Tanar of Pellucidar

The author’s friend Jason Gridley is experimenting with a new radio frequency he dubs the Gridley Wave, via which he picks up a transmission sent by scientist Abner Perry, from the interior world of Pellucidar at the Earth''s core, a realm discovered by the latter and his friend David Innes many years before. There Innes and Perry have established an Empire of Pellucidar, actually a confederation ...