hanovarian Crown durring the American War of Independence. It is something in the Gaelic nature to follow any King, once they have proved they are fit to rule, even if they have caused you some problems.) The author? As far as I can tell its a man called "Leodach" and you don't need to speak the Gaelic to figur out that just means a MacLeod!

Slan leat

Aodh.