The friendly daemon, or The generous apparition

being a true narrative of a miraculous cure, newly perform'd upon that famous deaf and dumb gentleman, Dr. Duncan Campbel, by a familiar spirit that appear'd to him in a white surplice, like a cathedral singing boy.

de Daniel Defoe

Consists of two letters, supposedly by Campbell, the first dealing with his illness and cure; the second with genii or familiar spirits and a "sympathetic powder" brought from the East. Cf. Dict. nat. biog.