Magnets were well known the Greeks in antiquity[1], likely because of the Magnesia region in Greece where natural magnets are commonly found[2]. Words like "magnet" and "magnetite" are named after that region.

In 1584, the magnetic compass would have been well known and understood, but the connection between electricity and magnetism was a long way off. Gilbert's De Magnete[4], which explained that compasses worked because the earth itself had a magnetic field, was published in 1600, not long after this book on "Magick."

[1]: https://en.wikipedia.org/wiki/Magnes_the_shepherd

[2]: https://en.wikipedia.org/wiki/Magnesia_Prefecture

[3]: https://en.wikipedia.org/wiki/Magnetite

[4]: https://en.wikipedia.org/wiki/De_Magnete