Written as Andrew North one or more chapters are available in a spoken word format.
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.
Works published in 1956 would have had to renew their copyright in either 1983 or 1984, 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 1985.