John Napier used his Black Rooster to find out the servants stealing from his home

John Napier of Merchistoun (1550 – 4 April 1617) was a Scottish mathematician, physicist, astronomer/astrologer. He is most remembered as the inventor of logarithms and Napier's bones, and for popularizing the use of the decimal point.

In addition to his mathematical and religious interests, Napier was commonly believed to be a magician, and is thought to have dabbled in alchemy and necromancy. Necromancy is a form of divination in which the practitioner seeks to summon "operative spirits" or "spirits of divination", for multiple reasons, from spiritual protection to wisdom. However, since the Renaissance, necromancy has come to be associated more broadly with black magic and demon-summoning in general, sometimes losing its earlier, more specialized meaning. It was said that he would travel about with a black spider in a small box, and that his black rooster was his familiar spirit. In early modern English superstition, a familiar spirit is an animal-shaped spirit who serves for witchery, a demon, or other magician-related subjects.

Napier used this rooster to find out which of his servants had been stealing from his home. He would shut the suspects one at a time in a room with the bird, telling them to stroke it. The rooster would then tell Napier which of them was guilty. Actually, what would happen is that he would secretly coat the rooster with soot. Servants who were innocent would have no qualms about stroking it but the guilty one would only pretend he had, and when Napier examined their hands, the one with the clean hands was guilty.

Another occasion which may have contributed to his reputation as a sorcerer involved a neighbour whose pigeons were found to be eating Napier's grain. Napier warned him that from now on he intended to keep any pigeons found on his property. The next day, it is said, Napier was witnessed surrounded by unusually passive pigeons which he was scooping up and putting in a sack. The previous night he had soaked some peas in brandy, and then sown them. Come morning, the pigeons had gobbled them up, rendering themselves incapable of flight.

Also of note is that a contract still exists between John Napier and one Robert Logan of Restalrig to search Fast Castle (by means of magic) for treasure allegedly hidden there, and wherein it is stated that Napier should "...do his utmost diligence to search and seek out, and by all craft and ingine to find out the same, or make it sure that no such thing has been there."

"The Love Potion" by Evelyn de Morgan: a witch with a black cat familiar at her feet