Interestingly, this song has been mentioned on the Eldred v. Ashcroft bulletin board in a discussion of the usefulness of the public domain. The post is here (login "guest", password "guest"). The note cites to an article, "Getting Kathleen Home Again", by Richard S. Hill, in Notes, Second Series, Volume 5, Number 3, June, 1948, page338. Hill's article, according to the BBS post, states that "Kathleen" went into the public domain in 1932, and that "by 1947 forty arrangements had been registered by twenty-seven publishers". It also provides the following links to the Library of Congress web site:

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