There was a time, many decades ago, when cute and nubile female undergraduates used to come into my office and perch pertly on my desk, giving me a fine view of various features, while discussing trivia but really angling for a higher grade. It never worked and the cute female students are long gone, but for the past several weeks there's been something very cute indeed perched on one side of my desk. It is small, and you really need a desk magnifying glass to get a good look. It consists of four tiny, metallic cubical magnets assembled into a platform. Hanging mysteriously in mid-air above the magnets is what looks like and is a tiny, thin square of graphite. This is a demonstration of “diamagnetic levitation,” and the idea is very simple indeed. Atoms and molecules are not rigid objects. If you place any material in a strong magnetic field, the molecules are distorted in such a way that each of them develops its own magnetic field. If you ever had a college course in electricity and magnetism, you will remember that such “induced” fields always oppose the external field that induced them. Therefore, with the right geometry, you might think you can levitate any material above a strong enough magnet, achieving a magnetic repulsion that just balances gravity. Well, in practice, the only material that develops a significantly strong induced magnetic field is a type of graphite, and even so, the effect is very, very weak. But with strong magnets and a small and thin sheet of graphite, the effect is quite impressive, as the photos indicate.

The easiest way to play with the phenomenon is to purchase a “diamagnetic levitation kit” from some mail-order company that supplies science-related items to teachers and the educated minority. I got mine from American Science and Surplus for about ten dollars; avoid companies that charge more, because what you will get is indeed worth about $10. You get the four cubical magnets and two pieces of graphite and that's all you need. You may be disappointed in the degree of levitation you get at first. The kit instructions will give hints as to how to improve it; the most difficult of them is splitting your sheet of graphite in two, to halve its mass while maintaining the same area. Want to learn more? Check this reference.  Some kits include a tiny metal-coated plastic disk (shown in two of the  three photos) which has nothing to do with the effect, but serves to make the four magnets easy to carry around in a pocket for display.