XI.

The Field Be with You

Faraday introduced the concept of field, which he defined as a space surrounding an object, such as an electron or magnet, in which other objects are subject to or affected by a force. The most common example of field is a magnet attracting iron nails. Faraday pictured the space around the magnet or coil as being 'strained' because of the magnetic force. The field concept emerged painfully over many years in many writings, and historians enjoy arguing about how and when it all came out. Faraday noted in 1832, 'When a magnet acts upon a distant magnet or piece of iron, the influencing cause … proceeds gradually from magnetic bodies and requires time for its transmission.' Thus the concept is that a 'disturbance'—for example a magnetic field—can travel through space and notify a grain of iron powder not only that it is there but also that it can exert a force.

Magnetic lines of force are revealed in an old experiment students do in school, in which they sprinkle iron powder on a sheet of paper placed over a magnet. The student gives the paper a tap to break the surface friction, and the iron powder clusters in a definite pattern of lines connecting the poles of the magnet. Faraday thought these lines were real manifestations of his field concept, and he provided detailed, if ambiguous, descriptions of this alternative to action-at-a-distance. Action-at-a-distance refers to the ability of one object to affect other objects without actually contacting them, and Faraday introduced the concept of the field as an explanation of how this can occur. The field concept was altered, used, and ultimately perfected by Maxwell.