Just as visible Nature is populated by an infinite number of living creatures, so, according to Paracelsus, the invisible, spiritual counterpart of visible Nature (composed of the tenuous principles of the visible elements) is inhabited by a host of peculiar beings, to whom he has given the name elementals, and which have later been termed the Nature spirits. Paracelsus divided these people of the elements into four distinct groups, which he called gnomes, undines, sylphs, and salamanders. He taught that they were really living entities, many resembling human beings in shape, and inhabiting worlds of their own, unknown to man because his undeveloped senses were incapable of functioning beyond the limitations of the grosser elements.The civilizations of Greece, Rome, Egypt, China, and India believed implicitly in satyrs, sprites, and goblins. They peopled the sea with mermaids, the rivers and fountains with nymphs, the air with fairies, the fire with Lares and Penates, and the earth with fauns, dryads, and hamadryads. These Nature spirits were held in the highest esteem, and propitiatory offerings were made to them.Occasionally, as the result of atmospheric conditions or the peculiar sensitiveness of the devotee, they became visible. Many authors wrote concerning them in terms which signify that they had actually beheld these inhabitants of Nature’s finer realms. A number of authorities are of the opinion that many of the Gods worshiped by the pagans were elementals, for some of these invisibles were believed to be of commanding stature and magnificent deportment.The Greeks gave the name dæmon to some of these elementals, especially those of the higher orders, and worshiped them. Probably the most famous of these dæmons is the mysterious spirit which instructed Socrates, and of whom that great philosopher spoke in the highest terms. Those who have devoted much study to the invisible constitution of man realize that it is quite probable the dæmon of Socrates and the angel of Jakob Böhme were in reality not elementals, but the overshadowing divine natures of these philosophers themselves.