From Lomax's book, Cowboy Songs & Other Frontier Ballads, first copyrighted in 1910:
This must have been a very popular song throughout the middle of the nineteenth century, for its melody was used for no fewer than four political songs between 1840 and 1875. The origin of "Old Rosin" is not clear, but it must have been English or Scottish or Irish, and it probably dates from the opening of the century.
Curiously enough, the name of the hero was generally given as "Rosin, the Bow", and it is quite possible that this was considered a descriptive title for a fiddler or some other type of minstel. But the authentic spelling is unquestionably "Beau", and there is still nothing to prove that old Rosin was anything more than popular ladies' man with alcoholic tendencies.