Through the centuries, lawmakers have resorted to a variety of measures to combat air pollution. During the middle ages, for example, King Edward I of England established a reputation as an uncompromising environmentalist by executing a man for burning coal instead of oak. Although they may share Edward’s sense of urgency, most modern-day advocates of a cleaner environment favor less harsh measures. Indeed, economists have long argued that Adam Smith’s invisible hand can be more effective than the regulatory axe in cotrolling pollution