The preceding letter of Mr. Barker, furnishes grounds for the belief, that _hundreds_, if not _thousands_ of free colored persons, from the different states of this Union, both slave and free from the West Indies, South America, Mexico, and the British possessions in North America, and from other parts of the world, are reduced to slavery _every year_ in our slave states. If a single individual, in the course of a few days, _accidentally_ discovered _six_ colored free men, working in irons, and soon to be sold as slaves, in a _single_ southern city, is it not fair to infer, that in all the slave states, there must be _multitudes_ of such persons, now in slavery, and that this number is rapidly increasing, by ceaseless accessions? The letter of Mr. Barker is valuable, also, as a graphic delineation of the 'public opinion' of the south. The great difficulty with which the release of these free men was procured, notwithstanding the personal efforts of Mr. Jacob Barker, who is a gentleman of influence, and has, we believe, been an alderman of New Orleans, reveals a 'public opinion,' insensible as adamant to the liberty of colored men. It would be easy to fill scores of pages with details similar to the preceding. We have furnished enough, however, to show, that, in all probability, _each_ United States' census of the _slave_ population, is increased by the addition to it of _thousands_ of free colored persons, kidnapped and sold as slaves. 5th. To argue that the rapid multiplication of any class in the community, is proof that such a class is well-clothed, well-housed, abundantly fed, and very _comfortable_, is as absurd as to argue that those who have _few children_, must of course, be ill-clothed, ill-housed, badly lodged, overworked, ill-fed, &c. &c. True, privations and inflictions may be carried to such an extent as to occasion a fearful diminishment of population. That was the case generally with the slave population in the West Indies, and, as has been shown, is true of certain portions of the southern states. But the fact that such an effect is _not_ produced, does not prove that the slaves do not experience great privations and severe inflictions. They may suffer much hardship, and great cruelties, without experiencing so great a derangement of the vital functions as to prevent child-bearing. The Israelites multiplied with astonishing rapidity, under the task-masters and burdens of Egypt. Does this falsify the declarations of Scripture, that 'they sighed by reason of their bondage,' and that the Egyptians 'made them serve _with rigor_,' and made 'their lives bitter with _hard bondage_.' 'I have seen,' said God, 'their _afflictions_. I have beard their _groanings_,' &c. The history of the human race shows, that great _privations and much suffering_ may be experienced, without materially checking the rapid increase of population.