Lovecraft’s famous survey of supernatural literature was published in The Recluse in August 1927. Later in the same year Eino Railo published the history of the literary gothic in The Haunted Castle: A Study of the Elements of English Romanticism. A December 1927 review in the New York Evening Post suggests Railo’s book was published in time for the Christmas market and the January book-token crowd, and thus it appeared several months after Lovecraft’s circle had finished digesting his Supernatural Literature. Lovecraft refers to The Haunted Castle, a translation from the Finnish, in admiring terms in a later letter to Barlow and terms it a study of “the weird”.

Rather surprisingly Wikipedia has no page in English for Eino Railo, an important literary historian of the early 20th century. But using Google Translate on his Finnish page shows the book was originally his thesis in Finnish, Haamulinna (1925). Thus, even though there was at least one young Finn on the fringes of Lovecraft’s circle, it initially seems highly unlikely that Lovecraft would have read the book before writing Supernatural Literature. However, consider that the Finnish thesis must have taken a while to translate to English. This was done for Routledge, for an English edition to be published in both London and New York. As such it’s not impossible that news of the translation was circulating in New York weird and publishing circles, and circulating while Lovecraft was living and socialising in New York. Certainly the Routledge office in New York must have been aware, by the late summer, of what they had set for publication shortly before Christmas 1927.

Joshi says of the book, in his Icons Of Horror And Supernatural…

In 1927 Eino Railo published the definitive and entertaining The Haunted Castle: A Study of the Elements of English Romanticism, providing a virtual Baedeker to the castle — forerunner of the haunted house — and other elements of gothic literature.

Given this praise and the date of publication, it must form an important touchstone for “what Lovecraft knew of” in the older non-pulp weird, by circa early 1928, and also what his circle was aware of in terms of their literary forebears.

While not yet online in full, the book does have a 4,000 word contents-list, which can be found online if you seek hard enough.