One simple experiment students often conduct is to place two magnets on a table with opposite poles facing each other but not touching.
A piece of paper is placed on top of the magnets and iron filings are dropped on top of the paper above the magnets.
Friction keeps the iron filings from moving much, but if the paper is tapped lightly, the filings twist their way toward the magnets in lines.
The lines directly between the magnets are straight, and the lines farther outside the magnets are curved.
Scientists had noticed this phenomenon for centuries, but Faraday saw tremendous meaning in it. He called the lines “magnetic lines of force” and said they moved outward great distances from the poles.
He said this is why a compass would work such a great distance from Earth’s polar regions.
Faraday measured the strengths of these magnetic fields and observed the different directions of the lines. He did not have the mathematical training to study them further, however.
Faraday thought other forces, like gravity, electricity, and even light, all acted with these lines of force, or fields.
He took the theory one step further and said that matter itself extended beyond its visible edges and filled all space. We know there are gravitational and electrical fields but Faraday’s theory was so advanced that some of it is still being tested today.
The twentieth-century physicist Albert Einstein used field theory in much of his work and another field has now been discovered.
The forces around the nucleus of the atom are known as nuclear fields.