Thank you for all this, Steve. Almost too much to handle. "Brian" must have been one of the most popular songs of 1800-1850. I've found many passing refs. in books and newspapers.

For example, from William Johnson Neale's "Cavendish" Vol. 1 (of 3), p. 67 (London: Henry Colburn and Richard Bentley, 1831):

“An old Irish sailor was sitting next me [in the foundering boat] who had been cracking his jokes on all around, and the first thing I heard amid the din of waters, was his gruff voice chaunting a snatch from the humorous ballad of Brien [sic] O'Linn; it was,

             The bridge tumbled down, and they all fell in,
             ‘Strike out and be d----d!’ cried Brien O’Linn.

These sailors are without parallel, joking and swearing in the very arms of death.”