Familiar as these truths are to all they seem to have been, in an unaccountable manner, forgotten by our modern political economists; and the oblivion of them is the principal cause of the remarkable failure which has attended the application to practice of all their theories. They invariably forget the different age of nations; they overlook the essential difference between communities with different national character, or in different stages of manufacturing or commercial advancement, and fall into the fatal error of supposing that one general system is to be readily embraced by, and found applicable to, a cluster of nations existing under every possible variety of physical, social, and political circumstances. Fixing their eyes upon their own country, or rather upon the peculiar interest to which they belong in their own country, they reason as if all mankind were placed in the same circumstances, and would be benefited by the arrangements which they find advantageous. They forget that all nations were not planted at the same time, nor in the same soil; that the difference in their age, the inequality in their growth, the variety in their texture, is as great as in the trees of the forest, the seeds of which have been scattered by the hand of nature; that the incessant warfare of the weaker with the stronger, exists not less in the social than the physical world; and that all systems founded on the oblivion of that continued contest, must ever be traversed by the strongest of all moral laws--the instinct of SELF-PRESERVATION. We have said that the modern theories when applied to practice, have, in a remarkable manner, failed. In saying so, we have chiefly in view the acknowledged failure of the strenuous efforts made by England, during the last twenty years, to effect an interchange in the advantages of free trade, and the entire disappointment which has attended the long establishment, on a great scale, of the reciprocity system. To the first we shall advert in the present paper; the second will furnish ample room for reflection in another.