Are magnetic lines of force "real" ? You know the standard demonstration showing iron filings line up on a piece of paper over a bar magnet to illustrate the magnetic "lines of force?" I'm curious if the line of iron filings really represent places on that plane that are "special" (more "special" than the empty places between them and the next line), and if so, what's so special about them? Or do they just indicate the general shape and direction of the field. Specifically, I'm curious if that experiement with iron filings was repeated several times (with the paper and magnet in exactly the same places), would the iron filings line up in the same place on the paper every time? Or would they just line up generally in the same shape, curving from one pole to the other -- with a line in one experiement just as likely to lie halfway between the places where two lines had fallen on the previous experiment as it would be to fall on exactly the same curve. Thanks !