The Perfect World / A romance of strange people and strange places

This is another rare fantasy novel of: Origin of the People; The Light; The End of the World; In Space; Adrift in the Solar Regions; Jupiter and the Jovians; Death in Jupiter; Alan The Knight Errant; The Cave of Whispering Madness; The Hall of Sorrows; The Perfect World, etc. Stunted descendants of the lost tribes found in an interior world. This is of interest to those researching the hollow earth. 

It's almost two stories. First, Allen and Desmond are in a small mining town from which a mysterious (light?) causes people to disappear. When it snatches Allen and Desmond, they find themselves deep underground where God had cast those who rebelled against Moses. Most of the snatched people are sacrificed to a fire which must be kept fed lest the Earth die. As the fire declines, Allen and Desmond escape to Earth's surface. Fortunately, for them, their uncle has build a great airship in the meantime and they ride this as the Earth erupts and dies.

Part 2 has the airship making its way to Jupiter. There a basically sinless (although stratified) society exists with benevolent monarchy / theocracy. Allen develops an infatuation with a princess who is expected to choose a husband from several local princes. When one prince learns of Allen's feelings towards the princess, the prince gets a sinful obsession with her. Eventually, the prince abducts the princess in hopes of making her accept him. Of course, Allen goes to great lengths to save the princess, who falls in love with him.