When the ball dropped in Times Square on New Year's eve, George Gershwin's composition "Rhapsody in Blue," along with most other works that were first published in 1924, entered the public domain in the U.S. This is the second year in a row that the public domain in the U.S. has been enriched in this manner: last year (as recounted in this post), most works published in 1923 fell into the public domain. (As an aside, I commend myself for showing remarkable restraint by not sharing the fate of "Rhapsody in Blue" in real time with the friends with whom I rang in the New Year.  At the very least, I avoided an eye roll or two.) 

The Center for the Study of the Public Domain at Duke Law School has posted a list of some of the now public domain works from 1924 - the year in which Calvin Coolidge was president,  J. Edgar Hoover became head of the FBI, and Truman Capote was born. (Caveat:  I haven't myself verified this list.)   The list includes:

Books:

• Thomas Mann, The Magic Mountain
• E.M. Forster, A Passage to India
• Edith Wharton, Old New York (four novellas)
• Agatha Christie, The Man in the Brown Suit

Films:

• Buster Keaton’s Sherlock, Jr. and The Navigator
• Harold Lloyd’s Girl Shy and Hot Water
• The first film adaptation of Peter Pan

Music:

• "Fascinating Rhythm" and "Oh, Lady Be Good," music George Gershwin, lyrics Ira Gershwin
• "Lazy" by Irving Berlin
• "Santa Claus Blues" by Charley Straight and Gus Kahn

For a different type of list, check out Slate's list of the worst books and films from 1924  (according to critics writing in 1924).  

However, before you go crazy ripping and mixing songs, books, art and films from 1924, you should keep in mind the following.   

1.  The Law is Different Outside the U.S.:  

While works published in 1924 may be in the public domain in the United States, the same works may be subject to copyright protection in other countries. The term for protection for older works in many other countries is the life of the author plus 50 years (e.g., Canada) or 70 years (e.g., many countries in Europe).  (In the U.S., we didn't adopt a "life plus" term of copyright protection until the 1976 Copyright Act.) Accordingly, a work originally published in the U.S. in 1924 by an Italian author who died in 1970 likely remains protected by copyright law in Italy and other countries that use a life plus 70 term of protection. 

So, if you are using a particular work worldwide, you should do more research to determine whether you still need a license.  Here is a list (which I have not verified) of works that may be entering the public domain in 2020 outside the United States based on the year of the authors' deaths.

2.  Derivative Works May Still Enjoy Copyright Protection:  

Only the version of the work, as originally published in 1924, is in the public domain in the U.S. Subsequent adaptations, editions and arrangements by later authors may include original content that is independently protected under copyright law. 

For example, American composer Walter Murphy - the guy behind the disco arrangement of Beethoven's "Fifth Symphony" for the movie Saturday Night Fever - produced a disco-infused recording of "Rhapsody in Blue" in 1977.  The track (available here) is genius and recently was put to good use in an episode of HBO's Watchmen. Murphy's track includes new content that undoubtedly would qualify for copyright protection.  

3.  Watch Out for Sound Recordings:  

Even if a composition (like "Rhapsody in Blue") is in the public domain, it is likely that most preexisting sound recordings of that composition - even 1924 sound recordings! - remain protected under copyright law. The scope and duration of protection for sound recordings is (more than) a little complicated.  But, in a nutshell:

Post-1972 Sound Recordings:  Almost all sound recordings published after February 15, 1972 remain protected under federal copyright law.  (Caveat: a sound recording published in the U.S. without proper notice between February 15, 1972 and March 1, 1989 would be in the public domain, subject to limited exceptions.)

Pre-1972 Sound Recordings:  Until the passage (in 2018) of the The Classics Protection and Access Act (the "CPA Act") (enacted as Title II of the Music Modernization Act), pre-1972 recordings were subject to protection under state ("common law") copyright, not federal copyright law. The scope of that protection was extremely murky (to say the least). The CPA Act, in the words of the Copyright Office, "brings pre-1972 sound recordings partially into the federal copyright system" by providing a federal remedy for certain unauthorized use of pre-1972 sound recordings.  However, the period during which an owner of a pre-1972 sound recording can seek a remedy under the CPA Act for unauthorized uses (referred to as the "term of prohibition" in the statute) is different from the term of copyright protection for works fully covered by the Copyright Act.  The details, which are spelled out in 17 U.S.C. §1401(a)(2)(B), are summarized in this chart: 

So ... applying the above, the owner of a sound recording of "Rhapsody In Blue" first published in 1924 would still have a remedy, under the CPA Act, for the unauthorized use of that recording until January 1, 2025.  Unlicensed users, beware!

Finally, the CPA Act amended the Copyright Act's preemption provisions by adding a new § 301(c) which provides in part:

Nothing in this subsection may be construed to affirm or negate the preemption of rights and remedies pertaining to any cause of action arising from the nonsubscription broadcast transmission of sound recordings under the common law or statutes of any State for activities that do not qualify as covered activities under chapter 14 undertaken during the ["term of prohibition"].  Any potential preemption of rights and remedies related to such activities undertaken during that period shall apply in all respects as it did the day before the date of enactment of the Classics Protection and Access Act."

"Covered activities" under the CPA Act are "any activity that the copyright owner of a sound recording would have the exclusive right to do or authorize under section 106 or 602, or that would violate section 1201 or 1202, if the sound recording were fixed on or after February 15, 1972."  "Covered activities" do not include public performances of sound recordings by means other than digital audio transmission - e.g., a public performance over a terrestrial radio or tv station.  As a result, if a state like California were to recognize a general public performance right in sound recordings - see Flo & Eddie, Inc. v. Pandora Media, Inc. (9th Cir. Oct. 17, 2019) - then that recognition would not be preempted by the CPA Act.  

An in depth discussion of the CPA Act is (WAY) beyond the scope of this post.  If you are interested in more, I recommend Professor Tyler T. Ochoa's thorough post on the topic.

4.  Some Works from 1924  Already Were in the Public Domain:  

Some works published in 1924 already were in the public domain because the copyright owners did not comply with the formalities that were necessary under prior law.  For example, subject to certain exceptions, a work published in the U.S. prior to March 1, 1989 without a copyright notice would be in the public domain. Also, under the 1909 Act, a work would fall into the public domain if the owner did not renew the copyright after an initial 28-year term of protection; accordingly, any work that was initially published between 1925 and 1963 and not renewed fell into the public domain long ago. 

5.  Other Laws May Provide Some Protection:  

We can anticipate that certain rights holders, in certain instances, may try to use trademark law to prevent (or at least limit) the use of their works even after copyright has expired - at least in cases where they believe that consumer confusion is likely as to whether the rights holder was the source of the work or goods in question.  (Mickey Mouse is protected not only by copyright law, but also by trademark law.)  How successful those efforts will be remains to be seen, especially in light of the Supreme Court’s decision in Dastar Corp. v. Twentieth Century Fox.  See also EMI Catalogue Partnership v. Hill, Holliday, Connors, Cosmopulos Inc.

Figuring out the public domain status of a work can be a little tricky.  This handy chart is a good starting place to begin any inquiry.