HEADQUARTERS OF THE ARMY OF THE POTOMAC Washington, September 8.

Private William Scott, of Company K. of the Third regiment of Vermont volunteers, having been found guilty by court martial of sleeping on his post while a sentinel on picket guard, has been sentenced to be shot, and the sentence has been approved and ordered to be executed. The commanding officers of the brigade, the regiment and the company, of the command, together with many other privates and officers of his regiment, have earnestly appealed to the Major-General commanding, to spare the life of the offender, and the President of the United States has expressed a wish that as this is the first condemnation to death in this army for this crime, mercy may be extended to the criminal. This fact, viewed in connection with the inexperience of the condemned as a soldier, his previous good conduct and general good character, and the urgent entreaties made in his behalf, have determined the Major-General commanding to grant the pardon so earnestly prayed for. This act of clemency must not be understood as affording a precedent for any future case. The duty of a sentinel is of such a nature, that its neglect by sleeping upon or deserting his post may endanger the safety of a command, or even of the whole army, and all nations affix to the offence the penalty of death. Private William Scott of Co. K. of the Third regiment of Vermont volunteers, will be released from confinement and returned to duty.

By command of Maj.-General McClellan, S. WILLIAMS, Asst. Adjt.-General.