The Civil War tariffs continued with minor revisions until the general revision of 1883. This act increased the duties on some products and reduced them on others. The general average of the rates, however, was not greatly changed. Under the Act of 1890 the protective system was greatly extended and duties were increased in that act as well as many products removed from the free list. Com pound or mixed duties were freely used in this act and the duties on many products were higher than ever before.
The high protective duties in the McKinley Act of 1890 were strongly contested in the political campaign of 1892 and after a change of ad ministration with the election of Cleveland, Congress set about revising the tariff downward. Substantial changes were made in the Act of 1894 but it was far from a free trade bill.
In 1896 the administration changed again and a highly protective act was passed in 1897. This continued in effect for an unusually long period, namely, until 1909 when duties were increased on the average still further.
With the change of administration in 1913, a new and lower tariff act was passed which continued in effect until 1922, at which time duties were again increased all along the line in the tariff act of that year. The Act of 193o still further increased the duties on most duti able products.
there are given the average ad valorem rates o duties on dutiable and upon total imports for the year immediate': following the enactment of important tariff acts since 186o. It is important to recall that these ad valorem comparisons among variou acts may be deceptive from the point of view of the amount of pro tection offered American industry. In the first place, changes in price of products may greatly affect the ad valorem calculations and in second place some of the higher duties may so reduce the imports o the products to which they apply that they have small weight in calculat ing the averages. Furthermore, the protective principle may be gradual': extended to a wider and wider range of articles for which the new dutie may be low or moderate, thereby reducing average rates. These fact probably account for the impression obtained from the table that thy ad valorem rates of duty on dutiable imports have been gradually de clining since the Civil War, whereas, as a matter of fact, the protective principle had been gradually spreading since that time with minor recessions in 1894 and 1913, until 1934 when a definite change of far, reaching movement took place.
The underlying principle of reciprocity is to offer positive and definite inducements to individual foreign nations to co-operate in a program of mutual reduction of trade barriers in the form of lower United States tariffs on items which others wish to sell in exchange for concessions from other nations on items which the United States seeks to sell. A reduction of tariff barriers gen erally is sought by recourse to the most-favoured-nation formula bilaterally applied.