This work is in the public domain in the United States because it was legally published within the United States (or the United Nations Headquarters in New York subject to Section 7 of the United States Headquarters Agreement) before 1964, and copyright was not renewed.
- For Class A renewals records (books only) published between 1923 and 1963, check the Stanford University Copyright Renewal Database.
- For other renewal records of publications between 1922–1950 see the University of Pennsylvania copyright records scans.
- For all records since 1978, search the U.S. Copyright Office records.
Works published in 1961 would have had to renew their copyright in either 1988 or 1989, i.e. at least 27 years after it was first published / registered but not later than 31 December in the 28th year. As it was not renewed, it entered the public domain on 1 January 1990 .