According to WIKIPEDIA Danny Boy was initially written to a tune other than "Londonderry Air".The words to "Danny Boy" were penned by English lawyer and lyricist Frederic Weatherly in Bath,Somerset in 1910. After his Irish-born sister-in-law Margaret (known as Jess) in the UnitedStates sent him a copy of "Londonderry Air" in 1913, Weatherly modified the lyrics of "Danny Boy"to fit the rhyme and meter of "Londonderry Air".
Weatherly gave the song to the vocalist Elsie Griffin, who made it one of the most popular songsin the new century; and, in 1915, Ernestine Schumann-Heink produced the first recording of "Danny Boy".
Jane Ross of Limavady is credited with collecting the melody of "Londonderry Air" in the mid-19thcentury from a musician she encountered.