Sir,--The Secretary of War has laid before the President several despatches which were received yesterday and to-day from Major-Gen. Meade, who is commanding the United States forces on the Canadian frontier. These communications warrant the President in believing that the so-called Fenian expedition is now entirely, at an end, and that order and tranquility may be expected to prevail henceforth on that border. I regret, however, that I am obliged to connect with this gratifying information the further statement that reports have reached Major-Gen. Meade to the effect that some of the Canadian or British troops have crossed the line and entered within the territory and jurisdiction of the United States. It is even said that this entry took place after the disturbers of the peace under the command of the leader Spear had relinquished their forbidden enterprise and withdrawn within the boundary line of the United States. The reports go so far as to say that prisoners have been taken on the soil of the United States and conveyed to Canada, and that the Canadian agents have threatened that these prisoners, together with such stragglers as may now lie found within the Canadian lines, will be executed without legal trial. It is believed that these reports are exaggerated. Care has been taken by Major-Gen. Meade to have them promptly investigated. In the meantime I am instructed by the President to represent to you, and through you to the British and Canadian authorities, that this Government would not look without serious concern upon the practice of any retaliation or other illegal proceedings upon the persons of such of the offenders as have fallen, or shall hereafter fall, into the hands of the Canadian authorities. I respectfully invite your attention to the subject, with the confident expectation that no proceedings that are not authorized and in conformity with law, will be taken against persons of that class, and in the hope that even the customary administration of the law will be tempered with special forbearance and clemency. In view of the effective proceedings which this Government has adopted in regard to the disturbances now so fortunately ended, these representations would have been made by me without waiting to be moved from any other quarter. They are now made, however, with the approval of Major-Gen. Meade, and I believe that they will receive the concurrence of the Congress and people of the United States. I have the honor to be, sir, Your obedient servant, WILLIAM H. SEWARD. The Hon. Frederick W. A. Bruce. TRIALS OF THE FENIAN PRISONERS.