In the fifteenth article of the treaty of commerce and navigation the British government had reserved the right of countervailing these discriminating duties, and the United States had bound themselves not to impose any new or additional duty on the tonnage of British ships or vessels, or to increase the then subsisting difference between the duties payable on the importation of any article in British American ships; so that when Congress imposed increased duties, the English Parliament exercised the reserved right stipulated in the treaty, and thus by the Act of Geo. III., c. 97, countervailing duties were imposed, payable on the importation of American goods in American vessels, in addition to the duties payable on their importation in British ships.[317] Additional duties were also imposed upon certain specified articles, and three per cent. _ad valorem_ upon enumerated articles. [Sidenote: Effect of legislative measures on both sides.] Such, then, was the legislation on both sides, as it most materially affected merchant shipping. The American shipowners and merchants looked upon every proceeding on the part of the British Legislature as levelled especially against themselves; and, jealous of everything which militated against their own interest, they contended that the Parliament of Great Britain had exceeded the fair intent and meaning of the treaty of 1794, and had secured for the British shipowners the exclusive carriage to Great Britain, in time of peace, of some of the most important objects of American exportation. They pointed out that the English had selected fish, oil, and tobacco, articles of great bulk, as objects on which the highest countervailing duties had been imposed. They alleged that in consequence of this countervailing duty upon oil, a British ship of two hundred and fifty tons register, carrying two hundred and fifty tuns of oil to great Britain from the United States, would pay 453_l._ 15_s._ sterling less duty thereon than the same oil would pay if imported into Great Britain in an American ship. By a similar operation, a British ship of two hundred and fifty tons, carrying four hundred hogsheads of tobacco, of one thousand two hundred pounds each, to Great Britain from the United States, would pay 360_l._ sterling less duty than would be payable on the same quantity of tobacco imported in an American ship; the whole freight, at 35_s._ sterling per hogshead, would only amount to 700_l._ sterling, which, after deducting the countervailing duty of 360_l._, would leave to the American a net freight of only 344_l._ 1_s._ sterling.