The mystery of this wheel is that it seems to revolve automatically without any visible external power. It is at the same time an amusing trick and an instructive experiment. The apparatus required is very simple and can be made at home.

The Wheel as It is Mounted on a Needle, and Lamp and Box Containing Magnet to Make It Turn

Ill: The Wheel as It is Mounted on a Needle, and Lamp and Box Containing Magnet to Make It Turn

A glass bottle is half filled with sand and water, so that it will stand securely, and a cork placed in the neck. Into this cork a needle should be inserted so that it projects perpendicularly, which is most easily done by heating one end of the needle to a red heat and then pushing it into the cork as deeply as possible. Into a disk of cork of suitable thickness and at four points on its side, at equal distances apart, are inserted four pieces of copper wire of the same length, each bent at the outer end to form a hook - these copper wires thus forming the spokes of the wheel. The rim is made of a small iron wire bent in a circular shape and held in the hooks on the ends of the copper wires. The now completed wheel is balanced on the free point on the needle, so that it can turn easily.

Place an alcohol lamp in such a posi-tion that when it is lighted the tip of the flame will just reach the rim of the wheel. (Any other flame that will not soot the rim may be used.) In the box A, placed with its bottom level with the wheel, put a horseshoe magnet so that the flame is opposite one of its poles. After the lamp has been lighted for a few seconds, the wheel will begin to revolve, seemingly without cause. Why does it do so?

Because the magnet magnetizes or attracts the part of the ring nearest it while cold, but not when it is glowing. Instead, it will attract the cooler part of the ring nearest behind the flame and so on, the wheel thus spinning round, faster in the same proportion as the magnet is stronger and the iron rim smaller.

If this experiment is shown before spectators as a trick, the performer may say to the audience that he alone can make the wheel spin around without touching it. Should some one accept his challenge, he may, in a careless way, move the box containing the magnet away or turn it around so that it will not influence the iron ring and then, of course, the wheel will remain immovable.