Does the strength of a magnetic field become weaker at a constant rate the further you get away from it? I ask this question for two reasons. 1 - When iron filings are placed on a piece of paper and and a magnet is placed under it, there are definite lines of magnetic force visible that become less obvious the further they are away from the magnet. 2 - When I was into electronics, I built a crystal radio and attached a single transistor amplifier to it. I then removed the tuning coil and replaced it with a single piece of wire and replaced the tuning capacitor with one of a fixed value (I can't remember what value). I noticed that as my hand moved close to the circuit a tone was generated in the ear piece that changed in a non-linear fashion. There would be a tone, then silence, a different tone, then more silence as my hand moved closer or further from the circuit. It also worked with electrical wiring behind a wall, whether or not the wire was part of an active circuit. So, are the lines of force you see in diagrams of magnetic fields actual, measurable, lines of force with 'gaps' of lesser strength between them? What about gravitational fields and electromagnetic fields? I've tried researching it on the net, but I'm definitely not up with the technical aspects!