There are two hollow earth theories. According to the first one we live on the crust, but there is another world on the inside where lies - some say - the realm of Agartha, the home of the King of the World (see, for example, the fantasies of French philosopher RenÃÂ™uÃµsn). The second theory has it that while we think we live on the outer crust, we actually live in the interior (on a convex surface instead of a concave one).One of the first hollow earth theories was proposed in 1692 by the English astronomer Edmund Halley (discoverer of the now-famous comet), who suggested that the Earth was composed of four spheres, each embedded in the others like so many matryoshka dolls, illuminated by a luminous atmosphere and perhaps inhabitable. The theory was reproposed in the early 19th century by J Cleves Symmes of Ohio, who wrote to various scientific societies: "To all the world: I declare that the Earth is hollow and habitable within; containing a number of solid concentric spheres, one inside the other, and that it is open at the poles 12 or 16 degrees." Symmes believed that at the north and south poles there were two apertures that led to the interior of the globe. He attempted to raise funds for an exploration of the polar regions to locate these entrances. The Philadelphia Academy of Natural Sciences still has a wooden model he used to explain his theories. The idea was later championed by Jeremiah Reynolds, a newspaper editor, who took it upon himself to promote the expedition at the expense of the American government (a request ultimately denied). The journey was unsuccessful, since he and his party were thwarted by Antarctic ice. At the end of the century the theory was revisited by cult leader Cyrus Reed Teed, who said that what we believe is the sky is a gaseous mass that fills the interior of the globe with areas of bright light (sun, moon and stars would not be heavenly bodies but visual effects). It is widely rumoured on the internet that the hollow earth theory was taken seriously by top-ranking Nazis who believed in the occult sciences.
In some circles of the German navy it was purportedly believed that the hollow earth theory would make it easier to pinpoint the exact position of British ships because, if infrared rays were used, the curvature of the Earth would not have obscured observation. Hitler allegedly sent an expedition to the Baltic island of R?here a Dr Heinz Fischer trained a telescopic camera toward the sky in order to spot the British fleet sailing on the interior of the convex surface of the hollow earth. It is even said that some V1 missiles went astray because their trajectory was calculated on the basis of a hypothetical concave surface instead of a convex one.