Alright, at least I know I'm not missing something obvious. As for coiling the wire, can I coil it multiple times? As in, coil from left to right across the nail, then start back again from the left side? Or does that not increase the field at all?
I'm trying to generate a magnetic field that's strong enough to be detectable (i.e., still stronger from the Earth's field) at some distance away from where I'm generating it. I have a pretty simple setup with some current running through a wire wrapped around a nail, and I can detect it up to...