People with robotic wings, people that can learn the language of a person while he/she sleeps? Birds trained to sing in duets and trios like no others in the Earth? All this happening deep inside a huge cave, humans not aware of?
Yes; in Edward Bulwer-Lytton' novel The Coming Race, there is an underground civilization that can control their climate, that can influence other people's mind, and their environment, their vegetation and their animals. They have the power of the Vril.
Bulwer-Lytton expresses a thought that can lead to powerful mind-controlling experiences like mesmerism, telepathy, and clairvoyance:
Zee asked me if, in my world, it was not known that all the faculties of the mind could be quickened to a degree unknown in the waking state, by trance or vision, in which the thoughts of one brain could be transmitted to another, and knowledge be thus rapidly interchanged.
According to their tradition, they are the descendants of tribes the sought refuge under caverns when some kind of Deluge --a big Flood-- that changed the face of the Earth. "Wandering through these hollows, they lost sight of the upper world forever." Their place is not a mere huge cave, we should think of it as the size of a modern big city like New York, or Paris, or Berlin.
The Vril is a form of energy that was slowly discovered the inhabitants of that underground city.
It can destroy like the flash of lightning; yet, differently applied, it can replenish or invigorate life, heal, and preserve, and on it they chiefly rely for the cure of disease, or rather for enabling the physical organisation to re-establish the due equilibrium of its natural powers, and thereby to cure" itself.
These people call themselves the Vril-ya, a term that stands for: "The Civilised Nations". For this reason all theological speculations is eluded.
Vril was also used for some kind of health-bath like those we see with thermal baths. The Vril is an all-encompassing substance that penetrates every aspect of their life, even their religion:
This people have a religion, and, whatever may be said against it, at least it has these strange peculiarities: firstly, that all believe in the creed they profess; secondly, that they all practice the precepts which the creed inculcates. They unite in the worship of one divine Creator and Sustainer of the universe. They believe that it is one of the properties of the all-permeating agency of vril, to transmit to the well-spring of life and intelligence every thought that a living creature can conceive
However, even when they had some form of Bible-like ancient manuscripts "these were found to lead to such heated and angry disputations as not only to shake the peace of the community and divide families before the most united, but in the course of discussing the attributes of the Diety, the existence of the Diety Himself became argued away, or, what was worse, became invested with the passions and infirmities of the human disputants". With these words, the author criticizes the multitude of Biblical interpretations that fuel angry disputes and never-ending wars among ourselves. Same goes for other sacred texts of the many religions humans have invented.
In chapter XVI, Bulwer-Lytton describes a kind of walking staff the Vril-ya use for multiple activities from destroying to healing. "It is usually carried in the convenient size of a walking-staff, but it has slides by which it can be lengthened or shortened at will."
The Vril fluid was so potent that it was capable to "... reduce to ashes within a space of time too short for me to venture to specify it, a capital twice as vast as London." No wonder some people attribute to the Hitler's army an intense search for such a weapon. Keep in mind that the World War took effect by decade of the 1940's, and that Bulwer-Lytton wrote his novel The Coming Race long after that, by the year 1871; so the Vril-power was very well-known by the general public and by Hitler's generals as well.
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