Of these Essays, which were written in 1829 and 1830, the fifth alone has been previously printed. The other four have hitherto remained in manuscript, because, during the temporary suspension of public interest in the species of discussion to which they belong, there was no inducement to their publication. But in regard to those duties on foreign commodities which do not operate as protection, but are maintained solely for revenue, and which do not touch either the necessaries of life or the materials and instruments of production, it is his opinion that any relaxation of such duties, beyond what may be required by the interest of the revenue itself, should in general be made contingent upon the adoption of some corresponding degree of freedom of trade with this country, by the nation from which the commodities are imported.