Apergy is a fictitious form of anti-gravitational energy first described by Percy Greg in his 1880 sword and planet novel Across the Zodiac.
It is also used by John Jacob Astor IV in his 1894 science fiction novel, A Journey in Other Worlds.
Apergy can also be found in an 1896 article by Clara Jessup Bloomfield-Moore, called "Some Truths About Keely". In it, apergy is used to describe the latent force John Keely harnessed, by using frequency to release the latent force found within all atomic matter.
In an 1897, ostensibly non-fictitious, article in The San Francisco Call titled "The Secret of Aerial Flight Revealed", science correspondent Frank M. Close, D. Sc., visits an unnamed Hindu man masquerading as a viticulturist somewhere on the Pacific coast who claims to have invented a flying boat that uses an "apergent" -- a rare metal called "radlum" -- to produce controlled apergic force, allowing the vessel to ascend and descend. The inventor describes apergy as "a force obtained by blending positive and negative electricity with ultheic, the third element or state of electric energy" and calls apergy a "second phase of gravity", hinting at a third phase as well.
In S. P. Meek's short story "Cold Light", which appeared in Astounding Stories of Super-Science, March 1930, apergy is mentioned as the opposite force of gravity.
In Chris Roberson's short story "Annus Mirabilis" from the 2006 second volume of Tales of the Shadowmen, Doctor Omega and Albert Einstein investigate apergy. Apergy is also mentioned in the Warren Ellis comic Aetheric Mechanics, as being generated by Cavorite technology from The First Men in the Moon.