672 International Organization 60 55 05 40 3 52015 10 1820 1840 1860 18801900 1920 1940 1960 1980 Year -Customs revenue as a percentage of imports --Regular customs revenue as a percentage of dutiable imports FIGURE 1.Levels of protection in the United States,1824-1994 instance,if imports of low-duty goods increase for some reason.8 The measures also cannot discriminate between duties levied for revenue rather than protective reasons: any significant shift away from the reliance on the tariff for revenue generation is likely to overstate reductions in tariff protection.Such a shift,of course,occurred in the United States in the late 1920s and 1930s with the increasing dependence on personal and corporate income taxes.? In addition,nontariff forms of protection,which do not generate customs revenue, have become increasingly important in the wake of the post-1934 tariff reductions.10 In fact,new import quotas on a range of agricultural goods played a major role in trade agreements after 1934.The Jones-Costigan Act,passed in the same year,pro- vided for quotas on imports of sugar,wheat,rye,barley,dairy products,cotton,oats, and a range of other farm goods.In 1937 quotas were introduced on dairy products, beef,potatoes,and lumber that effectively offset negotiated tariff reductions on Cana- dian imports.New quotas on tobacco,cotton,and crude oil were adopted in follow- 8.Irwin 1993. 9.Studenski and Krooss 1963,406. 10.See Bhagwati 1988;and Baldwin 1993 11.Goldstein 1993,156.672 International Organization 1820 1840 1860 1880 1900 1920 1940 1960 1980 Year -Customs revenue as a percentage of imports - - Regular customs revenue as a percentage of dutiable imports FIGURE 1. Levels ofprotection in the United States, 1824-1994 instance, if imports of low-duty goods increase for some rea~on.~ The measures also cannot discriminate between duties levied for revenue rather than protective reasons: any significant shift away from the reliance on the tariff for revenue generation is likely to overstate reductions in tariff protection. Such a shift, of course, occurred in the United States in the late 1920s and 1930s with the increasing dependence on personal and corporate income taxes9 In addition, nontariff forms of protection, which do not generate customs revenue, have become increasingly important in the wake of the post-1934 tariff reduction^.'^ In fact, new import quotas on a range of agricultural goods played a major role in trade agreements after 1934. The Jones-Costigan Act, passed in the same year, pro￾vided for quotas on imports of sugar, wheat, rye, barley, dairy products, cotton, oats, and a range of other farm goods." In 1937 quotas were introduced on dairy products, beef, potatoes, and lumber that effectively offset negotiated tariff reductions on Cana￾dian imports. New quotas on tobacco, cotton, and crude oil were adopted in follow- 8. Irwin 1993. 9. Studenski and Krooss 1963,406. 10. See Bhagwati 1988; and Baldwin 1993. 11. Goldstein 1993, 156