Without any doubt, Maxwell's theory of electromagnetism is the foundation of modern physics and relativity. I am always impressed by how it is easy to learn, and conversly I am disappointed by my ignorance about how Maxwell did his job. Would some of you know about a good reference describing how Maxwell designed his equations. What was known at the beginning, in which form, what were the problems to be solved, how they were solved and why they were solved the way Maxwell did. It is always impressing for me to thing that electrostatics and magnetism led to a theory of light and to relativity. For me there is a kind of mystery there that can only be understood by going back in time.