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 1926 would have had to renew their copyright in either 1953 or 1954, i.e. at least 27 years after it was first published / registered but not later than in the 28th year. As it was not renewed, it entered the public domain on 1 January 1955.
The author died in 1955, so this work is also in the public domain in countries and areas where the copyright term is the author's life plus 60 years or less. This work may also be in the public domain in countries and areas with longer native copyright terms that apply the rule of the shorter term to foreign works.