My quick survey of interesting texts coming out of copyright at the start of 2019, the author having died in 1948. It doesn’t seem to be an especially rich year, in terms of the “big names”.
* Alfred Edward Woodley Mason, author of Fire Over England (a beleaguered Queen Elizabeth I prepares for invasion by the tyrannical Spanish), and The Four Feathers (a filmed war novel). Other historical adventure novels such as The House of the Arrow and The Prisoner in the Opal, plus stories and some non-fiction.
* Montague Summers, a poet who also wrote many non-fiction books on belief in vampires and witches. Also Architecture and the Gothic Novel, and The Gothic Quest: a History of the Gothic Novel.
* Denton Welch, novelist and short story writer who influenced William S. Burroughs.
* W. Paul Cook, friend of H.P. Lovecraft and author of the important memoir In Memoriam: Howard Phillips Lovecraft.
* Samuel Whittell Key, author of a series of stories featuring his ‘occult detective’ character Prof. Arnold Rhymer.
* Guy Ridley, author of the tree-ish fantasy The Word of Teregor (1914).
* Jesse Edward Grinstead, popular writer of a great many Wild West novels.
* Rupert Gould, a cryptozoologist who published popular books such as The Loch Ness Monster and Others, A Book of Marvels, and Oddities: A Book of Unexplained Facts.
* Henry Marten, private tutor of Queen Elizabeth II. His pre-PC The Groundwork of British History (1912) became “one of the most used school textbooks of the first half of the twentieth century”. There was a 1923 edition, possibly simply a reprint. His The New Groundwork Of British History in 1943 updated this standard textbook to 1939 and continued its use in schools into the 1950s. But the 1943 edition was a multi-author work, and thus is presumably not going into the public domain. There was a later reprint in 1964. Various versions including 1943 can be freely found on Archive.org.
* D’arcy Wentworth Thompson, who published an acclaimed translation of Aristotle’s The History of Animals.
* Arthur G. T. Applin. An actor and a ‘name’ in the theatre world, as a writer he seems to have been prolific and with a wide range. An early writer for Mills and Boon, with Chorus Girls (1906) and The Stage Door (1909), but his well-reviewed town novels such as Shop Girls (real-life shop-girls of the 1910s) appears to have upped the tone considerably and somewhat evaded ‘the M&B formula’. Later produced countryside books such as Philandering Angler (memoirs of fishing and philandering), popular mysteries such as Blackthorn Farm, and even The Stories of the Russian Ballet. His later reviews in the 1920s and 30s emphasise his ability churn out swift-paced pulp-ish page-turners, with romantic settings ranging from racecourse to desert.
Also of note is S. J. Simon, a popular British mystery and historical-comedy writer, but only because his novels were written with a fellow writer who didn’t die until 1982. Thus his work is not going into the public domain.