Magnetic and electric fields exist nearly everywhere, and the following is a brief description of what these fields are, how they are created, and what effects they produce. The concept of an "electric field" arose when electrons were observed to repel other electrons but attract protons. This attraction-repulsion was actually seen before the discovery of electrons or protons; early measurements studied the forces on objects that happened to acquire an excess or deficiency of electrons after being rubbed with cloth or fur. If two electrons are separated by one centimeter, each electron will experience a repulsive force of 2.3 x 10-24 gram-equivalents. Doubling the separation will reduce the force to one quarter. Doubling the number of electrons on one side will double the repulsive force acting on the lone electron on the other side. Most matter is neutral, so it contains an equal number of protons and electrons . However, sometimes electrons are deliberately or accidentally removed from one object, and deposited onto another object. If a proton (or other positive-charged body) is placed near these two charged objects, the proton will be attracted to the negative object, which has excess electrons, and simultaneously repelled from the positive one, which is missing some electrons. The total force acting on the proton is a measure of the electric field that the proton is exposed to. The direction of the force that acts on the proton is the same as the direction of the electric field and the strength of the force is proportional to the strength of the electric field. (The force that acts on the proton, in gram-equivalents, multiplied by 6 x 1016, gives the electric field in units of volts per meter or V/m.) If an electron were substituted for the proton, the force would be of the same strength but in the opposite direction of the electric field. If two protons "tied" together were substituted for the single proton, they would experience twice as much total force.