Hi. I was thinking about magnetism, and remembered the classic experiment to show magnets working. Basically, you put a magnet under a piece of paper, and drop iron filings on the paper. The filings all line up along lines that curve between the poles. My question is, what are those lines? The first time I saw this experiment, I expected all the filings to just bunch up where the magnet is, why do they 'choose' those certain positions?