Forumerker: I type in follow-up to JimIvey's and MYK's posts. Jim's tongue-in-cheek statement re: Chisum makes the point. To wit, it can be darn complicated. MYK's post introduces the "duh factor", highlighting the difference betwen legal obviousness and what an artisan, for example an experienced bench chemist, would think to be "obvious".
Long before I was a patent attorney, I was one of those bench chemists. After just getting my PhD and starting work in industry, I'd read a recently issued patent and think, "what's heck is the big deal? Duh, anybody could have thought of that!" Well, anybody didn't but patentee did. The law of obviousness, as applied today and (re)confirmed by SCOTUS in KSR (also mentioned by JimIvey), is set-out in Graham v. John Deere. There are many factors to consider, including level of skill in the art, which is not "Nobel" level.
Before attacking 500+ pages of Chisum, indeed a good secondary source, you might try the "condensed version" in Patent Law Basics (Mills, ca 100 pgs)), or the even more compact Patent Law Fundamental (Schwarz)