THE LAND OF THE CHANGING SUN (1894) – By William N. Harben, a former American literary giant who has since been forgotten.
A pair of balloonists – Johnston, an American, and Thorndyke from England – develop a leak in their hot air balloon while flying over the Arctic region.
Spotting a small island, our heroes land on it and build a fire in the slight hope that the smoke may attract any ships in the area. Instead, they are rescued by a futuristic, part-rubber submarine which surfaces by the Arctic island.
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Rather than being rescued, Johnston and Thorndyke are treated as prisoners and given a chemical drink to make them immune to the bends as the sub dives down to the ocean floor. Eventually the vessel surfaces inside an enormous – as in NATION-sized – cavern.
Our main characters are told that they are in the subterranean kingdom called Alpha. Two hundred years earlier, English explorers discovered an abundance of precious metals there. The pioneers gave the vast cavern its name and decided to keep it a secret from the outside world, recruiting Alpha’s inhabitants from people they considered the best that humanity has to offer. Continue reading
UP IN THE AIR AND DOWN IN THE SEA (1863) – Written by William S Hayward, this story was originally serialized in The Boy’s Journal from February to August of 1863. In 1865 it was published in novel form as The Cloud King. 
Years later, when Volans was a teenager, his parents moved the entire family to California to try to cash in on the Gold Rush. Victor took jobs to earn his own money and returned to his ballooning experiments. 
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