...bstance as follows: A dispatch just received from Colonel Don Piatt says, I read Halleck's last despatch by the light of his of the thirtieth April, and considered it a positive order to fall back to Harper's Ferry , and I so ordered Milroy. I have been on the ground and gave it advisedly. Milroy cannot move from his present position in presence of the enemy. He has not transportation enough to move in fac...