Hollow Earth Theory

A map of the Interior World, from The Goddess of Atvatabar (1892).

Early history

In ancient times, the idea of subterranean realms seemed arguable, and became intertwined with the concept of “places” such as the Greek Hades, the Nordic svartalfheim, the Christian Hell, and the Jewish Sheol (with details describing inner Earth in Kabalistic literature, such as the Zohar and Hesed L’Avraham).
Edmond Halley in 1692 put forth the idea of Earth consisting of a hollow shell about 800 km (500 miles) thick, two inner concentric shells and an innermost core, about the diameters of the planets Venus, Mars, and Mercury. Atmospheres separate these shells, and each shell has its own magnetic poles. The spheres rotate at different speeds. Halley proposed this scheme in order to explain anomalous compass readings. He envisaged the atmosphere inside as luminous (and possibly inhabited) and speculated that escaping gas caused the Aurora Borealis.
De Camp and Ley have claimed (in their Lands Beyond) that Leonhard Euler also proposed a hollow-Earth idea, getting rid of multiple shells and postulating an interior sun 1000 km (600 miles) across to provide light to advanced inner-Earth civilization but they provide no references; indeed, it seems that if Euler did propose a hollow-Earth then it was as a thought experiment.
De Camp and Ley also claim that Sir John Leslie expanded on Euler’s idea, suggesting two central suns named Pluto and Proserpine (this was unrelated to the dwarf planet Pluto, which was discovered and named some time later). Leslie did propose a hollow Earth in his 1829 Elements of Natural Philosophy (pp. 449–453), but does not mention interior suns.

19th century

In 1818, John Cleves Symmes, Jr. suggested that the Earth consisted of a hollow shell about 1300 km (800 miles) thick, with openings about 2300 km (1400 miles) across at both poles with 4 inner shells each open at the poles. Symmes became the most famous of the early Hollow Earth proponents. He proposed making an expedition to the North Pole hole, thanks to efforts of one of his followers, James McBride. United States president John Quincy Adams indicated he would approve of this but he left office before this could occur. The new President of the United States, Andrew Jackson, halted the attempt. It is possible this is the source of the (untrue) legend that Jackson believed in a Flat Earth, and was consequently the only United States president to do so.
Jeremiah Reynolds also delivered lectures on the “Hollow Earth” and argued for an expedition. Reynolds went on an expedition to Antarctica himself but missed joining the Great U.S. Exploring Expedition of 1838–1842, even though that venture was a result of his agitation.
Though Symmes himself never wrote a book about his ideas, several authors published works discussing his ideas. McBride wrote Symmes’ Theory of Concentric Spheres in 1826. It appears that Reynolds has an article that appeared as a separate booklet in 1827: Remarks of Symmes’ Theory Which Appeared in the American Quarterly Review. In 1868, a professor W.F. Lyons published The Hollow Globe which put forth a Symmes-like Hollow Earth hypothesis, but failed to mention Symmes himself. Symmes’s son Americus then published The Symmes’ Theory of Concentric Spheres in 1878 to set the record straight.

20th century
The Nazi era Thule Society reported much about Tibetan myths of openings into the Earth. There is even a theory that Hitler ordered a research journey for such an opening in Antarctica, based on a speech of Admiral Dönitz in front of a German submarine in 1944, when he claimed “The German submarine fleet is proud of having built an invisible fortification for the Führer, anywhere in the world.” During the Nuremberg Trials, Dönitz spoke of “an invisible fortification, in midst of the eternal ice.
An early twentieth-century proponent of hollow Earth, William Reed, wrote Phantom of the Poles in 1906. He supported the idea of a hollow Earth, but without interior shells or inner sun.
Marshall Gardner (distinct from Martin Gardner, mentioned below) wrote A Journey to the Earth’s Interior in 1913 and an expanded edition in 1920. He placed an interior sun in the hollow Earth. He even built a working model of the hollow Earth and patented it (U.S. Patent 1,096,102). Gardner made no mention of Reed, but did take Symmes to task for his ideas. In the same time Vladimir Obruchev wrote a fiction novel Plutonia, where the hollow Earth’s interior possessed one inner (central) sun and was inhabited by prehistoric species. The interior was connected with the surface by a hole in the Arctic.
Other writers have proposed that “ascended masters” of esoteric wisdom inhabit subterranean caverns or a hollow Earth. Antarctica, the North Pole, Tibet, Peru, and Mount Shasta in California, USA, have all had their advocates as the locations of entrances to a subterranean realm referred to as Agartha, with some even advancing the hypothesis that UFOs have their homeland in these places.
A book allegedly by a “Dr. Raymond Bernard” which appeared in 1964, The Hollow Earth, exemplifies this idea. The book rehashes Reed and Gardner’s ideas and ignores Symmes. Bernard also adds his own ideas: the Ring Nebula proves the existence of hollow worlds, as well as speculation on the fate of Atlantis and the origin of flying saucers. “Bernard” argued that the inhabitants of Atlantis took refuge in the Earth’s interior before the city was destroyed in great calamity.It was Atlanteans who piloted the flying machines known in ancient India as vimanas and in the modern world as flying saucers. After the US bombings of Hiroshima and Nagasaki, Bernard claimed, the Atlanteans became concerned that radioactive air might flow into the world’s interior, and so some emerged in their flying saucers in an act of self-defense. An article by Martin Gardner revealed that Dr.Walter Siegmeister used the pseudonym `Bernard’, but not until the publishing of Walter Kafton-Minkel’s Subterranean Worlds: 100,000 years of dragons, dwarves, the dead, lost races & UFOs from inside the Earth, in 1989, did the full story of Bernard/Siegmeister become well known.
The pages of the science fiction pulp magazine Amazing Stories promoted one such idea from 1945 to 1949 as “the Shaver Mystery”. The magazine’s editor, Ray Palmer, ran a series of stories by Richard Sharpe Shaver supposedly claimed as factual, though presented in the context of fiction. Shaver claimed that a superior pre-historic race had built a honeycomb of caves in the Earth, and that their degenerate descendants, known as “Dero”, live there still, using the fantastic machines abandoned by the ancient races to torment those of us living on the surface. As one characteristic of this torment, Shaver described “voices” that purportedly came from no explainable source. Thousands of readers wrote to affirm that they, too, had heard the fiendish voices from inside the Earth.
Fantastic stories (supposedly believed as factual within fringe circles) have also circulated that Adolf Hitler and some of his followers escaped to hollow lands within the Earth after World War II via an entrance in Antarctica. (See also Hitler’s supposed adherence to concave hollow-Earth ideas, below.)
Some writers have proposed building megastructures that have some similarities to a hollow Earth