Such have been the effects of free-trade principles on the comparative prosperity of British and foreign shipping, on the showing of the Free-traders themselves, and according to the figures which their great statistician, Mr Porter, has prepared and published at the Board of Trade. We were unwilling to mix up a great national question, such as the repeal of the Navigation Laws, with any subordinate examination as to the accuracy or inaccuracy of the view of our maritime affairs which these figures exhibit. Such is the strength of the case, that it will admit of almost any concession; and the opponents of their repeal have no occasion to go farther than to the statistics of their adversaries for the most decisive refutation of their principles. But there are two observations on the tables published by the Board of Trade, so important that they cannot be passed over in silence. The first is, that in 1834, when Mr Poulett Thomson was president of the Board of Trade, a regulation was made by the Board as to the measurement of vessels, which had the effect of adding _a fifth_ to the apparent tonnage of all British vessels, subsequent to that date. This change was clearly proved by the witnesses examined before the Commons' committee; but though Mr Porter, in his last edition of the _Progress of the Nation_, mentions the change, (p. 368,) he makes no allusion to it in comparing the amount of British and foreign tonnage since 1834. Of course a fifth must be deducted from British tonnage, as compared with foreign, since that time; and what overwhelming force does this give to the facts, already strong, in regard to the effect of the reciprocity system on our maritime interests!