Although we have had several freezes, the leaves here are just starting to change. Every year, the leaves start changing colors in the North first, and then the color change spreads South. This is not due to the temperature. What causes it?
OK, a puzzle this time. Imagine that you have two steel bars that look alike. One is a magnet and the other is not. Without using anything else (No paperclips, iron filings, etc.) how would you be able to tell which is the magnet?