From Irish Folk Music by Francis O'Neill (Chicago: The Regan Printing House, 1910):

[There are] few born in Ireland who have not heard of the song named "Rocking the Cradle," or, as it is sometimes called, "Rocking a Baby that's None of My Own." Both song and air are now almost entirely forgotten, and it was a matter of no little difficulty to get a setting of the music. In preference to an unsatisfactory version of my own, we selected a setting found in an American publication of over fifty years ago. A fair version was also printed in Smith's Irish Minstrel, published in 1825 at Edinburgh.

It was quite a trick to play this piece to suit the old Irish standard of excellence, in which the baby's crying had to be imitated on the fiddle. To bring out the tones approaching human expression, the fiddle was lowered much below concert pitch. The performer held firmly between the teeth one end of a long old-fashioned door key with which at appropriate passages the fiddle bridge was touched. This contact of the key produced tones closely imitating a baby's wailing. Miss Ellen Kennedy, who learned the art from her father, a famous fiddler of Ballinamore, County Leitrim, was very expert in the execution of this difficult performance.