Great IdeasNature and science
Electricity and magnetism
Lodestones, sparks and the forces that run motors.
The question
What are magnetism and electricity, and how did people find out they are connected?
How the books answer
Oldest first. Each stop is our own short summary of what the author argued; follow the link to the rung for the whole lesson.
c. 55 BC
Lucretius, On the Nature of Things (in the set: The Way Things Are)
Lucretius tries to explain the magnet, a stone that pulls iron, using atoms. He suggests that streams of atoms flowing from the stone clear a space, and iron atoms rush in. The explanation was wrong, but it treated magnetism as natural, not magic.
late 2nd century AD
Galen, On the Natural Faculties
Galen uses the lodestone as a comparison. Just as the stone draws iron, he argues, the organs of the body draw to themselves what they need. He believed living bodies have attractive powers like the magnet's.
“It has to do with the famous and far-renowned stone which draws iron [the lodestone].”
1600
William Gilbert, On the Loadstone and Magnetic Bodies
Gilbert tested old claims with experiments, and threw out myths such as that garlic stops a magnet. Using a small round magnet as a model, he showed the earth itself is a great magnet, which is why compasses point north. He also studied how rubbed amber attracts things, and his Latin word electricus gave English the word electric.
“Hence some suspect that garlick is of avail against any deleterious power of the magnet: thus in philosophy many false and idle conjectures arise from fables and falsehoods.”
1832–1855
Michael Faraday, Experimental Researches in Electricity
Faraday discovers that a changing magnetic field makes electric current flow in a wire. He pictures lines of force filling the space around magnets and currents. His discoveries are the basis of the electric generator and transformer.
“When the contact was made, there was a sudden and very slight effect at the galvanometer, and there was also a similar slight effect when the contact with the battery was broken.”
Go to the rung: Faraday: Experimental Researches in Electricity
1916 (English 1920)
Albert Einstein, Relativity: The Special and the General Theory
Einstein's relativity grew partly from a puzzle in electricity and magnetism. Moving a magnet near a wire or a wire near a magnet gives the same current, yet the old theory described the two cases differently. Relativity shows that electricity and magnetism are two sides of one thing.
For young readers
Magnets pull on iron and stick to the fridge. A compass needle is a little magnet that points north, because the whole earth is a giant magnet! William Gilbert figured that out over 400 years ago.
Electricity is what lights your lamps. Michael Faraday found that moving a magnet near a coil of wire makes electricity. That's how power stations make electricity today: spinning magnets and wires.
Talk about it
- Rub a balloon on your hair. What happens when you hold it near small bits of paper?
- Gilbert tested whether garlic stops a magnet. Why was it important to test old claims?
- How does a compass work?
- What things in your home use electricity? What would life be like without it?
Where else on the site
- Magnets and Magnetic Fields
- Magnetic Fields and Their Sources
- Attraction and Repulsion
- Generators and Induction
- Faraday's Law
- Using a Compass
Every rung tagged with this idea:
These pages are our own short synthesis, written for families. They were inspired by Mortimer J. Adler's Syntopicon, the index of great ideas in volumes 1 and 2 of Great Books of the Western World, but the questions, summaries and groupings are ours, not the Syntopicon's. Short excerpts come from public-domain translations, credited where they appear.