MR. PRESIDENT,--The Senator from Illinois [Mr. TRUMBULL], in former days, was a sincere, intelligent, devoted supporter of the Wilmot Proviso. As I understand that Proviso, it was simply a prohibition of Slavery in the Territories. Now I know not whether the Senator held, as I did, that, even without that prohibition, yet, by a strict interpretation of the Constitution, Slavery could not go into the Territories. I presume he did; most of us did. For myself, I held it resolutely and sincerely. I always regarded the Wilmot Proviso, if the Constitution were properly interpreted, as mere surplusage, sheer supererogation; and yet I never hesitated, in season or out of season, to vindicate it; and I believe the Senator never hesitated, in season or out of season, to do the same. I remember that my earliest admiration of that Senator was founded on his brave and able support of that very prohibition. Not then was he deterred from a humane provision because without it, according to his interpretation of the Constitution, Slavery could not enter the Territories. Nor was he deterred because the provision might be offensive to persons of weak nerves. No, Sir; openly and courageously he maintained the principle that Slavery must be prohibited. And on the same principle--if I may pass from great things to smaller, I admit, but not small--I insist that this proviso should also be adopted. Our experience shows that the law as the Senator expounds it is not so accepted by this railroad corporation. He knows as well as I that colored persons are daily insulted. Some of these victims will compare in respectability of conduct with any whom I now have the honor to address. My colleague alluded to a colored clergyman whom he saw thrust out only the other day. We know of an officer of the United States, wearing the national uniform, thrust out; and the Senator from Illinois will allow all these things to be done, and not interfere. He tells us that it is contrary to law, and yet he allows it to proceed under the very eyes of the Senate. Sir, I insist that the Senate, when such outrage occurs, shall show that it has power, and is willing to exercise it on the side of justice.