The concept of magnetic lines of force was invented by Michael Faraday and is useful in understanding magnetic and electrostatic phenomena. It is defined in the following way: on a sphere with a radius of one centimeter surrounding a unit pole, each square centimeter will contain a single line of force. The surface of a sphere is 4πr2, thus the total number of lines of force due to a unit pole is 4π. Again, it should be understood that these magnetic lines are purely imaginary. But the concept is a useful study tool, and many technicians are in the habit of referring to magnetic lines as if they actually exist in the space around every magnet.