Maxwell’s equations say that electricity and magnetism can’t just leak away. A spinning region of the electric field creates a magnetic field at right angles to the spin. A spinning region of magnetic field creates an electric field at right angles to the spin but in the opposite direction. It was the first major unification of physical forces, showing that electricity and magnetism are intimately interrelated. Maxwell’s equations led us to predict that electromagnetic waves exist, traveling at the speed of light, so light itself is such a wave. This motivated the invention of the radio, radar, television, wireless connections for computer equipment, and most modern communications.

## The Formula to Get 42 Billion Digits of π

While writing "7 Utterly Well-written Math Books About Pi," I found a very interesting math formula that will give you 42 consecutive digits of π accurately but is still wrong.