If you like something a bit more exhaustive (well, a lot more, to be honest. You need at least a working knowledge of phonological features), I'd recommend H.H. Hock's "Principles of historical linguistics". It's dry material, unless you're a total geek like me

Also: I found a torrent with a ton of books on linguistics a while back, some of which are relevant to your question. They're on my old laptop however, and can't look it up for you at the moment (can't seen to find the torrent on the internet, for some reason). But I'll take a look if you're interested.