KINGDOMS OF ELFIN by SYLVIA TOWNSEND WARNER 222 pages. Viking. $8.95.
AN ENCYCLOPEDIA OF FAIRIES
by KATHARINE BRIGGS 481 pages. Pantheon. $12.95.
If man had not invented them, fairies would have to exist. How else could mortals account for lost objects and the malfunctions of the material world? It was no accident that a new strain of elvesgremlinsmagically appeared at about the time of World War II, when things began going wrong with airplanes. For centuries the presence of fairies helped temper parental rage at the misbehavior of children; the ethereal little devils were responsible....