Sunday, 21st.—The rebel army, reported at eighty thousand, but probably a small portion of it, numbering less than one quarter of that estimate, was encamped last night, within two miles of where we halted this morning. They left, however, on our approach, and we did not get sight of them. We moved again at 9 o’clock this morning, and having wandered through the fields for two hours, apparently without a definite object, we have again bivouaced almost in sight of Williamsport. We are in a beautiful grove, and here I hope we shall be permitted to spend the Sabbath in quiet. The enemy has escaped our “bag,” and why splutter on now, as if we meant to do something. I am now satisfied that this army will win no decisive battle whilst under command of General George B. McGlellan. It is not apart of his programme.