Like some other books of his later years, in this novel Verne tempers his love of science and engineering with a good dose of irony about their potential for harmful abuse and the fallibility of human endeavors.

In the year of 1890, an international auction is organized to define the sovereign rights to the part of the Arctic extending from the 84th parallel, the highest yet reached by man, to the North Pole.

Maston and Captain Nicholl — the same members of the Baltimore Gun Club who, twenty years earlier, had traveled around the Moon inside a large cannon shell.

The brave gunmen-astronauts had come out of their retirement with an even more ambitious engineering project: using the recoil of a huge cannon to remove the tilt of the Earth's axis — so that it would become perpendicular to the planet's orbit, like Jupiter's.

The cannon in fact had been dug deep into the flanks of Mount Kilimanjaro, by a small army of workers provided by a local sultan who was an enthusiastic fan of the former Moon explorers.

The projectile, a steel-braced chunk of rock weighing 180,000 tons, would exit the barrel at the fantastic speed of 2,800 kilometres per second — thanks to a new powerful explosive invented by Nicholl, which he had called "melimelonite".