Cavorite is an artificial mineral that possesses anti-gravity properties (also referred to as a "gravity-blocking substance"). It can also shield other materials from its effects. Functionally, Cavorite was designed to shield a craft from Earth's pull, allowing easy flight.
The material was invented in the latter half of the 19th century by Doctor Selwyn Cavor. Naming 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 The Doctor stole Professor Cavor's precious Cavorite with plans of using it in the construction of a series of airships. At the behest of the British Intelligence agency MI5, members of The League broke into The Doctor's secret base in Limehouse and recovered the Cavorite sample. The Doctor'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.
Moriarty used the Cavorite in powering his own airship to threaten Britain and bombing London's East End, destroying what is left of The Doctor's criminal empire. The League boarded Moriarty's airship in which the Cavorite was subsequently lost when Mina Murray released it, and allowing to propel into space along with Moriarty who desperately clung to it from letting it escape from his grasp.
In the 1950s rockets and spaceships didn't used cavorite.