This is an entertaining history of the idea of a hollow Earth, from what at the time was serious scientific speculation (concentric Earths supposedly explaining why the magnetic poles don’t line up with the geographical ones) to crank theorizing to 19th– and 20th-century science fiction. Standish is not completely consistent in what he counts as “hollow Earth,” however. He makes a point of omitting works that hypothesize large systems of caverns, but then he includes Verne’s Journey to the Center of the Earth, which in which the Earth isn’t hollow but merely has a large interconnected system of caves under parts of the North Atlantic and Western Europe.
But overlooking that inconsistency and a few errors and omissions, I enjoyed this reasonably well-written and voluminously researched book. A few of the 19th-century SF adventures he describes sounds like they might be worth reading as well. As in Edgar Rice Burroughs’s At the Earth’s Core, most of them envisioned a hollow Earth with an inhabited inner surface (though unfortunately gravity doesn’t work that way) reachable through holes in the polar regions. That idea was originally proposed, quite seriously, by an eccentric former American Army officer named John Cleves Symmes, Jr. in 1818, and he lectured on it extensively until his death in 1829. A Hollow Earth monument erected by his son Americus now stands above his grave in Symmes Park in Hamilton, Ohio.
Of the other hollow-Earth notions mentioned in this book, the oddest may be the hypothesis that the universe is solid rock and we ourselves live on the underside of a spherical bubble. Some think Hitler believed this and ordered German scientists to investigate the military possibilities.
Hollow Earth is quite readable if rambling, full of wild ideas and odd characters.