Possibly of interest to those looking into the historical context for Lovecraft’s “Nyarlathotep” (1920), a new McFarland book Radio Psychics: Mind Reading and Fortune Telling in American Broadcasting, 1920–1940. Apparently not well written, according to one review. But it seems snappy enough in the Google Books excerpts I can obtain, and looks well researched.

April 1919 was when “the restrictions were lifted” on U.S. commercial radio, and it then seems to have been something of a free-for-all? The book also notes early phonograph records in the hypnosis line…

Fitzgibbons had been the first to think of making a “hypnotic record” one could play on one’s phonograph, in order to induce hypnosis (“‘Hypnotic Record’ Brings Out One’s Latent Genius”, Talking Machine World 15.6 (15th June 1919)