Girolamo Cardano was a doctor, astrologer, mathematician, and natural philosopher who helped create modern algebra and invented the universal joint.  He was encouraged to study the classics, mathematics, and astronomy by his father, a friend of Leonardo da Vinci.   He completed his university studies in Padua in 1526 with a degree in Medicine.  He became very successful and well known throughout Europe.  He published many works including this one, which covers a broad range of topics including cosmology, construction of machines, the usefulness of the natural sciences, the influence of demons, the laws of mechanics, and cryptology¹¹. Also included is a summary of the differences between the amber effect (electricity) and lodestone (magnetic) phenomena, including¹⁴:

1) amber draws many kinds of bodies, the lodestone only iron
2) the attraction between lodestone and iron is mutual, the amber effect is not
3) the lodestone, unlike amber, acts across interposed objects
4) the magnet pulls only toward its poles, amber everywhere
5) amber's force is improved by gentle heat and friction, which do not affect the magnet's

It was these qualities that influenced William Gilbert's De Magnete (see following page.) Gilbert accepted Cardano's observations but soundly criticized his conclusions.