Presumably the newly discovered manuscript has been authenticated in some way (I have not seen any such authentication), but it’s a little confusing what exactly the text is. The story is a little complicated, so it’s probably best to provide a touch of background. In 1924, Lovecraft ghostwrote “Under the Pyramids” (a.k.a. “Imprisoned with the Pharaohs”) for Harry Houdini, and it was published in Weird Tales under Houdini’s name. The magician was impressed with Lovecraft’s writing (which Lovecraft redid in a flurry of activity over his honeymoon on his hated typewriter because he had lost the original manuscript), and Houdini asked Lovecraft to pay him a visit at his New York address, ostensibly to help the struggling author to find employment. They met on October 14, but nothing came of their meeting until 1926, when Houdini asked Lovecraft to ghostwrite an article on astrology, paying $75 for it. I believe that this article is what the eBay manuscript might well be, and others agree.
Presumably impressed by the draft article, Houdini then asked Lovecraft and C. M. Eddy to turn it into a full-scale book. Up until now, scholars believed that all the remained of this effort was an outline and a few introductory pages amounting to a chapter, as S. T. Joshi described in his various books down to An H. P. Lovecraft Encyclopedia (2001). The outline was Lovecraft’s work, but the actual writing was by Eddy, in Joshi’s opinion. This material was published in 1966 in The Dark Brotherhood (Arkham House) and again in 2005 in Collected Essays: Science (Hippocampus), both unread by me. The project ended when Houdini died on October 31, 1926. The trouble is that while the auction catalog suggests that Lovecraft is the author of the typewritten pages, the text itself is more likely from Eddy’s draft than Lovecraft himself.
From a photograph supplied by Potter & Potter, here are the opening lines of the 31-page manuscript, which do not seem to me to be wholly in the style of Lovecraft:
The influence of superstition is far more powerful and widespread than the majority are willing to believe. Its roots planted before history in the mind of mankind, superstition has become a malignant growth which persists with a tenacity little understood. From before the cradle to beyond the grave; sleeping or waking, in sickness or in health, every phase of human existence has its accompanying set of superstitions. The bed on which we lie, the table at which we sit, the food we eat, the work we do, the games we play, the skies above us and the earth beneath --- nothing is free from its contaminating touch. It seems almost incredible in this age of general intellectual advancement that mankind should still be fettered by such a type of prehistoric ignorance. Yet after a century of unprecedentedly rapid scientific progress and nearly five hundred years of modern civilization the vast majority of us are heathens in the innermost recesses of our hearts, and minds, doggedly maintaining a grim hold on our faith in ghosts, magic numbers, witchcraft, incantations, mews and signs, the validity of which has long since been indisputably refuted.
Still, on second thought, this ability of superstition to survive is not difficult to understand or explain. The human mind has an inborn inclination to credit anything which savors of the weird or legendary. Ancestral inheritance, strengthened by the threefold influences of ancient custom, suggestion, and prejudice, and the effects of unsuitable and deficient environment, have given an appearance of validity and authority to that which is actually valueless. …
Not having read the published versions of Cancer, I’m not sure why the counting changed, or whether something in Eddy’s letters revealed more chapters than have previously been published, but the number agrees well with the text up for sale. Given that, it sounds like the “Lovecraft” manuscript, assuming it is genuine, is actually Eddy’s work.