In 1566 Paracelsus, a German physician, alchemist and philosopher published a tract On Nymphs, Sylphs, Pygmies, and Salamanders. He categorized the denizens of Faerie, known by many different names in folklore, as different types of elemental beings.

The name of the water people [nymphs] is also undina, and of the air people [sylphs] sylvestries, and of the mountain people [pygmies] gnomi, and of the fire people vulcani rather than salamandri.

On Nymphs, Sylphs, Pygmies, and Salamanders

You know that there are four elements, air, water, earth and fire; and you also know that we, men from Adam, stand and walk in air and are surrounded by it as a fish by water, and can just as little be without it as a fish without water. As the fish has it’s abode in water, where water takes for it the place of the air in which it lives, so air takes for man the place of water,in relation to the fish.

Thus everything has been created in its element, to walk therein. From this example you understand that the undinae have their abode in water, and the water is given to them as to us the air, and just as we are astonished that they should live in water, they are astonished about our being in the air.

The same applies to the gnomi in the mountains: the earth is their air and is their chaos. For everything lives in chaos. That is: everything has its abode in chaos, walks and stands therein. Now the earth is not more than mere chaos to the mountain manikins, for they walk through solid walls, through rocks and stones, like a spirit; this is why these things are all mere chaos to them, that is, nothing…

That amounts to: as little as we are hampered by the air, as little as they are hampered by the mountain, by earth and rocks. And as it is easy for us to walk through air and air cannot stop us, so rocks and cliffs are easy to them. And so, things are all chaos to them which are not chaos to us, for a wall, a partition, stops us so that we cannot go through, but to them it is a chaos. That is why they walk through it; to them it is their air in which they live and walk, as man does in the air that is between heaven and earth. And the coarser the chaos, the more subtle is the creature; and the more subtle the chaos the coarser the creature. The mountain people have a coarse chaos; therefore they must be more subtle; and man has a subtle chaos; therefore, he is all the coarser…

…Know also that two of them, namely the earth manikins and vulcans, are considered spirits and not creatures, being looked on as a mirage only, or as ghosts, You must know, however, that just as they appear, thus they are, flesh and blood like another man, and with that, quick and fast like a spirit, as was told in the beginning.

On Nymphs, Sylphs, Pygmies, and Salamanders

This was and interesting book to read, as the existence of these types of creatures was not in question, just something to be studied. The only existential question seemed to be whether nymphs, sylphs, gnomes,etc. had a soul, like man (He did not think so).

He was writing centuries before the discovery of the electromagnetic spectrum, frequencies or even ideas of different dimensions and vibrations, but had an insightful way of it relating to the properties of the four elements.