Such is the issue, simply stated. On the one side are women and children at the auction-block, families rudely separated, human flesh lacerated and seamed by the bloody scourge, labor extorted without wages; and all this frightful, many-sided wrong is the declared foundation of a mock Commonwealth. On the other side is the Union of our fathers, with the image of Liberty on its coin and the sentiment of Liberty in its Constitution, now arrayed under a patriotic Government, which insists that no such mock Commonwealth, having such declared foundation, shall be permitted on the national territory, purchased with money and blood, to impair the unity of our jurisdiction, and to insult the moral sense of mankind. Therefore the battle waged by the Union is for Civilization itself, and it must have aid and God-speed from all not openly for Barbarism. Every one must give his best efforts, and especially the young men to whom I now appeal. CHARLES SUMNER. WASHINGTON, 4th July, 1863. LET COLORED MEN ENLIST. LETTER TO A CONVENTION AT POUGHKEEPSIE, NEW YORK, JULY 13, 1863. BOSTON, July 13, 1863. DEAR SIR,--It will not be in my power to take part in the proposed meeting at Poughkeepsie. But I am glad it has been called, and I trust it will be successful. To me it has been clear from the beginning that the colored men would be needed in this war. I never for a moment doubted that they would render good service. And thus far the evidence in their favor is triumphant. Nobody now questions their bravery or capacity for discipline. All that can be said against them is that they are not “white.” But they have a special interest in the suppression of the Rebellion. The enemies of the Union are the enemies of their race. Therefore, in defending the Union, they defend themselves even more than other citizens; and in saving the Union, they save themselves. I doubt if in times past our country could have justly expected from colored men any patriotic service. Such service is the return for protection. But now that protection has begun, the service should begin also. Nor should relative rights and duties be weighed with nicety. It is enough that our country, aroused at last to a sense of justice, seeks to enroll colored men among its defenders. If my counsels could reach such persons, I would say, Enlist at once. Now is the day, and now the fortunate hour. Help to overcome your cruel enemies battling against your country, and in this way you will surely overcome those other enemies, hardly less cruel, here at home, who still seek to degrade you. This is not the time to hesitate or to higgle. Do your duty to our common country, and you will set an example of generous self-sacrifice which must conquer prejudice and open all hearts.