Cavorite was a material created across several different universes that negated or reversed the pull of gravity, and extended that power to whatever craft it was housed in.
League of Extraordinary Gentlemen: Doctor Selwyn Cavor
Cavorite was an artificial mineral that possessed anti-gravity properties (also referred to as a "gravity-blocking substance"). It could also shield other materials from its effects. Functionally, Cavorite was designed to shield a craft from Earth's pull, which allowed easy flight. The material was invented in the latter half of the 19th century by Doctor Selwyn Cavor, who named it after himself. Cavor offered the use of Cavorite to the British Empire for a planned lunar expedition scheduled to take place at the turn of the century.
In July of 1898 however, Chinese criminal mastermind Fu Manchu stole Professor Cavor's precious Cavorite with plans of using it in the construction of a series of flying ships. At the behest of the British Intelligence agency MI5, members of the League of Extraordinary Gentlemen broke into Fu Manchu's secret base in Limehouse and recovered the Cavorite sample. Fu Manchu's men burst into the chamber to stop them, but the group linked hands, and unlocked the mineral's containment device. The Cavorite propelled them through the top of the tunnel into the Thames River. The League brought the Cavorite back to their employers at British Intelligence, not realizing at the time, that they were actually delivering it into the hands of the "Napoleon of Crime", Professor James Moriarty.
Earth-One: Ferdinand Alt
The Atom was conscripted by the Central Intelligence Agency to retrieve a model of a craft that was powered by actual Cavorite; hidden in a toy store in Austria. After several suspicious near-fatal experiences, the Atom retrieved the miniature craft but concluded that the Cavorite was actually a trap set by America's "cold war enemies".
The Cavorite was developed by Ferdinand Alt, who described it as a metallic element that needed to be charged up with electrons in order to effectively produce anti-gravity. As the electrical charge continued to build, the Cavorite would become radioactive and ultimately achieve a critical mass in an explosion that would destroy the continental U.S.
The Atom saw through the plot by the double-agent Alt, and ultimately had the government put Alt's Cavorite in cold storage, where it presumably stayed.
- As the double agent Ferdinand Alt notes, Cavorite's namesake Doctor Cavor was a fictional scientist created by novelist H. G. Wells and first appeared in the 1901 novel The First Men in the Moon.
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