Hey folks, I've been looking for a good biography of Einstein, but I'm especially interested in the story of his development of relativity (both of them!) from a technical standpoint. Most of the Einstein bios at, say, the local Barnes and Noble are geared towards a general audience and have scarcely a plus sign, much less a tensor or two! Meanwhile, textbooks explain the theories after we've had a century or so to work them out more cleanly. Can anyone recommend a good book that focuses on the history of relativity as well as the science?