I am attempting to understand a question posed to me by an acquaintance, who asked me if I could refer him to literature freely available on the Internet on "self-dual solutions to Maxwell's equations on Euclidean space, or pseudo-Euclidean space, not Minkowski space (where there are none)" and he labeled them "instantons". I'm lost, so my questions: (a) aren't instantons solutions to equations of motion? Can you consider Maxwell's equations as equations of motion? (b) In what sense are solutions to such equations self-dual, or more simply, what concept of duality is meant here? (c) does anyone have any appropriate literature (freely available on the Internet) to recommend to answer my acquaintance's question? Any indications on any or all of these questions would be greatly appreciated.