Source: Philip Carolan Manuscripts [1:66]¹. More information on the manuscripts here.

Another version of this tune from the same collection can be found here, which displays similarities in contour to the a-part while having an altogether different b-part.

1. Angela Buckley, A Critical Edition of The Irish Music Manuscripts of Philip Carolan (c1839-1910). Masters thesis, Waterford Institute of Technology, 2007, Vol.2 p23.