CHANGELINGS.  
Sometimes the fairies fancy mortals, and carry them away into their own country, leaving instead some sickly fairy child, or a log of wood so bewitched that it seems to be a mortal pining away, and dying, and being buried. Most commonly they steal children. If you "over look a child," that is look on it with envy, the fairies have it in their power. Many things can be done to find out in a child a changeling, but there is one infallible thing—lay it on the fire with this formula, "Burn, burn, burn—if of the devil, burn; but if of God and the saints, be safe from harm" (given by Lady Wilde). Then if it be a changeling it will rush up the chimney with a cry, for, according to Giraldus Cambrensis, "fire is the greatest of enemies to every sort of phantom, in so much that those who have seen apparitions fall into a swoon as soon as they are sensible of the brightness ............