On this subject of what is called abroad the prejudice of color, the North has been censured, even by many of our best friends. But it is impossible for Europe, where the African race are not, and never have been, either as slaves or freemen, to solve for us this most difficult problem of the social equality of the white and black races. Where marriage between them is unknown, such social equality cannot exist. Europe has an idea and a theory, but no practical knowledge of the subject. We have the facts and experience. Efforts have been made here for a century to establish this social equality, but the failure is complete. New England has devoted years of toil and thousands of dollars to accomplish this object, and the Quakers, and Franklin's Pennsylvania society, spared neither time nor money. Statesmen, philanthropists, and Christians have labored for years in the cause, but the case grows worse with each succeeding census. State after State, including now a large majority, forbid their introduction. The repugnance is invincible, and the census of 1840 (as shown by the tables annexed to my Texas letter of January, 1844) proved that one sixth of the negroes of the North are supported by taxation of the whites--a sum which would soon colonize them all. The free negroes, regarded here as an inferior caste, have no adequate motive for industry or exertion. Each year, as their numbers augment, intensifies the prejudice, invites collision in various pursuits, with competition for wages, and renders colonization more necessary. We must not any longer keep the free negro here in an exhausted receiver, or mix the races, as chemical ingredients in a laboratory, for the edification of experimental philosophers. Such empiricism as regards the negro race, after our repeated failures, is cruel and unjust. We have made the trial here for nearly a century, and the race continues to retrograde. Compare their progress and condition in America and Liberia, and what friend of the race or of humanity can desire to retain them among us? The voice of nature and of experience proclaims, that America is our home and Africa is theirs; and let us, in a spirit of true kindness and sympathy for them, obey the mandate. There will soon be a great change among the free blacks on this subject. When Liberia shall expand and become a considerable power--when she shall have great marts of commerce, and her flag shall float in our harbors--when the Messages of her President, the reports of her Cabinet, the debates in her Congress shall be read here, her ministers and consuls be found among us, and the ambition of her race shall thus be aroused, we shall probably have as great a negro exodus from our country to Africa, as there ever was from Europe to America.