Ex-Mayor Harper, whom we have found to be one of the most affable and estimable gentlemen in the city of New-York, informed us, sometime ago, that, though he had no means of knowing positively, he was of the opinion that about eighty per cent. of all their publications find final purchasers in the free States--the remainder, about twenty per cent., in the slave States. Yet it is probable that, with one or two exceptions, no other publishing house in the country has so large a per centage of Southern trade. Of the "more than three hundred houses engaged in the publication of books," to which the writer in the "American Publishers' Circular" refers, upwards of nine-tenths of the number are in the non-slaveholding States, and these represent not less than ninety-nine hundredths of the whole capital invested in the business. Baltimore has twice as many publishers as any other Southern city; and nearly as many as the whole South beside. The census returns of 1850 give but twenty-four publishers for the entire South, and ten of these were in Maryland. The relative disproportion which then existed in this branch of enterprise, between the North and the South, still exists; or, if it has been changed at all, that change is in favor of the North. So of all the capital, enterprise and industry involved in the manufacture of the _material_ that enters into the composition of books. All the paper manufactories of the South do not produce enough to supply a single publishing house in the city of New-York.--Perhaps "a Southern Literature" does not necessarily involve the enterprises requisite to the _manufacture_ of books; but experience has shown that there is a somewhat intimate relation between the author, printer, paper-maker and publisher; in other words, that the intellectual activity which expresses itself in books, is measurable by the mechanical activities engaged in their manufacture.--Thus a State that is fruitful in authors will almost necessarily be fruitful in publishers; and the number of both classes will be proportioned to the _reading_ population. The poverty of Southern literature is legitimately shown, therefore, in the paucity of Southern publishers. We do not deny a high degree of cultivated talent to the South; we are familiar with the names of her sons whose genius has made them eminent; all that we insist upon is, that the same accursed influence which has smitten her industrial enterprises with paralysis, and retarded indefinitely her material advancement, has exerted a corresponding influence upon her literature. How it has done this we shall more fully indicate before we close the chapter.