Now, the idea of a hollow Earth was also advocated in 1692 by the famous astronomer Edmund Halley, the same one who discovered the Halley's Comet. He believed that the Earth consisted of shells about 800 km thick, two concentric outer shells separated by atmospheres and having their own magnetic poles, and a central core with diameters similar to those of Venus, Mars and Mercury. Also, the spheres rotated at different speeds. Halley believed that leakage of the inner atmosphere was the cause of the northern lights.<br /><br />In 1818, the American engineer John Cleaves Symes appealed to the American Congress to finance an expedition to search for a passage into the interior of the Earth. On April 15, 1818, members of Congress, the president of the university, and several great scholars received a message:<br /><br />“I declare the earth is hollow and habitable within; containing a number of solid concentrick spheres, one within the other, and that it is open at the poles 12 or 16 degrees… I ask one hundred brave companions, well equipped, to start from Siberia in the fall season, with Reindeer and slays, on the ice of the frozen sea. I engage we find a warm and and rich land, stocked with thrifty vegetables and animals if not men…I pledge my life in support of this truth, and am ready to explore the hollow, if the world will support and aid me in the undertaking. ” - Cleves Symmes, Late Captain of Infantry.
