Apple made its new Apple Music logo by playing a song into a tray of oil and filming the ripples. No CGI. Fred again.. wrote the music, a speaker shook the oil, and a camera caught what happened. The catch is that a tray of oil only cooperates with certain notes, and the reason why goes back to a math prize Napoleon put up over 200 years ago. Here's how the trick works. Every ripple on a liquid acts like a little lens. The logo sits behind the oil, so as the surface curves, the light coming…