It contains abundant speculation about technological invention, including descriptions of a worldwide telephone network, solar power, air travel, space travel to the planets Saturn and Jupiter, and terraforming engineering projects — damming the Arctic Ocean, and an adjustment of the axial tilt of the Earth (Terra) by the Terrestrial Axis Straightening Company.

European nations have been taken over by socialist governments, which have sold most of their African colonies to the U.S., while Canada, Mexico, and the countries of South America have requested annexation.

Jupiter proves to be a jungle world, with flesh-eating plants, vampire bats, giant snakes and mastodons, and flying lizards.

The Americans discover a wealth of exploitable resources: iron, silver, gold, lead, copper, coal, and oil.

One of the spirits, a deceased bishop, tells the voyagers about the icy world Cassandra, which orbits the Sun beyond Neptune and is home to the souls of unworthy Earthlings.