In the west of England these rings are called “hogs’ tracks.” In the myths and folklore of Sweden they are said to be enchanted circles made by fairies. The elves perform their midnight _stimm_, or dance, and the grass produced after the dancing is called _ailfexing_. A belief prevails in some parts of this country that any one treading within the magic circles either loses consciousness, or can not retrace his steps. Many absurd theories have been propounded as to the cause of these rings. Aubrey, who wrote the _Natural History of Wiltshire_, in the Seventeenth Century, says that they are generated from the breaking out of a fertile subterraneous vapor, which comes from a kind of conical concave, and endeavors to get out at a narrow passage at the top, which forces it to make another cone, inversely situated to the other, the top of which is the green circle. Another remarkable theory by a writer, quoted in Captain Brown’s notes to White’s _Selborne_, attributes these rings to the droppings of starlings, which when in large flights frequently alight on the ground in circles, and are sometimes known to sit a considerable time in these annular congregations. It was also thought that such circles were caused by the effects of electricity, and for this belief the withered part of the grass within the circles may have given foundation. Priestley was a strong advocate of the electric theory, and was supported by many eminent men of his time. “So from the clouds the playful lightning wings, Rives the firm oak, and prints the fairy rings,”