Whitsun is celebrated about 7 weeks after Easter, so it's also a moveable feast. I would say Whitsun is mainly associated with June. But this year it falls in May. So for now we can consider songs like the Whitsun Carol and Dancing at Whitson (both in the Digital Tradition database) and Maidín Luan Cincise (a patriotic song in Irish Gaelic, "On Whit Monday Morning") at https://songsinirish.com/maidin-luain-chincise-lyrics/ but I'll put it in Mudcat later with translation and a bit of info. I don't know what date Whit Monday fell in 1798, however.