books.google.com - Beliefs in mysterious underworlds are as old as humanity. But the idea that the earth has a hollow interior was first proposed as a scientific theory in 1691 by Sir Edmond Halley (of comet fame), who also suggested that there might be life down there as well. Hollow Earth traces the many surprising,...http://books.google.com/books/about/Hollow_Earth.html?id=J1BC7eFLBFcC&utm_source=gb-gplus-shareHollow Earth
