Book on White Magic is a book found in the library of DeFoe Manor in 5 Days A Stranger. It is used by Trilby to construct a device for finding the body of Matthew DeFoe, and later for finding the body of John DeFoe.
FINDING A PERSON FROM THEIR POSSESSION
Tie the possession in question to a stick and dip it in salt. Next, wave it over the place where the subject sleeps. When you hold it in front of you, the object should now indicate in which direction the owner lies.