It's a contraption that makes the lists of "Greatest Inventions Ever"; at the same time, it's accused of causing global disaster. It has changed everything from architecture to people's food habits to their voting patterns, to even the way big business washes its windows. It has saved countless lives . . . while causing countless deaths. Most of us are glad it's there. But we don't know how, or when, it got there. It's air conditioning. For...